Month: August 2020

Wasps, Surprisingly Cool Pollinators

Cerruti R2 Hooks$ and Anahí Espíndola*
$Associate Professor and Extension Specialist, CMNS, Department of Entomology
*Assistant Professor, CMNS, Department of Entomology. Twitter: @Analyssi

Note: This is the seventh and final article of our series on pollinators. Initial articles can be found in the vegetable and fruit headline news June, July and August special editions and Maryland Agronomy News Blog.

Introduction

Among insects, wasps (Hymenoptera) which consist of social, parasitic and solitary species exhibit great variations in structure, physiology and behavior (Fig. 1). Further, due to their important roles in ecosystem functioning as pollinators, predators and parasitoids, wasps are studied extensively in agricultural systems and are of specific interest for conservation. There are at least 850 species of social wasps and the vast majority of wasps are solitary (>75,000 species), or parasitic (>650,000 species). Though bees are often mistaken for wasps, a simple way to differentiate them is that wasps contain a pointed lower abdomen and a narrow petiole “waist” that separates the abdomen from the thorax. Also, wasps tend to be less hairy than bees (Figs. 1, 2) and thus are less fuzzy. The lack of hairs does not allow for many pollen grains to attach to their bodies. Consequently, wasps are much less efficient at carrying pollen than their bee relatives. Further, being carnivorous, wasps are interested in flower blossoms mostly as a nectar source, and not as a source of proteins (from pollen). Nevertheless, some wasp species are able pollen vectors, and many play a crucial role as specialist pollinators. Some may be classified as excellent pollinators and in certain systems are much more efficient at pollination than their fuzzy-haired bee cousins. Wasps in one family (Masaridae) have gone through the same dietary transition that bees went through when they evolved to a completely plant-based from a carnivorous diet. Today, this family display dietary similarities with bees, in that they collect and provision larval cells with pollen and nectar, instead of with animal material. In this article, we will demonstrate that wasps do not deserve their “bad guy” image, and that they are more than nuisances or biological control agents. We will show that wasps are fascinating creatures and central to the reproduction of many wild and crop plants.

wasp on a mint flower
Fig. 1. Male European Beewolf (Philanthus triangulum) solitary wasp on mint. Photo: M. Cooper (CC)
wasp on a white flower
Fig. 2. Hairy wasp possibly Vespa sp. on flower. Photo: R. Fontana (CC)

Food requirements

As stated earlier, the vast majority of wasps are carnivorous. However, these wasps cannot survive based on a completely meat-diet; they in fact need to supplement their diets with sugar and water, which very often comes from flower nectar, or honeydew produced by insect herbivores (e.g., aphids). Similar to bees, wasps have high energy requirements, and pollen and nectar allow them to acquire extra energy to use for their high metabolisms. For this same reason, it is not uncommon to observe wasps feeding on fruits (e.g., apples, pears, grapes and blackberries; Fig. 3), fruit juices, honey, jam and pies.

wasp on fruit
Fig. 3. Paper wasp (Polistes sp.) feeding on blackberry. Photo: A. Leslie (UMD Extension).

Some wasps, such as yellow jackets, have diverse diets and can consume some of the same foods that humans eat, which is why we often find them swarming our picnic plates and garbage cans. Carnivorous wasps are hunters, and prey on other insects and arthropods, including herbivores that feed on important crops. True wasps have stingers and use them to capture insects or spiders as food for their larvae. Other wasps are parasitic and use their ovipositors to lay eggs on or in the bodies or eggs of other insects, which then become their hosts. In those cases, the immature wasp or developing larva develops inside the host while feeding on its tissues. Many species of parasitic wasps use hosts as direct food or for oviposition. Some female parasitoids feed from and oviposit eggs on the same host individual, while females of other species may use a host solely for food or oviposition. When host feeding occurs, females are believed to obtain nutrients that can be used to produce more eggs, and to enable further host searches.

Importance as pollinators

Wasps are an important part of the flower-visiting guild and often frequent flowers in search of nectar and/or insect prey. Some wasps are considered generalist pollinators, and passively transfer pollen while feeding on nectar from various plants. While doing so, they often overlap with other pollinators, such as bees, flies or butterflies. However, because they generally lack abundant body hairs and do not feed on pollen, they are considered less efficient pollinators than their bee relatives. Further, some behave more frequently as nectar thieves than as true pollinators, especially when they pierce the base of flowers to access the nectar without contacting the plant’s reproductive organs. This said, despite not having the reputation of bees, wasps can and do effectively contribute to pollination. In some plant systems and environments, they can become the most efficient pollinator, surpassing bees. For example, in a study involving pollinators and the plant Schinus terebinthifolius (Fig. 4a), some social wasp pollinators were more abundant and species-rich than bee visitors. Another study found that in some environments, the western yellowjacket (Vespula pensylvanica, Fig. 4b) was a more effective pollinator than the honey bee (Apis mellifera). In that investigation, it was observed that pollen of the plant Scrophularia californica was more efficiently transferred by Vespula wasps and Bombus bees (bumblebees) than by honey bees, which visited the plant but did not pollinate. In this same study, the median number of pollen grains delivered per individual floral visitor also varied among the groups (Apis = 4, Bombus = 9, and Vespula = 34). As a result, this study demonstrated that even though honey bees seemed to be the most abundant floral visitor, the western yellowjacket was the most effective pollinator. Though wasps are sometimes the best pollinator of some generalist flowers, they are typically recognized as specialist pollinators. Specialist unlike generalist pollinators, are very selective in their floral choices, and frequent flowers of one or a very few plant species. In instances where this type of specialization has evolved, rewards involved are either special (e.g., brood site) or inexistent in that the wasp is lured and exploited by the plant. In either case, the plant reproduction relies exclusively on these specialized visitors.

Figs. 4. Top) Schinus terebinthifolius flowers and Bottom) Western Yellowjacket (Vespula pensylvanica) drinking water. Photos: D. Valke and K. Schulz (CC).

Wasp flowers

Generalist flowers that attract wasps have specific floral traits, such as dull coloration, unusual odor, and readily accessible (exposed) and concentrated nectar. Most wasp can see UV light, and tend to visit white- or yellow-colored flowers such as those in the parsley (Apiacea) family. The majority of wasps have very short mouthparts or tongues, and as such, can obtain nectar only from shallow flowers. Wasp-pollinated flowers can produce either large or small amounts of nectar. One of the plants that are usually visited by wasps is in the orchid family. This plant is pollinated in part or exclusively by social wasps, and is known to secrete abundant nectar, accessible in shallow floral depressions or short spurs. These “wasp” orchid plants also display dull-colors and strongly scented flowers, and are usually avoided by other flower-frequenting insects.

The complexity of floral morphology is usually directly related to their level of pollination specialization. In fact, this complex morphology allows plants to limit nectar availability to one or a few pollinator species that have the “right” matching morphology that allows them to reach the nectar reward. Other traits that plants can evolve are specific odors, which are only perceived by and subsequently attract specialized group of pollinators. It is believed that floral scents play a key role as a selective attractant in numerous specialized pollination systems involving plants and wasps. This is the case of two African pineapple lilies of genus Eucomis. A study showed that two of these plant species – E. autumnalis and E. comosa – are involved in a specialized pollination system with spider wasps (family Pompilidae) in the genus Hemipepsis. Even though flowers of these plants display cryptic coloration (pale yellow-green), the flowers produce strong scents that are only exceptionally attractive to the main pollinators (i.e., spider wasps). Similarly, while the African milkweed Pachycarpus grandifloras (Fig. 5a) has open flowers with abundant and concentrated nectar, they are visited and pollinated almost exclusively by Hemipepsis spider‐hunting wasps (Fig. 5b). In this plant species, it was determined that the achieved specialization with Hemipepsis wasps was facilitated by the production of unpalatable nectar, cryptic coloring and scent, all of which are strong attractants to the pollinating wasps. Though very effective in specialized systems, floral scents are successfully used to attract social wasps in the genus Vespula to the pale yellow-green orchid Coelogyne fimbriata.

Figs. 5. Top) Pachycarpus grandiflorus flowers and Bottom) South Africa spider‐hunting wasps (Hemipepsis sp). Photos: P. Warren and R. Fourie (CC).


Special relationship with orchid – Wasps are well known for their specialized pollination relationship with orchids, with at least 100 species of orchids solely dependent on wasps for pollination. Among these, pollination by sexual deception may be among the most fascinating specialized pollination systems that exist. In many instances, the attractant for pollinators is the orchid’s mimicry of members of the opposite sex. Relative to this, many orchid species display morphologies that mimic the female wasp, thus attracting and tricking male wasps. How they do this? In most cases, it has been shown that these orchids mimic the general appearance and chemical scent of female wasps of specific wasp species. When a male wasp attempts to mate with the “female” (the orchid labellum), it receives and then transfers pollen it collected in a previous floral visit. Sexually-deceptive orchids exist in many parts of the world, with the Mediterranean and Australia recognized as epicenters of sexually-deceptive pollination systems. In Australia, the vast majority of sexually-deceptive orchids are pollinated by thynnine wasps, which patrol areas in search of wingless female wasps to mate with (Fig. 6). In Europe, the most impressive case of sexual-deception is that of species in the orchid genus Ophrys, which have evolved specific odor cocktails to attract different sphecid wasps. Other orchids have been shown to use non-sexual mimicry to attract wasps. A recent study found that two European orchids (Epipactis helleborine and E. purpurata) have developed a chemical-mimicry system in which their flowers release green-leaf volatiles to attract vespid pollinators (Vespula germanica and V. vulgaris). Green-leaf volatiles are typically produced by plants when they are being fed on by herbivores such as caterpillars, and are used by vespid wasps as a cue to find caterpillar prey. Orchids have exploited this cue and evolved the ability to produce these volatiles to specifically lure vespid pollinators into visiting and pollinating their flowers. Thus, orchids are sneaky and have evolved complex ways to attract pollinators, using a mixture of physiological, morphological and chemical deception.

