Kelly Nichols, Agriculture Agent Associate University of Maryland Extension, Frederick County
Warmer temperatures and higher humidity are slowly making their appearance. Unfortunately, this means mosquitoes will soon make their appearance as well. Mosquitoes not only are pesky as they fly around you, but are a health risk for humans and livestock, as they carry diseases such as West Nile Virus and Zika Virus. Female mosquitoes need stagnant, nutrient-rich water in order to lay their eggs. After the mosquito eggs hatch, the larvae and pupae will live in the water before becoming an adult. The easiest solution to get rid of mosquitoes is to remove places where this water can accumulate.
Items such as water troughs, buckets, wheelbarrows, and bird baths should be stored inside or upside down when not in use. If stagnant water does accumulate while these items are in use, dump the water and replace it regularly. Loader buckets should be tilted downwards when stored to prevent water accumulation. Get rid of unused tires, and do not pile tires outside. If tires are outside, including those on top of bunk silos, cut them in half to reduce water accumulation. Tarps that cover bales or equipment should be placed so that water can drain. Gutters should be cleaned regularly.
For water sources that can’t be removed, there are insecticides and products that create a film on top of the water. Be sure to read the label before use. Note that the pupae do not actually eat during this stage, and therefore cannot ingest an insecticide, so it is important to use the right product for the correct stage. Creating a film on top of the water’s surface prevents the pupae from being able to access air to survive. Crusts on manure pits can act as a film; however, keep in mind that if using an insecticide, the crust will prevent it from reaching the larvae. Reduce weeds around the pit to deter mosquito habitat. If ponding is occurring in fields and around the barnyard, determine the cause and take the necessary actions. These actions may include alleviating compaction, fixing gutters, or fixing drainage pipes.
Emily Zobel, Agriculture Agent Associate University of Maryland Extension, Dorchester County
Overwintering bean leaf beetles are emerging and starting to feed. Soybean seedlings can recover, with no yield loss, from 40% defoliation. Many small caterpillars, such as the green clover worms will also defoliate plants. However, once soybean plants start to bloom, you want to control defoliating insects when you have greater than 15% defoliation.
Check for cutworm and armyworms leaf feeding on young corn plants. The threshold for cutworms is when 10% of the field has feeding damage at 1-2 leaf, and 5% damage at 3-4 leaf or 4 larvae found per 100 ft. For armyworms, the treatment threshold is when 25% of the plants are infested and larvae are under a 0.75 inch long. Armyworms that are 1.25 inches are late instars and have likely completed their feeding.
No-till fields of both corn and soybean are at an increased risk of slug damage. Slugs feed at night, so you will likely not find them during daytime scouting. Their feeding damage will be found on the lower leaves of plants. The leaf will have narrow, irregular, linear tracks or scars of various lengths that may be eaten partly or entirely through the leaf. Peter Coffey wrote a great article about slug management, which can be found here (https://blog.umd.edu/agronomynews/2018/05/03/what-should-i-do-about-slugs/) .
As wheat gets harvested during the month, stink bugs may move into nearby cornfields. Their feeding could affect the developing ear and kernels. Populations will be highest around the edge of the field, and full-field control may not be needed. Field corn treatment threshold are when 25% of plants are infested with stink bugs before pollination, and 50% of plants are infested with stink bugs are after pollination up to early dough stage. Counts should be done on 10 plants in 10 different locations in the field. Do not count beneficial stinkbugs, such as the spined soldier bug.
Alan Leslie1, Agriculture Agent; Kelly Hamby2, Extension Specialist; and Galen Dively, Professor Emeritus2 1University of Maryland Extension, Charles County 2University of Maryland, Department of Entomology
This time of year, anyone growing small grains will be planning to apply fungicides to manage Fusarium head blight, and many will consider tank-mixing an insecticide to control any insect pest problems at the same time. These tank mixes are an appealing option to reduce the time, fuel, and damage to the crop from having to make a second pass over the field later on in the season. In addition, with many synthetic pyrethroids now available as cheaper generic versions, the costs associated with adding an insecticide to the tank may seem like cheap insurance against possible pest outbreaks. However, to ensure that this added investment gives you a return with increased yields, you should still follow an integrated pest management approach and base the decision to add an insecticide on scouting and documentation of an existing pest problem. Below, we outline several possible insect pests that could be controlled with an insecticide applied with fungicides over small grains, and summarize situations where that application may be warranted, and when it may not.
Aphids. Aphid populations need to be controlled in the fall to reduce Barley Yellow Dwarf Virus incidence in small grains. Spring insecticide applications will not reduce incidence of the disease. Only a few aphid species tend to feed on grain heads, and can reduce yield from head emergence through milk stage (Fig. 1). After the soft dough stage, no economic losses occur. Aphid populations are generally kept in check by insect predators and parasitoids, and thresholds for chemical control of aphids in the spring require at least 25 aphids per grain head (with 90% of heads infested) or 50 per head (50% heads infested) and low numbers of natural enemies. Applying a broad spectrum insecticide when aphid pressure is not above threshold tends to kill off beneficial predatory and parasitic species, which can allow aphid populations to flare up, as they are no longer being suppressed by their natural enemies.