Fig. 6. Thynnine wasp in an orchid. Photo: M. Whitehead (CC).

Pompilid wasps

Though this article is meant to serve as a general synopsis of wasp pollination, it is unmanageable to talk about pompilid wasps and pollination (briefly conferred earlier) without commenting at least momentarily on these wasp’s spider hunting behavior (Fig. 5b). Certainly, adult spider wasps are commonly found on flowers. Howbeit, they are also frequently situated on the ground or hovering above in search of prey, specifically spiders. Thus, spider wasps are known more for their spider hunting than their pollination skills. Spider wasps capture spiders by paralyzing them with a sting. They sometimes kill the spider almost instantly and in other occurrences, the spider may survive for a few weeks. Once the spider is paralyzed, a female pompilid makes a wasp’s nest (burrow) or flies or drags the spider to a previously made burrow. A single wasp egg is placed on the spider. Once the egg hatches, the paralyzed spider is eaten alive. Some pompilid wasps are kleptoparasites of other pompilids. Basically, they steal the spider prey caught by other pompilid species. These wasps use one of two strategies. They locate the burrow of the host spider wasp, eat the host spider’s egg and then lay their own egg on the spider. The other strategy is to lay an egg on the spider paralyzed by the host wasp during an inattentive moment. The egg of the kleptoparasitic wasp hatches before the egg of the host wasp, which it subsequently eats. In addition to spider wasps, there are two other “unique” wasp pollinator families that warrant the spotlight: fig wasps (family Agaonidae) and pollen wasps (subfamily Masarinae).

Fig wasps

Fig plants and fig wasps have been evolving together for more than 60 million years, and they depend on each other for reproduction. Each fig is formed by a large number of tiny flowers that face the inside of the fig. When female flowers inside the immature fruit are ready for pollination, the fig emits an enticing aroma that attracts only female fig wasps of a species that specifically pollinate that plant species. After locating the fig, the female pushes herself into the fig through the small opening at the end of the fig. The passage is so tight, that the wasp usually loses her wings and pieces of her antennae. She moves around the fruit’s interior visiting many flowers, laying her eggs inside future seeds that will nourish her progeny while spreading pollen collected from the fig where she was born. After laying her eggs, the female wasp dies inside the fig. Once newborns hatch, they mate and generally, the male chews an escape tunnel out of the fig for the females and then dies. The newly-born females collect pollen, and then exit through the tunnel, searching for a new fig tree to lay their eggs, and restarting the cycle. This complex pollen transfer allows all seeds in the fig fruit to grow (these are the crunchy grains in figs that we eat), while providing a safe place for the wasp’s offspring to develop. However, some fig wasps cheat the plant. Instead of entering the fig and pollinating the flowers, these cheaters use their oviposition appendage to pierce through the fig’s green to purplish skin, and inject their own eggs directly into the fig female flowers, exploiting the pollination service of other female wasps that entered the fig to pollinate, without investing energy and doing the work to pollinate the fig. Other non-pollinating fig wasps include gallers, inquilines (animal exploiting the living space of another), parasitoids of fig pollinators and parasitoids of non-pollinating fig wasps. Some of these wasps may directly attack fig wasps inside the fig and eat the larvae or their food (ovary), contributing to the mortality of fig wasp pollinators.

Pollen wasps

Among wasps, the Masarinae or pollen wasps are a peculiar subfamily of Vespidae (Fig. 7). Unlike their vespid wasp cousins, they exhibit the bee-like habit of provisioning each larval brood cell with pollen and nectar. Females of these wasps use their mouthparts to gather pollen and nectar from flowers and for nest construction. Because pollen wasps feed solely on nectar and pollen, they are also known as the “vegetarian” wasps. Relative to this, it is the only wasp group that provisions brood cells with pollen and nectar rather than insects. There are 300 species of pollen wasp across the globe, and the only regions they have yet to be found include the tropics and Antarctica. Even though there is some morphological diversity in the group, most species are brown and black, with contrasting patterns of white, red and yellow.

wasp on purple flower
Fig. 7. Pollen wasp, possibly Pseudomasaris maculifrons visiting Phacelia crenulata. Photo: A. Reeves (CC).

Pollen wasps are unique among wasps, not only because of their diets, but also because of their behavior. In fact, many of their characteristics resemble bees. For instance, like most bees, they are solitary and have long mouthparts, which allows them to reach the nectar of flowers with narrow and deep corolla tubes such as beardtongues (Penstemon). However, unlike many bees who display a corbicula (pollen basket) on their hind legs to transport pollen, pollen wasps collect pollen in their crop (expanded portion of their digestive track that can be used to temporarily store pollen and nectar). Like many bees and wasps, it is the females who are responsible for building the nest, which is hard, made of mud and cemented with secretions from their salivary glands. Nests are usually built in concealed places such as under rocks and crevices, although they may be attached to rocks, ledges, and tree twigs. Similar to many bees, each cell in the nest contains a single pollen-nectar loaf on which an egg is laid, and is sealed with a mud plug. Pollen wasps are known to specialize in foraging on very specific flowers, including beardtongues, borage and tansies, in which they play an important role as pollinators. For instance, a number of rare beardtongue species rely on Pseudomasaris vespoides pollination, giving the insect an important role in maintaining ecological diversity.

Natural pest control

Adult wasps only feed on sugars, which they may obtain by feeding on nectar, honeydew from insects such as aphids, and fruits. However, most wasp species hunt other invertebrates to feed their offspring. Thus, adult wasps do not eat the prey they hunt as they feed it to their young. Despite the fear they sometimes evoke, wasps are extremely beneficial to humans. While searching for nectar, wasps become accidental pollinators, carrying pollen while they travel from plant to plant. However, wasps also serve humans by helping regulate insect pest populations. Relative to this, nearly every insect pest on Earth is preyed upon by a wasp species, either for food or as a host for its larvae. Wasps are so adept at controlling pest populations that the agriculture industry now regularly deploys them to protect crops. A study conducted in Brazil found that social wasps are effective predators that can manage pests in maize and sugarcane. To this point, predatory and parasitic wasps are very valuable natural control agents that help to control insect pest populations in multiple cropping systems. A caveat to this is that one must consider that predatory wasps are generalist predators and, as such, may hunt other beneficial insects such as pollinators, parasitoids, and other predators that may also help control insect pest populations (Fig. 8).

hornet eating fly
Fig. 8. Hornet Vespa Crabro dismembering a syrphid fly. Photo: Paul (CC).

Summary

Wasps do not garner much notoriety as pollinators and are often overshadowed by their bee cousins. Still there are those occasions where wasps are more valuable and efficient pollinators than bees. Additionally, among wasp species are some of the most unique and fascinating pollinators, who sometimes share an intimate relationship with their favorite plants (i.e., orchids). Along this line, are the tiny pollinators of figs who spend most of their life inside a fruit. Without these tiny wasps, many fig varieties commonly consumed may not produce fruits. Further, one should not forget the infamous spider wasps from the family Pompilidae. These wasps are well-known for their viciousness, and ability to subdue spiders much larger than themselves to feed their young (even tarantulas are fearful of spider wasps!). Yet, some of these spider hunting wasps are specialist pollinators of flowers. Though overall, wasps may not be recognized as pollinators, wasp predators and parasitoids have a great reputation for controlling insect pests in multiple cropping systems. For this service, they have earned the praise of farmers and biological control specialists.

Financial support for the publication of this article is via USDA NIFA EIPM grant award numbers 2017-70006-27171

Short Forage, Fall Oats, Winter Forage Options

Jeff Semler, Principal Agriculture Agent
University of Maryland Extension, Washington County

Each year, someone, somewhere, ends the growing season short on forage. There are many more this year. For much of our area, dry conditions are continuing as the jet stream tends to not move for extended periods during the present solar minimum we are experiencing. One area gets dumped on while the other goes begging for water. This has impacted the second (and some areas the first) cutting. Hay crop yields are reported to be down 30 to 40%. The extended days with temperature over 85 F can decrease corn silage yields as corn stops growing above that and we have had many days that fit that picture. Added to it the dry conditions and the potential is for corn yields both be down and later maturity as the corn stopped growing for extended days this summer. It is nearly the beginning of September, and you need to identify how much feed you need and what will supply that. There are still a few options open for last chance forage this year. There are also steps you can take this fall to get very early forage next spring when you run out of haylage. 

If you are looking for high-quality dairy forage, no mechanically harvested crop will produce as much and as high a quality as late summer planted spring oats. Because of the increasingly cool fall temperatures, the forage quality is incredibly high (higher than forage oats in the spring). You may want plant later to wait for the cooler nights to reduce the aphid population which can bring in in Barley Yellow Dwarf Virus. Aphids can infect the plant with BYDV in less than 30 minutes. If you are planting early or on time, it is recommended using a neonic seed treatment as they are effective in limiting aphid feeding, based on research from the Cornell IPM coordinator. A moist fall can hammer this excellent plan by a major outbreak of rust. It could reduce quality and yield. Normally it starts to show a week or so before harvest. If scouting finds it, a highly suggested practice is to apply a fungicide to the oats when they are starting stem elongation. If you have a cereal leaf beetle outbreak an insecticide can be applied at the same time as the fungicide. Both are low cost assurance of top forage yield. 

It is suggested 3 bu/acre of oats. Klicer’s research found NO yield increase from increased fall oat seeding rate. If you use grain type oats, remember it will go through its life cycle quicker and so be ready to plan your timing to dry it for silage. If you are not going to be able to plant until later or have to harvest or graze later, then the slower forage oat type would be the better recommendation based on Ohio State research. Be liberal with the preplant manure but within your Nutrient Management Plan recommendations. In a 2010 study, Cornell studies had a relatively low yield of 2 tons DM/acre due to extremely dry weather. Despite the low yields, over 120 lbs of nitrogen/acre was removed as protein. *NOTE: If you applied manure don’t feed this to dry cows because of high potassium. 

For high producing dairy cows, mow as soon as the flag leaf is out, or early boot. Even early boot is still very good forage. The reason for this is because of the very cool night temperatures inhibit respiration of the most digestible parts, and they accumulate in the plant. As soon as it hits flag leaf, mow wide swath. You are trying to dry something that can yield 2 – 3 times more tons of dry matter than a heavy alfalfa first cutting, compounded by cooler temperatures and much less intensity and hours of sunlight. Even with wide swath, the high yield sheer mass will allow only the top to dry. As soon as the top has a light grey cast (pick up a surface plant and see if it is greener underneath) tedd to get the lower layers spread and drying. Watch forward speed so you don’t make tedder lumps. It is critical that it be ensiled the same day you mow because of the very high sugar levels (exception to rule: if it goes into the 30’s F at night it stops respiration and sugar loss and you can go to the next day). Leaving it overnight in warmer temperatures burns off the sugars and produces higher populations of Clostridia and higher levels of butyric acid. With same-day haylage, these are reduced or eliminated even at higher moisture conditions. On the flip side, the very high sugar levels, if preserved until you ensile the crop; will speed the process and produce an excellent fermented forage if inoculated. 

Fall Spring Oats plus Winter Triticale. This is a triple crop system where oats and winter triticale (100 lbs. oats/acre with 80 lbs. of triticale/acre) are planted after corn silage harvest or in fallow wheat ground. After the oat harvest, the triticale continued to grow and produced an excellent forage the next year. It is CRITICAL that you mow the oats with the cutter bar set at a minimum of 4 inches. Where 4 inches or more is left, the triticale thrived. Where mowed less than 3.5 inches the triticale died. Target flag leaf oat harvest to maximize triticale fall regrowth. Fertilize the triticale as normal the next spring and had an excellent harvest. This can give you two very high-quality forage crops in one planting. 

Last Chance Forage: If it rains, cool-season grasses put on a burst of growth in late August, September, and early October. Feeding the crop with nitrogen and sulfur can give you some very high-quality forage for your dairy herd. It will be wet so chop it ¾ to 1 inch long to reduce leachate. As with the oats above, use a homolactic inoculant and ensile it the same day it is mowed (unless temperatures drop to the 30’s at night). Remember to cut grass at 4-inch cutting height to maintain the stand.

First Chance for Very High-Quality Forage Next Year. Now is the time to get seed for winter forage. This will be the earliest highest quality forage you can get into your cows next spring. Fermented energy levels are equal to corn silage, protein (with sulfur fertilization) can equal good alfalfa. Both rye and winter triticale could be used to produce winter forage. Winter triticale is preferred as it is 35% higher yielding than rye in side by side tests. Flag leaf triticale resists lodging at nitrogen rates over 100 lbs.N/a which gives high crude protein, while rye lodges. 

The Key to High Winter Forage Yields is Planting on Time, which is: 10 DAYS TO TWO WEEKS BEFORE WHEAT-FOR-GRAIN PLANTING DATE IN YOUR AREA. This has proven true over the past 20 years of winter forage research. Earlier planting means more tillers which means more spring yield potential. On-time planting research showed a 25-35% yield increase next spring vs late (same date or later than wheat). 

Should we skip winter forage? NO! Go ahead and plant. You will protect the soil against long term yield-robbing soil erosion; improve the soil health and structure for long term yield gain and still could have economical yields of very high-quality forage. There are several steps that our research has found to improve the yield and survival of late winter forage. Don’t fall for the old story that if you plant late you can make up for it by putting down more seed. Research has not seen any advantage planting over 100 lbs winter triticale seed/acre. If you are forced this year to plant later than the optimum two weeks before wheat grain planting; instead of spending money on extra seed, spend it on having a 3-way fungicide seed treatment applied to the seed. In replicated trials at the on-time planting date, the treated seed yielded 15% more than the control of untreated seed. For the late planting date, the treated seed yielded 28% more than the untreated seed. The late seeding still produced 2.8 tons of dry matter (8 tons/a 35% dm) yield which is a very profitable crop. Much depends on fall weather. The management most critical to survival in late planting is to plant at 1.25 inches at a minimum. If you don’t, in early spring thaw the heaving will push the plant up and they don’t grow. For keys on planting watch the YouTube video Establishing Winter Triticale Forage.

Like cool season grass, oats with an under-crop of winter triticale must be mowed at 4-inch cutterbar height or it will be killed. Mowed properly, this triticale crop is growing very nicely the next spring. 

(adapted from research by Tom Klicer; Cornell University Emertis).

Forage Performance of Cereal Cover Crops in Maryland

Nicole Fiorellino, Extension Agronomist
University of Maryland, College Park

Dairy farmers are constantly looking for sources of forage to meet their feed needs. One source that many of our region’s dairy farmers utilize is the fall planting of cereal grains that are green-chop harvested the following spring. Among the cereal species used for this purpose are rye, triticale, barley, and wheat. Per the Maryland Cover Crop Program guidelines, cereal grains planted as a cover crop prior to November 5 and suppressed via green-chop in the spring are eligible for the grant payment for participation in the Cover Crop Program.  In addition, per the Nutrient Management Regulations, a fall application of dairy manure is allowed to a field planted to a cereal cover crop.

Planting a cereal cover crop that will be green chop harvested fits well into the crop rotation used by many dairy farmers. The scenario that many follow is to plant the cereal cover crop following harvest of corn silage. Prior to planting the cover crop, an application of manure is made to the field. The subsequent planting of the cover crop provides incorporation of the manure into the soil. The fall and spring growth of the cover crop is supplied nutrients from the manure. At the same time, the cover crop provides protection to the soil from loss of nutrients via leaching and/or erosion. The objective of this study was to evaluate select varieties of cereal species for cover crop performance and forage production and quality.

Cereal varieties (21) representing four species (rye, triticale, wheat, barley) were evaluated at Central Maryland Research and Education Center – Clarksville Facility. Three replications for each entry were planted using a randomized complete block experimental design.  Planting date was October 11, 2019. The 3’ X 18’ plots were planted with a small plot planter with 6-inch spacing between each of the 7 rows. The germination percentage for each entry was used to calculate the seeding rate needed to establish 1.5 million seedlings. Good stands were established in most plots by late fall.

Our goal each year is to time spring biomass harvest with when entries reach late boot to early heading stage of development. With the cool spring this year, plant growth and development slowed, with heading delayed until mid-May for most entries (Table 2) and harvest dates varying among the entries (listed in Table 1). Each harvest sample was collected by cutting the plants just above ground-level from three center rows of each plot from an area 2.5 feet in length and from two areas within the plot. The samples were placed into cloth bags and dried using a forced air dryer set at 60o C where they remained until sample water content was zero. Each sample was weighed and is reported as pounds of dry matter production per acre (Table 1). Each of the dried samples was ground through a 20-mesh screen using a large plant grinder and the ground biomass samples were sent to Cumberland Valley Analytical Laboratory for standard forage quality analysis.

Cover crop performance is measured by amount of biomass produced and the concentration of nitrogen (N) in the biomass. These two factors were used to estimate N uptake (Table 2). The cool weather this spring delayed harvest of this study, likely contributing to the higher biomass and N uptake observed this year compared to last year’s trials. There was no significant difference in nitrogen uptake among the varieties tested. A number of forage quality characteristics for these cereals was measured (Table 2). The descriptions of the various quality characteristic are described here and in the footnotes at the bottom of Table 2. Crude protein (CP) is the N content of the forage, with higher protein representing better feed quality. This value was used to calculate nitrogen uptake of each variety (Nitrogen content = % CP/6.25). Both rye varieties and the barley check variety had significantly greater CP than the overall mean, with a number of triticale varieties having significantly less CP content than the overall mean. One rye and the barley variety also had rumen degradable protein (RDP) content significantly greater than the overall mean.

Neutral and acid detergent fiber (NDF, ADF) are measures of feed value and represent the less digestible components of the plant, with NDF representing total fiber and ADF representing the least digestible plant components. Low NDF and ADF values representing increased digestibility; ideally NDF values should be <50% and ADF values should be <35%. Values of both traits were above the ideal this year, as the late harvest resulted in more mature plants. Despite this, four triticale varieties (TriCal EXP 20T02, BCT 15509, BCT 18001, bCT 19005) had significantly lower NDF and ADF values than the overall mean, representing a digestible triticale varieties. This same variety also had significantly higher total digestible nutrients (TDN), net energy for lactation (NEL), relative feed value (RFV), and non-fiber carbohydrates (NFC), indicating good performing varieties.