Figure 1. Aphids feeding on wheat head.
True armyworm and grass sawfly. Both true armyworm (Fig. 2) and grass sawfly (Fig. 3) are sporadic pests of small grains and their pest pressure and feeding damage can vary widely from year to year. Automatically applying an insecticide to target these pests is not likely to be a cost-effective strategy since they are not pests that reliably cause economic injury. When these pests are present in high numbers, they are capable of causing significant yield loss through their behavior of clipping grain heads. Scouting should be done to check for the presence of these two pests and insecticide treatment is only needed if they exceed threshold values of one larva per linear foot for armyworm and 0.4 larvae per linear foot for grass sawflies.
Hessian fly. Cultural methods are the best way to control Hessian fly in small grain, such as planting after the fly-free date, selecting resistant varieties, and using crop rotation to disrupt their population growth. Spring feeding by the fly larvae can cause stems to break, reducing yields. There are no effective rescue treatments for Hessian fly; insecticides targeting fly larvae are ineffective since they are well protected from sprays by feeding inside of the leaf sheath (Fig. 4). If this year’s crop is damaged, it is imperative that fly-resistant varieties are planted after the fly-free date next year.
Cereal leaf beetle. This species is widespread in Maryland and is typically present in small grains, though it only occasionally reaches levels that injure crops. Cereal leaf beetle larvae chew the upper surfaces of leaves, leaving them skeletonized (Fig. 5). Larvae can cause yield loss if the flag leaf is severely skeletonized before grain-fill is completed. Insecticides with good residual activity tank mixed and applied with fungicides can potentially control populations of cereal leaf beetles, protect the flag leaf, and improve the yield of the crop if beetle pressure is high. However, predicting whether populations will reach damaging levels is not straightforward, and scouting should be used to guide spray decisions. If a field has 25 or more larvae plus eggs per 100 tillers, and there are more larvae than eggs, then chemical control is needed. In Maryland, a parasitoid wasp species (Anaphes flavipes) may parasitize 70-98% of cereal leaf beetle eggs, so if a field is dominated by eggs with few larvae, insecticide may not be needed. Additionally, feeding by cereal leaf beetle will not cause economic damage after the hard dough stage. So far, we have received no reports of economic levels of cereal leaf beetle in the region.
Figure 5. Cereal leaf beetle larva and feeding damage.
In conclusion, tank mixing an insecticide with your fungicide application can pay off if you have economically damaging levels of an insect pest, but applying any insecticide without a pest problem will not pay off. If populations are present, seem to be increasing, and you will not be harvesting soon, you could gamble. The risks of that gamble include losing money on an unnecessary input cost, secondary pest outbreaks if natural enemy populations are wiped out, or the target pest outbreaks anyway because the application was poorly timed. Scouting fields regularly to document pest pressure and using IPM thresholds as a guide for using chemical controls is the best way to hedge your bets when deciding whether to add an insecticide to the tank this spring.
For more information on tank-mixing insecticides with small grain fungicide applications, check out current research updates from Dr. Dominic Reisig at North Carolina State University: https://smallgrains.ces.ncsu.edu/2019/03/aphids-in-wheat/
Alan Leslie Agriculture Extension Agent, Charles County
After a relatively mild winter, we are getting reports of high numbers of alfalfa weevils causing damage to alfalfa fields in Southern MD. Eggs that were laid by alfalfa weevil adults last fall are all hatching now, and early spring is when the larvae can cause the most damage to alfalfa stands, reducing the yield and quality of the first cutting and potentially setting the entire stand back for the rest of the year. Now is the time to be scouting for larvae and to consider chemical treatment to prevent economic yield loss. Alfalfa weevil larvae look very similar to caterpillars, with a dark head and a green body with a white stripe running down the middle. Early signs of injury from alfalfa weevil larvae appear as pinholes in leaves, but extensive feeding will skeletonize leaves, leaving plants with a distinct gray color. Sweep nets do not do a very good job of catching small larvae, so the best way to scout your fields is to cut stems and beat them on the inside of a bucket to knock the larvae loose. To effectively sample a field, you should collect at least 30 stems from across the field, and beat them vigorously inside the bucket. Make sure to keep track of the exact number of stems you sample, so you can calculate the average number of larvae per stem. Thresholds for control depend on the average height of the stand at the time you sample, with the threshold increasing in taller plants (Table 1).