The characteristic that best captures the overall forage quality performance is Relative Feed Value (RFV). A RFV of 100 is defined as the forage value that full bloom alfalfa would have. In addition to the triticale varieties mentioned previously, one additional triticale variety (TriCal Gainer 154) and the barley and wheat check varieties had RFV values significantly greater than the overall mean.

Though, none of these green-chop cereal forages are considered to be adequate as a stand-alone feed for a dairy operation, they can supply a source of forage used in a total mixed ration at the time of year when feed supply may be running short. When this forage benefit is added to the environmental benefit that is gained, planting winter cereal cover crops on a dairy farm can be a win-win decision.

Download a PDF copy of this report by clicking here

Acknowledgements

This work could not be accomplished without the assistance and oversight of all field operations by Mr. Louis Thorne and Mr. Joseph Crank. We acknowledge the assistance of the undergraduate students who work with Dr. Jason Wight (Shana Burke and Deonna Cousins) for their assistance with seed packaging.

 

Table 1. Average harvest date for cereal species evaluated in Clarksville, MD in 2019-2020.

    Variety Species Average harvest date
TriCal Exp 19R01 Rye May 11
Rye VNS (check) Rye May 4
Mercer Brand Tri-Cow 814 Triticale May 4
TriCal Gainer 154 Triticale May 4
TriCal Flex 719 Triticale May 13
TriCal Surge Triticale May 11
TriCal Merlin Max Triticale May 13
TriCal Thor Triticale May 13
TriCal Exp 20T02 Triticale May 13
TriCal Exp 20T03 Triticale May 13
TriCal Exp 20T04 Triticale May 27
BCT 15509 Triticale May 11
BCT 15513 Triticale May 27
BCT 18001 Triticale May 13
BCT 18002 Triticale May 13
BCT 19003 Triticale May 27
BCT 19004 Triticale May 13
BCT 19005 Triticale May 13
BCT 19006 Triticale May 13
Nomini (check) Barley April 14
P25R25 (check) Wheat May 27

Table 2. Forage and cover crop performance of cereal species evaluated in Clarksville, MD during 2019-2020 growing season.

Variety Species Biomass Yield

lb DM/a

 Head

Date

 1Nitrogen

Uptake

lb N/a

 2Crude

Protein %

 3Soluble Protein

% DM

 4RDP

% DM

 5ADF

% DM

 6NDF

% DM

 7Ash

% DM

 8Total

Digestible

Nutrients

% DM

 9Net

Energy

Lactation

(Mcal/lb)

 10RFV 11Non Fiber

Carb.

% DM
TriCal Exp 19R01 Rye 20655 April 17 395 11.9* 6.7* 9.3 41.8 64.0 7.4 56.5# 0.57# 82.0 15.2#
Rye VNS (check) Rye 20490 May 3 351 10.7* 4.4 7.6* 42.5 65.6 7.4 57.2 0.58 79.2# 14.4#
Rye Mean 20573 April 25 373 11.3* 5.6 8.4 42.2 64.8 7.4 56.9 0.58 80.6 14.8
Mercer Brand Tri-Cow 814 Triticale 23096 April 23 344 9.4 3.9 6.6 39.3 62.4 7.0 59.1 0.60 87.0 19.5
TriCal Gainer 154 Triticale 22925 May 4 260 9.5 3.9 6.7 37.4 59.5 6.6 60.3 0.61 96.5* 22.7
TriCal Flex 719 Triticale 24363 May 13 296 7.6# 2.8# 5.2# 42.7* 64.6 7.2 57.3 0.58 80.0# 19.2
TriCal Surge Triticale 22601 May 13 312 8.5 3.0 5.8 40.8 62.0 7.7 58.2 0.59 85.5 20.1
TriCal Merlin Max Triticale 22618 May 13 295 8.1 3.1# 5.6# 41.1 63.4 8.0 57.3 0.58 83.5 19.0
TriCal Thor Triticale 27172 May 14 357 8.2 3.6 5.9 44.7* 65.3 7.8 55.7# 0.56# 78.0# 17.4
TriCal Exp 20T02 Triticale 23820 May 12 290 7.6# 2.5# 5.1# 34.5# 54.5# 7.0 62.9* 0.64* 106.0* 29.0*
TriCal Exp 20T03 Triticale 24867 May 13 341 8.6 3.0# 5.8 41.6 61.5 8.5* 57.9 0.59 85.3 19.8
TriCal Exp 20T04 Triticale 28459* May 15 343 7.6# 4.0 5.8 48.7* 72.6* 7.4 52.7# 0.53# 65.3# 11.3#
BCT 15509 Triticale 22927 May 14 318 8.6 3.8 6.2 35.3# 56.9# 6.9 62.1* 0.63* 100.5* 25.7*
BCT 15513 Triticale 28316* May 16 358 7.8# 5.0* 6.3 42.6 64.7 6.4 57.1 0.58 80.5# 19.8
BCT 18001 Triticale 25363 May 11 347 8.6 3.4 6.0 37.1# 56.7# 7.7 61.4* 0.63* 98.3* 25.1*
BCT 18002 Triticale 25654 May 12 318 7.8# 3.1# 5.4# 41.6 63.2 6.5 58.4 0.60 84.0 21.1
BCT 19003 Triticale 28526* May 16 329 7.2# 3.8 5.5# 47.4* 70.2* 5.7# 64.2* 0.55# 69.0 15.9#
BCT 19004 Triticale 28740* May 13 366 7.9# 2.8# 5.4# 41.3 62.2 7.0 58.2 0.59 85.0 21.3
BCT 19005 Triticale 24173 May 13 332 8.6 3.0# 5.8 36.6# 57.7# 7.1 61.4* 0.63* 97.5* 24.7*
BCT 19006 Triticale 27915 May 12 330 8.5 3.1# 5.8 36.7# 58.6 7.2 60.7 0.62 95.5 23.9
Triticale Mean 25358 May 12 329 8.3 3.4 5.8 40.3 61.8 7.2 58.7 0.60 87.5 21.1
Nomini (check) Barley 15044# April 23 341 14.2* 6.6* 10.5* 34.4# 55.6 9.0* 61.7* 0.63* 104.2* 19.2
P25R25 (check) Wheat 25376 May 16 189 7.3# 3.7 5.5# 34. 4# 53.7 5.3# 62.7* 0.64* 107.7* 32.4*
Overall Mean 24269 May 10 329 8.9 3.8 6.4 39.9 61.5 7.2 58.8 0.60 88.5 20.8
LSD0.1 3816 2 days – 0.9 0.6 0.7 2.7 3.4 0.8 2.1 0.02 7.5 3.4
*,# Indicates the entry was either significantly greater (*) or significantly (#)less than the overall mean for that feed characteristic.
1Nitrogen uptake (lb N/acre) for each entry was estimated by multiplying the lb DM/ac X % nitrogen contained in the DM. The percent nitrogen for each entry was calculated by dividing crude protein by the conversion factor 6.25 which is the average amount of nitrogen (%) contained in protein.
2Crude Protein %: represents total nitrogen content of the forage; higher protein is usually associated with better feed quality.
3Soluble Protein %: non-protein N and portion of true proteins that are readily degraded to ammonia in the rumen.
4RDP (Rumen Degradable Protein): portion of crude protein that microbes can either digest or degrade to ammonia and amino acids in the rumen.
5ADF (Acid Detergent Fiber): represents the least digestible fiber portion of forage; the lower the ADF value the greater the digestibility.
6NDF (Neutral Detergent Fiber): insoluble fraction of forage used to estimate the total fiber constituents of a feedstock.
7Ash: mineral elements of the forage.
8TDN (Total Digestible Nutrients): measure of the energy value of the forage.
9Net Energy Lactation: estimate of the energy in a feed used for maintenance plus lactation during milk production.
10RFV (Relative Feed Value): indicates how well an animal will eat and digest a forage if it is fed as the only source of energy.
11Non Fiber Carbohydrates: represents all forms of digestible carbohydrates (starch, sugar, pectin, and fermentation acids) in the forage.

Table 3. Brands and companies in the 2019-2020 Maryland cereal forage trials.

Brand Address
Eddie Mercer Agri-Services, Inc. 6900 Linganore Road

Frederick, Maryland 21701

www.eddiemerceragri-services.com
Seed-Link Inc. 208 St. David Street

Lindsay, Ontario (Canada) K9V-4Z4

www.seed-link.ca
TriCal Superior Forage 12167 Highway 70S

Vernon, Texas 76384

tricalforage.com

Ant Influences on Pollination and Some Other Plant Services

$Associate Professor and Extension Specialist, CMNS, Department of Entomology
*Assistant Professor, CMNS, Department of Entomology. Twitter: @Analyssi

Note: This is the sixth article of our series on pollinators. The initial articles can be found in the vegetable and fruit headline news June, July and August special editions and Maryland Agronomy News Blog.

Introduction

Ants (Hymenoptera: Formicidae) are among the most evolutionarily successful insect groups. They are prevalent numerically, geographically and ecologically, and subsequently have an extreme impact on the various ecosystems that they inhabit. Ants are the largest insect family in terms of species diversity and sheer number of individuals. More than 15,000 species of ants are known globally. Though they are notoriously recognized as generalist foragers, some ant species regularly visit flowers (Fig. 1). Similar to numerous other insects, ants enjoy eating energy-rich nectar and frequently visit angiosperms flowers. Further, ants are close relatives of other hymenopterans (bees and wasps) which are important pollinators in most plant communities. However, comparative to their relatives, ants are mostly minor pollinators and can even have an antagonistic relationship with flowers. It can be at first viewed surprisingly that the number of ant-pollinated plants is low considering their abundance, the fact that they can carry pollen, and that they commonly visit flowers. Though two thirds of all angiosperms are pollinated by insects, roughly 30 reports suggest pollination by ants. However, this may be an overestimation, as experiments have not been conducted to confirm ant pollination in all reported cases. Ant pollination is thus rare and restricted to a few species within different families of angiosperms. Several reasons have been proposed to why ants are poor and rare pollinators. One is that due to their small size, ants can extract nectar without touching the reproductive organs of flowers, thus not contributing to pollination and consequently acting more like nectar robbers than pollinators. Another reason lies in the morphology and chemical characteristics of the body surface of ants. Their bodies are smooth and hairless making it hard for pollen to attach to ants. Further, their body surface secretes antibiotics secretions, which have been shown to reduce the viability of pollen grains. Moreover, their mandibles are not ideal for nectar collection, and are rather destructive to flower parts. Although ants are rarely considered true pollinators, there are instances where they can serve as pollen vectors as well as contribute to other ecosystem services through other mutualistic interactions with plants.

Ant on a flower
Fig. 1. Florida Carpenter Ant, Camponotus floridanus collecting nectar from a black mangrove blossom. Photo: B. Peterson (CC).

Ants importance as pollinators

Many ants visit flowers that are also visited by other insect pollinators (Fig. 2). When doing so, and depending on the floral morphology, pollen grains can attach to their bodies. However, for reasons stated above, their contribution to pollination is not remotely as important as other invertebrate pollinators such as beetles, flies, butterflies and moths. Relative to this, ants are not considered important pollinators and ant pollinators are believed to be extremely rare. However, ants may play a role in pollination under a limited set of circumstances such as in situations where smaller plants (epiphytes or annual herbs) occur in high density. For example, the knotweed Polygonum cascadense, a small, apparently self-incompatible annual, was determined to be regularly cross-pollinated by the ant, Formica argentea (Figs. 3a, b). Ant pollination may also be essential when more effective winged pollinators are scarce and ants contribute to enhance self-pollination such as in arid or alpine environments. Further, there are situations where pollination by ants are comparative to that of bees. For instance, studies indicated that ants significantly contribute to seed set of the shrub Conospermum undulatum. Further, pollen of this and other Conospermum species have a germination rate of ~80% after contact with ants, which equals that of bees. This is relevant because these investigations showed that other plant species showed a significant reduction in germination rate (to about 10%) following ant exposure. This indicates that the pollen of Conospermum is resistant to the ant’s antibiotic secretions. Given this, it is likely that Conospermum has evolved to become successfully pollinated by ants.

bublebee covered in pollen on flower
Fig. 2. A bumblebee with pollen and an ant exploring a hibiscus flower. Photo: D. Lundy (CC).

There are instances where pollen exhibits reduced germination after ant exposure, yet the abundance of ant visitation leads to increased number of viable seeds in plants that they visit. In this case, the loss in pollen germination is made up by the frequency and number of flower visits. This is the case for worker ants (Proformica longiseta). In a study of the flowering woody plant Hormathophylla spinosa, even though flowers were visited by 38 species of winged insects, worker ants maintained the strongest mutualistic interaction. The key factor was thought to be the large crowd of workers visiting H. spinosa throughout its flowering period. In relation to this, it is important to realize that ants being social insects, individual colonies can contain millions of members, which have the potential to increase floral visits to extraordinary numbers. Thus, floral visit inefficiencies can be made up with large number of visits.

Figs. 3. a) Polygonum cascadense and b) Photo: a) B. Miller and b) B. S. Lindgren (CC).

Ant pollination traits

Ant-pollination syndrome may be defined as flower characteristics or traits that are associated with ant pollination. Common traits of ant pollination include low-growing or small plants that occur in high density or in groups, and mostly prostrate in growth form with closely intertwined branches. Flowers are generally small and brightly colored, or white with an open structure that grants access to floral nectar. Ants also seem to be attracted to inconspicuous and sessile flowers that are low-growing, positioned close to the stem, and exhibit minimal attractions. Ant pollinated flowers also have relatively few ovules, which may all be pollinated by compendious pollen deliveries. Ant flowers produce small amounts of sticky pollen grains so as to not stimulate self-grooming which removes pollen load, and to effectively attach to the often-smooth ant body surface. Similarly, nectaries are small and morphologically available to flightless ant workers, and produce low quantity of nectar so that larger insects are not interested. Ant plants often contain overlapping inflorescences at a uniform height, and low seed number per flower, which requires reduced pollen transfer.

Most plants displaying ant‐pollination syndromes appear to occur in hot and dry, or alpine habitats where ants are abundant and active. Examples include plant species occurring on the hot dry slope of the western Cascades of Oregon, granite outcrops of the southeastern US and the Colorado alpine tundra. Some examples of ant-pollinated plants in North America include the small’s stonecrop (Diamorpha smallii), the alpine nailwort (Paronychia pulvinata) and the Cascade knotweed (Polygonum cascadense; Fig. 3a). Ants were also shown to be significant pollinators of two orchid species (Chamor-chis alpine and Dactylorhiza viridis) in the alpine zone of the Alps. Speaking of orchids and ants, the Australian orchid, Leporella fimbriata is pollinated via pseudocopulation. In this case, a male ant is attracted to the flower, which visually and chemically resembles the female of the ant species. Once the male lands on the flower, he tries to mate, and while doing so he unwillingly receives and transfers pollen. In the case of L. fimbriata, winged males of the bulldog ant genus Myrmecia mistaken these flowers for virgin queens and attempt to mate with them, picking up pollen in the process (Fig. 4).

flying ant with wings
Fig. 4. Flying male, Myrmecia urens on hare orchid, Leoorella fimbriata. Photo: ron_n_beths pics (CC).

Why are ants inefficient at pollination?

Biochemistry. Ants usually live underground in humid conditions, and often in association with fungal and bacterial colonies that they actively cultivate and tend to. To avoid being exposed to infections, ants and their larvae secrete antibiotic materials to suppress bacterial and fungal growth on their bodies. These secretions have been shown to interfere with pollen germination, by killing pollen grains that come in contact with ant secretions while they are foraging. Because antibiotic production is central to ant survival, the evolution of this disease resistance trait in ancestral ants may have limited the ability of ant pollination to evolve broadly among flowering plants.

Body traits. Ants are usually small, especially compared to alternative insect pollinators. This small size reduces the amount of pollen an individual ant is able to carry. Moreover, their diminutive stature allows them to avoid contact with anthers and stigmas while getting nectar from flowers, and at least in some ant species, pollen may not be able to properly adhere to their hard and generally smooth bodies. Even though this is the case for most ant species, many others can be as hairy as bees, or are covered with bristles suitable for carrying pollen.

Behavior. Ants may interfere with pollination by damaging plants’ reproductive organs with their large mandibles, and by removing pollen from their body while self-cleaning. Ants may also be more attractive to extrafloral nectar of plants as opposed to their flowers. However, it is probable that plants lure ants towards their extrafloral nectaries in part to prevent them from damaging their flowers (Fig. 5). Extrafloral nectaries are nectar-secreting organs, which supply insects with carbohydrates while maintaining them away from the reproductive organs. In the case of ants, it is possible that this organ evolved to distract ants from flowers, and to attract worker ants who function as bodyguards for these plants. It has been also suggested that the wingless ant workers who visit many flowers are unable to carry pollen far enough for outcrossing, since they continuously revisit the same plant for nectar. Relative to this, a large majority of ant-pollinated plants are self-compatible (capable of self-fertilization) and are thus less affected by geitonogamy (pollination of a flower by pollen from another flower on the same plant). This indicates that the evolution of ants as pollinators may have been only (or mostly) possible in plants that do not require long-distance pollen dispersal.

dark color ant on leaf
Fig. 5. Ant collecting nectar from an extrafloral nectary of Inga sp. plant. Photo: A. Kay (CC).

Plant defenses. Ants are more popularly known as nectar thieves or robbers. This is because they remove nectar from plants without effectively pollinating their flowers. Because of their thieving nature and the potential damage that they can cause to flowers, numerous plants have evolved barriers to exclude ants from their floral rewards, such as dense fields of hairs or sticky bands inside their corolla. Some plants also employ ant-deterrent mechanisms to prevent disruption of pollination. These mechanisms include morphological features that promote ant and floral spatial segregation or ant-repellent volatile compounds in petals and/or pollen. As such, repellency of floral parts, sticky tissues and glandular hairs may further limit ant’s access to flowers.

Negative floral visitation costs

In addition to pollination failure, floral visitation by ants can result in several other non-positive outcomes. Their visits may result in damaged floral structures, reduced pollen viability, avoidance by other pollinators in response to ants and their olfactory cues, and exploitation or alteration of floral resources. Further, floral visitation by ants can reduce plant reproduction success in situations where ants harass and interfere with more effective pollinators. Relative to this, a study was conducted to examine the importance of floral visitation by the non-native Argentine ant (Linepithema humile) on island morning glory (Calystegia macrostegia ssp. macrostegia). The Argentine ants often behaved aggressively towards other floral visitors. Consequently, their presence in morning glory flowers disrupted pollination services by decreasing floral visitor diversity, bee visitation rates and pollen levels. In other situations, honeydew‐producing insects such as aphids, scales and mealybugs may alter the activity and density of ants on plants, which, in turn, can disrupt pollination services. Ants feed on honeydew produced by these insects and in turn protect them from their natural enemies and impede visitation by true pollinators. Pertinent to this, another study involving Argentine ants was conducted in which the number of cotton aphids, Aphis gossypii was manipulated on cotton (Gossypium hirsutum) plants. The study showed that increasing aphid numbers enhanced ant abundance on cotton plants and their floral visitation. Consequently, the duration of visits by honey bees and seed production declined as a result. These studies illustrate that ants can intimidate pollinators, interfere with pollination and subsequently abate plant reproduction.

Other ant services to plants

Plant visitation by ants can in some circumstances benefit plants. In addition to rare cases involving ant‐mediated pollination, ants may interact with other floral visitors in ways that deter ineffective floral visitors in favor of effective pollinators, or potentially enhance the male component of plant fitness by increasing pollen transfer. Further, though ant’s contribution to pollination services is minimal, there are two other central ecosystems services that they contribute to in plants: seed dispersal and plant protection.

Seed dispersal – Ants play a key role in seed dispersal in many ecosystems and there are numerous ant species that remove and transport seeds. Seed dispersal by ants (myrmecochory) is a global driver of plant diversity and population dynamics. Myrmecochorous plants dominate communities in many habitats, and are characterized by the presence of a lipid-rich structure (the elaiosome) that is particularly attractive to ants. Though, long-distance seed dispersal can occur via ants, they generally disperse seeds only short distances to their nests, where they remove the elaiosome to feed it to their larvae. Until today, elaiosomes have been found in over 11,000 plant species across 77 flowering plant families. Similar to pollinators, seed dispersers are essential to plant diversification and colonization of new habitats. To this point, myrmecochorous dispersal is a reliable means of seed propagation. Myrmecochory allows plants to increase their area of distribution and success at progeny establishment.

Plant protection – Through mutualistic interactions, ants help protect plants from being eaten by insect and vertebrate herbivores. In these cases, plants rely on the defensive capabilities of ants to protect them from insects, including nectar robbers. In this type of interaction, the ants receive access to a high-quality food source, while the plant receives protection against herbivore colonization and feeding. Ants may also prune climbing vines and prevent fungal and microbial infestation on plant tissues. Thus, the establishment of this mutualistic interaction enhances the reproductive success of plants with extrafloral nectaries, and this strategy has thus evolved multiple times throughout the history of flowering plants. In order to protect the nectar source, ants attracted to extrafloral nectaries are usually defensive against other plant visitors. Further, it has been shown that the larger the value of the extrafloral nectar to ants, the greater their aggressiveness toward herbivores. To this point, some ant body guards may even consume herbivorous arthropods that they encounter on plants; and it has been shown that some ant species can reduce crop pest numbers and their damage, resulting in greater crop yields. Indeed, because of their large numbers, ants have the capability to rapidly consume large number of insect pests. It has been suggested that their efficiency as pest suppressors is comparable to chemical pesticides or higher, while at lower economic and environmental costs. To this point, ant predation contributes to the natural suppression of economically important insect pests. An example of this is weaver ants of the genus Oecophylla, where it has been shown that they can be highly efficient biological control agents (Fig. 6).

Two ants pulling apart an insect prey
Fig. 6. Weaver ants, Oecophylla spp playing tug-of-war with their prey Photo: Moushomi, B.C. (American Museum of Natural History – Facebook).

Summary

Ant-plant associations are immensely diverse and present globally, leading to both mutualistic and/or antagonistic interactions. Regarding ant–plant mutualism, ant pollination is considered to occur with rarity and few studies have explicitly explored ants’ roles as pollinators. Ants, unlike other insect pollinators have several impediments such as limited foraging distances as most are wingless, and they produce body secretions that reduce pollen viability. Though ant-pollination is insignificant when compared to other invertebrate pollinators, there are instances where other pollinators are absent or scarce such as in alpine and arid conditions, where plants rely on foraging worker ants for reproduction. Along with pollination, ants play a key role in seed dispersal in thousands of plant species, which is key to plant diversification and colonization of new habitats. Last but not least, ants are also capable of protecting plants from herbivory and expelling nectar thieves, which is many times facilitated and promoted by the presence of extrafloral nectaries. This leads to higher reproductive success and fitness, which in the case of economically important plants is reflected in greater yields and enhanced crop quality.

Financial support for the publication of this article is via USDA NIFA EIPM grant award numbers 2017-70006-27171.

August 2020 WASDE Report

Dale Johnson, Farm Management Specialist
University of Maryland

 

Information from USDA WASDE report

Attached is the summary for the August 12 WASDE.

Corn

There was an adjustment of a minus 20 million bushel to the 2019/20120 crop estimate which carried forward to the beginning stocks of the 2020/2021 crop year. Yield estimates for the 2020/21 crop year were adjusted up from 178.5 bushels per acre estimated in July to 181.5 bushels per acre current estimate. These two changes resulted in an increase of 258 million bushel in estimated 2020/21 supply. On the demand side, feed & residual and export estimates were increased by a total of 149 million bushel. The resulting estimate of ending stocks was increased by 108 billion bushel increasing the Ending stocks to use ratio to 18.7% from 18.1% in July. These bearish numbers continue to suppress prices. Futures market prices have been in decline since the up tick in prices at the end of June/beginning of July so today’s WASDE report had little effect on prices and December corn settled at $3.27 per bushel.

Soybeans

There was a slight decrease of 5 million bushel to the 2019/20120 crop estimate ending stocks  which carried forward to the beginning stocks of the 2020/2021 crop year. Yield estimates for the 2020/21 crop year were adjusted up from 49.8 bushels per acre estimated in July to 53.3 bushels per acre current estimate. These two changes resulted in an increase of 285 million bushel in estimated 2020/21 supply. On the demand side, the crushing estimate was adjusted up 20 million bushel, export estimate was adjusted up by 75 million bushel and residual was adjusted up by 5 million bushels.  The resulting estimate of ending stocks was increased by 185 million bushels increasing the Ending stocks to use ratio to 13.7% from 9.8% in July. Just like corn, soybean futures market prices have been in decline since the up tick in prices at the end of June/beginning of July so today’s WASDE report had little effect on prices and November soybeans settled at $8.83 per bushel.

Wheat

There were minor adjustments in wheat supply and demand resulting in a 17 million bushel decrease in ending stocks estimate decreasing the Stocks-to-use ration from 45.6% in July to 44.3% in August. There was little movement in wheat prices and September 2020 SRW prices settled at $4.90.

Webinar: Starting a Farm in Maryland

We are excited to announce the launch of the new Agricultural Careers and Entrepreneurship (ACE) Virtual Center! This website has been designed to help connect MD residents interested in agriculture with career and entrepreneurship opportunities. More specifically, the ACE Center provides resources to online training, information about agriculture in Maryland, job search advice, networking and more.

We are celebrating this new website by offering an ACE Virtual Webinar Series. Any aspiring or beginning farmers are encouraged to join us for our webinar – Starting a Farm in Maryland. This event will be led by Shannon Dill, Ag Extension Director on Tuesday, August 18th, 2020 @ 1:00 pm.

You can register in advance for this virtual webinar using the following link: https://umd.zoom.us/meeting/register/tJMucuisrDMtGd2qw-pHND4-QZ9JDv61_9bB

More information on the webinar series can be found on the homepage of the ACE Center. 

Maryland Regional Crop Reports: August 2020

Reports are for crop conditions through August 6, 2020.

Western Maryland

Recent rains have helped replenish soil moisture to a point but only time will tell if it helped our crops. Corn yields will certainly be reduced by the hot dry weather we experienced this year. Full season soybeans may fare a little better than the corn but we will have to wait and see. Double crop soybeans are struggling and without additional significant moisture will most likely be disappointing. A greater proportion of our corn crop will be headed to the silo and not the grain bin as dairymen stock up their winter stores. Hay stocks are also down so savvy operators will be planting oats and winter cereals for increased forage reserves.—Jeff Semler, Washington Co.

Central Maryland

Much needed rain came with Hurricane Isaias this week, with most of the region seeing approximately 2-4 inches of rain, according to the National Weather Service. I have not heard any reports of major flooding in the area. Corn has been more affected by the dry weather, with most lower leaves completely dried up. Corn silage harvest will begin soon. The corn earworm, fall armyworm, and western bean cutworm traps have caught very low or no moths this summer, indicating low populations this year.—Kelly Nichols, Frederick Co.

Northern Maryland

Rain has been sporadic and isolated from approximately the first week of June through the third week of July. It is not common on our soil types here to see hard leaf roll in corn, but you didn’t have to look hard to find it in July. All things considered, crops do not look that bad, as timely storms right around corn pollination likely saved yields. You can find incomplete pollination in corn on lighter soils, but overall, yield potential is still good in most fields, but likely not as big as the past few years. The hurricane brought some much-needed 2-5 inches of rain. Double crop soybeans are growing slowly and sill very short. Full season soybeans look pretty good; although many fields have reduced pod set due to the lack moisture. Recent rains should help compensate for fewer pods by making bigger beans and maybe a few more blooms. Disease pressure in both corn and soybeans has been minimal.—Andy Kness, Harford Co.

Upper & Mid Eastern Shore

With the recent 3-6” of rain, most of the region will probably have record drylands corn yields. Irrigated corn looks good, but the cloudy humid weather for the past month may have shaved some top end potential off. Gray leaf spot is sporadic with infection levels all over the board. Early corn is dented. Full season soybeans are taller than I like to see with many beans reaching 4’; well at least before the hurricane. Due to lodging, some are now 2’ tall. Double crop beans have closed over the rows. Hay yields have continued to be above average, but it has been a challenge to get it cured. Many acres of corn have been sprayed with a fungicide. Herbicide resistant weeds continue to be a problem in soybeans. And there have been a few bean fields with worms at thresh hold levels requiring treatment. Hopefully the hurricane didn’t deliver rust spores from the south.—Jim Lewis, Caroline Co.

Lower Eastern Shore

After having a dry spell, we have finally had several rain events on the Lower Shore, and crops are looking much better. Early season corn will likely have yield loss due to the dry weather during critical growth periods. Some corn is already in dent growth stage, approaching maturity. Soybean crops are looking promising, and double-crop beans are getting a good start. Palmer amaranth is present on many farms in the area, anywhere from early vegetative growth stages to already flowering. Common ragweed is also prevalent, including young seedlings, which is surprising as ragweed is primarily a spring emerging weed. Hurricane Isaias swept through the area yesterday, which brought 1 inch of rain in Salisbury and reports of up to 3 inches in other locations. There were reports of three tornados that touched down on the Lower Shore. As of yet we have not gotten reports of major crop damage from high winds.—Sarah Hirsh, Somerset Co.

Southern Maryland

With regular rains over the past month, most corn and soybean crops have been in good to excellent condition. Most grain sorghum fields are headed out and sugarcane aphids are starting to show up in low numbers, though headworm pressure seems to remain low at the time. The area saw between 2 to 10+ inches of rain from the tropical storm that moved through on Aug 4, with much of the heavier rain to the south and east. High winds saw some blowdown of soybean crops, which should recover. More damage is expected to be seen in vegetable crops, especially where heavy rains and standing water will likely lead to disease problems through the rest of the season.—Alan Leslie, Charles Co.

 

Preliminary Trial of Clove Oil-Based Herbicide for Cover Crop Termination in Organic Farming

Ray Weil1, Kevin Conover2, Mia Godbey1
1Dept of Environmental Science and Technology and 2Central Maryland Research and Education Center
University of Maryland, College of Agriculture and Natural Resources

Weed control is almost invariably cited as one of the biggest challenges for the organic production of grain crops. Synthetic herbicides cannot be used in organic farming, leaving tillage as the main weed control option. Tillage is also the main method of terminating cover crops in organic farming, although roller-crimping can work under some circumstances. The lack of chemical means of weed control makes low disturbance or no-till organic farming extremely difficult if not impossible on a commercial scale.

This spring we conducted a preliminary trial to access the efficacy of a new organically-approved herbicide called Weed Slayer® (based on Eugenol, an essential oil from cloves, molasses, and a biological surfactant mixture). This product comes in two parts, the Clove Oil product, and the microbial surfactant product, that must be mixed together in equal parts.  The manufacturer, Agro Research International, recommends a rate of 1-3 quarts/acre of each part in 20-25 gallons water/acre.

We established a cover crop stand that initially included 12 species (originally 4 legumes, 4 brassicas, and 4 kinds of grass) planted in fall 2019, but because of the very dry conditions in August-October 2019 and winter killing of the radish, we ended up with a few plots of good cover crop biomass (>3,000 lbs/acre dry matter) consisting of mainly red, white and crimson clovers, hairy vetch, annual ryegrass, and cereal rye with the occasional turnip or kale. The covers were allowed to grow into full flowering. On May 27, soybeans were “planted green” in and the plots were sprayed with three herbicide treatments: 1) RU: the normal rate of Glyphosate, 2) WS1: the recommended rate of 1 quart/acre each part of Weed Slayer®, and 3) WS2: a rate of 2 quart/acre rate of each part of Weed Slayer® (Figure 1).

field showing burndown herbicide treatments
Figure 1. Appearance of sprayed multi-species cover crop plot 7 days after treatments were applied.

We used the Canopeo app (canopeoapp.com) to measure the green cover percentage at 2 and 7 days after spraying at 6 locations within the tire tracks and within the untracked middle area of each plot. On day 7 we also measured the green cover of the unsprayed cover crop at the edge of the field (to serve as a control). We did this in two blocks about 80 feet long and 45 ft wide. At four weeks after spraying, visual observations were made to access any possible regrowth of the cover crop.

Results. Two days after spraying, the effect of the tractor tire tracks was quite evident, with less remaining green foliage in the tracks than in the untracked middle rows of the plot (Figure 2). In the untracked area, the 1 quart/acre rate of Weed Slayer® had about 25% green area remaining, which was greater than the 18% green area for the Round-Up and the 2-quart rate of Weed Slayer®. In the tire tracks, less than 10% green area remained for all three treatments.

Figure 2. Percent green (living foliage) area two days after herbicide treatments were sprayed on multi-species cover crop. Measurements were made in the tractor tire tracks (right) and in the untracked middle row (left) of the plot.

By the 7th day after application, there was no difference among the three spray treatments in green cover in the tire tracks where the only detectable green foliage was that of the emerging soybean seedlings (data not shown). There was also very little difference in the untracked middle of the plot with Round-Up and Weed Slayer®2X  exhibiting statistically the same percent green area (Figure 3), which was almost entirely due to the emerged soybean seedlings. The Weed Slayer® 1 quart/acre rate had about 5% green area, which was statistically greater than the Round-Up plots, and about half due to cover crop and half to soybean seedlings. The grasses were killed earlier than the legumes by both herbicides, but by day 7 all cover crop species appeared to be nearly completely killed. Most of the green cover by day 7 was due to the soybean seedlings. However, visual inspections four weeks after the spray treatments revealed some re-growth of the hairy vetch in the Weed Slayer® plots but not in the Round-Up plots. No grass regrowth was observed.

Figure 3. Percent green (living foliage) area seven days after herbicide treatments were sprayed on multi-species cover crop. Measurements shown are for the untracked middle rows (right) of the plot.

Weed Slayer® currently costs about $60/acre for the 1 x rate (purchased online in a package of 1 gallon of each part). This is expensive by conventional grain production standards, but feasible for organic grain which brings about twice the price per bushel as conventional. An affordable, effective organic-certified burn-down herbicide for grassy species (and some broadleaves) could open up important opportunities for no-till and cover cropping practices not currently practical in organic farming.

 

Key Steps for Optimum Forage Establishment

Amanda Grev, Pasture & Forage Specialist
University of Maryland Extension

Last month we discussed strategies for assessing pasture stands and some initial considerations when beginning to think about pasture renovations. Now that August has arrived, if you have decided to proceed with some form of pasture renovation this fall it will soon be time for planting. Regardless of the extent of your renovation, there are several steps you should follow to make sure the seeding process goes smoothly. Below is an overview of the key steps necessary for optimum forage establishment.

Step 1: Correct Soil Fertility

Poor soil fertility is one of the most common causes of poor stand establishment and also poor stand persistence over time. Acidic conditions (low soil pH) will reduce nutrient availability and impair root growth and development, and essential nutrients like phosphorus are critical for proper seedling development. Because of these effects on plant nutrient availability and utilization, ensuring adequate soil pH and fertility is essential for optimum stand establishment and to obtain persistent, high-yielding stands long term. Soil fertility testing should be done prior to renovation so that lime and fertilizer can be applied according to soil test recommendations.

Step 2: Control Weeds

Weeds compete with desirable forages for light, nutrients, moisture, and space and can shade out or outcompete new seedlings. For best results, ensure weeds are controlled prior to seeding. Remember that while herbicides can be a useful tool for weed management, they are not the only option for weed control. An integrated approach that combines various cultural, mechanical, and chemical control practices will be the most successful.

Step 3: Select Adapted Species

Not all forages will perform equally on different sites, so be sure to select forages that are well suited for your soil and site characteristics. This includes variables such as soil type, drainage, moisture holding capacity, pH, fertility, and topography. For example, species such as orchardgrass or alfalfa require a higher level of fertility and will not thrive in systems with low soil pH or poor soil fertility. Be sure to select forage species that will match your intended use (hay vs. pasture, perennial vs. annual, time of year, management system) and livestock requirements based on species, age, and life stage.

Step 4: Inoculate Legume Seeds

If you plan to incorporate a legume as part of your forage mix, be sure the seed is properly inoculated with nitrogen-fixing bacteria. Some legume seeds come pre-inoculated, which saves time and helps to ensure inoculation. If not, be sure to select the appropriate inoculant strain depending on the legume species and inoculate the seed with fresh inoculant prior to seeding using an effective adhesive material to hold the inoculant on the seed. Inoculants are living organisms and will only work if the bacteria are alive when applied, so be sure to use proper storage and handling and check expiration dates.

Step 5: Graze and/or Clip Close

Grazing or clipping a pasture close to ground level prior to seeding will help eliminate residue and assist in suppressing competition from existing vegetation, giving new seedlings an opportunity to grow. If using livestock to accomplish this via grazing, be mindful of the potential effects this may have on animal performance, including the consumption of lower quality forage and/or the potential for increased parasite loads as animals graze below the usual minimum height recommendation.

Step 6: Prepare a Proper Seedbed

This step will vary slightly depending on the use of tilled vs. no-till seedings. If using tillage, be sure the seedbed is soft yet firm following tillage. An underworked seedbed will have too much surface residue and will be too rough for good seed placement, while an overworked seedbed will be too fluffy and fine and will dry out quickly. A good rule of thumb is that your boot tracks should be around ¼ inch deep. For no-till seedings, it is especially important to suppress the existing stand and reduce residue prior to planting. In addition to close grazing and/or clipping, the existing stand can be suppressed using a nonselective herbicide.

Step 7: Seed at the Proper Depth

Seeding too deep is one of the most common causes behind establishment failures. Be sure the seed drill is calibrated appropriately so that seed is placed at the proper depth. Take into account your soil type, texture, and moisture conditions; in general, seed should be placed slightly shallower in a heavier soil with a higher moisture content and slightly deeper in a lighter soil with lower moisture content. For most cool-season forages, the ideal seeding depth is ¼ to ½ inch, but seed characteristics vary so be sure to determine the optimum depth and adjust accordingly prior to planting. The key is to provide good seed to soil contact without placing the seed too deep.

Step 8: Seed at the Proper Time

Cool-season forages can be seeded in either the spring or late summer. Advantages of late summer seedings generally include reduced weed competition and cooler weather conditions during establishment. The ideal time will vary depending on your location and weather conditions but in general, the optimum time for late summer seeding in Maryland occurs from mid-August through mid-September.

Step 9: Seed at the Proper Rate

Similar to seed depth, calibration is essential to achieve a proper seeding rate. Seeding rates will vary based on forage species selection, be sure to follow recommendations when making seeding rate decisions. Pasture seeding rates are typically higher than hay seeding rates to provide a denser sod for grazing. Seeding rates can be adjusted slightly based on conditions at the time of seeding. If conditions are optimum, seed at the lower end of the recommended range. If conditions are poor, seed at the higher end of the recommended range.

Step 10: Manage New Seedings During Establishment

New seedings are especially sensitive during their establishment year. To maximize success, delay grazing on newly seeded areas until sufficient root systems have been developed to prevent livestock from uprooting newly established plants when grazed. Avoid grazing new stands during extremely wet periods, be very careful not to overgraze, and continue to scout for weeds or other potential issues that can impair establishment.

 

In Dry Weather, Watch for Silk-Clipping Insects in Corn

Maria Cramer, Galen Dively, and Kelly Hamby
University of Maryland, Department of Entomology

It is not unusual to see groups of Japanese beetles feeding on corn silks, which is known as “silk clipping” Figs.1 and 2). While Japanese beetle numbers tend to peak in July, there are multiple beetles that may clip corn silks, and with later maturity field and sweet corn silking in August, it is important to still be on the lookout But how much of a concern is silk clipping, what should you be looking for, and what should you do about it?

japanese beetles on corn silks
Figure 1 (left). Japanese beetles feeding on corn silks. Figure 2 (right). Silk regrowth after clipping. Images: M. Cramer, University of Maryland

Silk clipping is often not as much of a concern as it initially appears. If silks are clipped after pollination, which occurs within the first 4-5 days of silk emergence1, kernel set will not be affected2. If clipping reduces the number of kernels, the kernels may develop to be larger and offset the reduction in number2. However, under drought conditions, yield loss from silk clipping is more likely2,3.

Drought slows silk emergence and pollination, which means there is a longer window where silk clipping can hurt yield. Indeed, severe drought stress can cause incomplete silk emergence and cause a mismatch between pollen shed and silks that results in nearly blank cobs1. Drought can also make it harder for plants to compensate for poor pollination1. If leaf rolling begins in the early morning and continues until evening1, the field is stressed enough to be of concern and it is important to scout for silk clipping beetles during the first several days of silk emergence.

The culprits. Japanese beetles are the most noticeable silk clippers in Maryland because they are large, shiny, and congregate in groups (Fig. 3). They are a sporadic pest4 and their populations will vary yearly. However, their populations may be higher in corn following sod, soybean, or perennial ryegrass or clover covercrops4. Other beetles that may clip silk include the western, northern, and southern corn rootworm adults (Fig. 4)5. Western corn rootworm (WCR) has several look-alikes that do not clip silks, so make sure check the stripes; WCR will not have crisp black stripes, but instead has smudged stripes.

japanese beetle and other beetles on corn
Figure 3 (left). Japanese beetle. Image: E. Hodgson, Iowa State. Figure 4 (right). Adults of southern corn rootworm (left), western corn rootworm (middle), and northern corn rootworm (right). Image: Varenhorst, South Dakota State 

Scouting. Silking typically begins 3 days after tasseling5, so plan your scouting accordingly. You want to evaluate the silk stage and pollination. Silks naturally senesce about 10 days after emergence, browning and drying out. At this point, pollination can no longer occur1. To determine if green silks have been successfully pollinated, you can dissect the ear and do a shake test. Pollinated silk starts to discolor and drop away at the base of the silk where it attaches to the ear. Bob Nielson with Purdue Extension has produced a great video describing the pollination shake test: https://www.youtube.com/watch?v=K7DiwD4N0T0&feature=youtu.be

You should scout if pollination is incomplete. When scouting, make sure you sample both the edges and the interior (at least 40 feet into the field); while you may see alarming numbers of Japanese beetles on the edge of the field, there are usually much fewer inside the field2. Sample a minimum of 20 corn plants in 5 locations spaced evenly though the field. Count the number of beetles per ear and measure the length of the silks.

Thresholds. For Japanese beetles, three conditions need to be met to before an insecticide application will pay off: 1) there are three or more beetles per ear, 2) silks are clipped to less than ½ inch in length, 3) and pollination is less than 50% complete4 (most silks in the field are still green and/or shake test indicates about half of the silks are still attached). Conditions are similar for rootworm beetles, but the threshold is five or more beetles per ear.

Treatments. Because broad-spectrum insecticides may cause flare ups of other pests (for example, aphids or spider mites), only spray if thresholds are met. Pollen-shed is a time when there are large numbers of beneficials in the corn field doing important pest control work (Fig. 5), and foliar sprays may decrease their numbers.

lady beetle larva on corn leaf
Figure 5. Lady beetle larva eating corn pollen. Image: M. Cramer, University of Maryland

For Japanese beetles, consider a perimeter spray if most of the damage is on field edges (where they tend to feed more heavily). Japanese beetles are difficult to control, but pyrethroids should provide some control (e.g., Baythroid®, Brigade®, Warrior II®, Hero®, etc.). Good adult corn rootworm control has been found for indoxacarb products (e.g., Steward®), pyrethroids (e.g., Warrior II®, Brigade, etc.), and neonicotinoid pyrethroid mixes (e.g., Endigo®)6,7. When using insecticides, always consult and follow the label.

If silk clipping by Japanese beetles is a consistent problem, consider cultural controls like avoiding ryegrass and clover cover crops. Because female beetles lay eggs more easily into soft ground, it is also possible to reduce egg laying in nearby fields by pausing irrigation during the peak of Japanese beetle activity4.

Additional Resources:

  1. Nielson, R. L. Silk development and emergence in corn. (2020). https://www.agry.purdue.edu/ext/corn/news/timeless/silks.html
  2. Steckel, S., Stewart, S. D. & Tindall, K. V. Effects of japanese beetle (Coleoptera: Scarabaeidae) and silk clipping in field corn. J. Econ. Entomol. 106, 2048–2054 (2013). https://academic.oup.com/jee/article/106/5/2048/878220
  3. Dean Culy, M., Richard Edwards, C. & Ronald Cornelius, J. Effect of Silk Feeding by Western Corn Rootworm (Coleoptera: Chrysomelidae) on Yield and Quality of Inbred Corn in Seed Corn Production Fields. J. Econ. Entomol. 85, 2440–2446 (1992). https://academic.oup.com/jee/article-abstract/85/6/2440/847063?redirectedFrom=PDF
  4. Shanovich, H. N., Dean, A. N., Koch, R. L. & Hodgson, E. W. Biology and Management of Japanese Beetle (Coleoptera: Scarabaeidae) in Corn and Soybean. J. Integr. Pest Manag. 10, (2019). https://academic.oup.com/jipm/article/10/1/9/5454734
  5. Townsend, L. H. & Bitzer, M. J. Silk Clipping Insects on Corn. (1982). https://uknowledge.uky.edu/cgi/viewcontent.cgi?article=1053&context=anr_reports
  6. DeVries, T. A. & Wright, R. J. Evaluation of Foliar Applied Insecticides for Control of Adult Corn Rootworm in Corn, 2015: Table 1. Arthropod Manag. Tests 41, tsw080 (2016). https://academic.oup.com/amt/article/41/1/tsw080/2658080
  7. DeVries, T. A. & Wright, R. J. Evaluation of Foliar-Applied Insecticides for Control of Adult Corn Rootworm in Corn, 2015C: Table 1. Arthropod Manag. Tests 41, tsw096 (2016). https://academic.oup.com/amt/article/41/1/tsw096/2658095