Table 1.Threshold numbers of larvae per plant for different average stand heights that would warrant chemical control
Stand height (inches)
Larvae per plant
0-11
0.7
12
1.0
13-15
1.5
16
2.0*
17-18
2.5*
*At these stand heights, prompt or early harvest can also control the larval infestation
We have also gotten reports of less than adequate control of alfalfa weevil populations using synthetic pyrethroids (group 3A; beta-cyfluthrin, zeta-cypermethrin, permethrin, lambda-cyhalothrin, cyfluthrin). Because synthetic pyrethroids have historically been such a cheap and reliable chemical class, they have been widely used on many pests, and there are many examples of insect species becoming resistant to this class of insecticide. Currently we do not have good data on the extent to which local populations of alfalfa weevil are becoming resistant to pyrethroids, but it is always a good idea to rotate modes of action of insecticides sprayed over your fields to help prevent resistant populations from developing. Other chemical classes that give effective control of alfalfa weevil include carbamates (group 1A; methomyl, carbaryl) organophosphates (group 1B; phosmet, malathion, chlorpyrifos), and oxadiazines (group 22A; indoxacarb). If you have any remaining chlorpyrifos in your inventory, this may be a good opportunity to use it up, since the state of Maryland will likely introduce legislation to ban its use this year or in the near future. Remember to always read and follow the label whenever making any insecticide applications; the label is the law!
Darsy Smith, Graduate Student & Dr. William Lamp, Professor University of Maryland, Department of Entomology
Figure 1. Yellow appearance of the alfalfa field that lead to the discovery of the cowpea aphid outbreak at BARC. Photo courtesy of Russell Griffith.
An unexpected outbreak of cowpea aphid, Aphid craccivora Koch, in Maryland was discovered last month by Terry Patton, who was contacted by Russell Griffith, tractor operator leader at Beltsville Agricultural Research Center (BARC), because of the yellow appearance of an alfalfa field (Figure 1) and the infestation of dark aphids (Figure 4). Since the 1990s, infestations of the cowpea aphid have been observed in Maryland alfalfa, but this is an unusually large outbreak. Stay alert to this emerging pest and learn how to identify it since it has a wide range of hosts and may damage crops.
Figure 2. Adult cowpea aphid. Note the cornicle (yellow arrow) is dark and long and the abdomen (red arrow) is distinctive dark and shiny. Photo courtesy of influentialpoints.comFigure 3. Adult and nymph cowpea aphids. Nymph color is opaque and varies (yellow arrow) from brown to gray while the adult (red arrow) has the distinctive dark, shiny abdomen. Photo courtesy of Andrew Jensen, https://aphidtrek.org/
Cowpea aphid identification and injury. Cowpea aphid is not generally an economic pest in alfalfa but learning how to identify the aphid and its injury can help you prevent losses. Cowpea aphid is easily differentiated from other aphids in alfalfa because its dark coloration, with the abdomen of the adults much darker and shinier than the rest of its body (Figure 2). In addition, the cornicle (or siphuncule) is dark and long (Figure 2). The nymph is less shiny (opaque) and varies from brown to gray (Figure 3). The legs and antennae of both adults and nymphs are pale with dark tips (this characteristic is more distinctive in adults).
The cowpea aphid is a sap-sucking feeder and damage caused in alfalfa by this pest results from the injection of a toxin into the phloem of the plant. With high population densities on plants, the aphid can cause stunting or plant death. In addition, it can cause yellowing in alfalfa leaves (Figure 1). Like other aphids, this insect produces honeydew that will benefit fungus growth and eventually cause sooty mold.
How to find them? Cowpea aphids are usually found in clusters on the alfalfa leaf and stems (Figure 4). It can also be found in vegetative growth and flower parts of a wide range of hosts. They are readily sampled with sweep nets.
Figure 4. Cowpea aphids on growing tip of alfalfa at BARC. Photo courtesy of Russell Griffith.
Host plants. Cowpea aphid is most commonly found in alfalfa, but may be found on other legumes, such as clovers. More uncommonly, the aphids occur on a variety of weeds and other plants in other plant families.
Management options. Unfortunately, there is not an economic threshold specified for this pest in Maryland alfalfa at this point. However, here are general guidelines for responding to the pest:
Conserve natural enemies. Natural enemies such as lady beetles, damsel bugs, and parasitoid wasps often locate, feed, and reproduce in conjunction with high densities of aphid in alfalfa. If you conserve natural enemies you might find aphids parasitized by parasitoid wasps (Figure 5). When scouting for aphids, watch for natural enemies to help control aphid populations. To help natural enemies stay in your alfalfa field you can use border-strip cutting while harvesting to provide refuge habitats. For more information of this practice, see “Harvest Scheduling and Harvest Impacts on IPM” at the end of this report.
Monitoring for decision-making. Early infestations in alfalfa can result from migration from southern areas. Pay attention to alfalfa fields in March and continue to monitor until fall. Since there are no thresholds developed for cowpea aphid, the thresholds for insecticide applications developed for the blue alfalfa aphid can be used: if alfalfa is 10 inches, then treat if there are 20 or more aphids per stem; if alfalfa is 20 inches tall, then treat if 50 or more aphids per stem.
Figure 5. Aphids parasitized or aphid mummies by a parasitoid wasp. Note the emergence hole (yellow arrows) of the parasitoid wasp in the mummy. Photo courtesy of Darsy Smith.
Potential reasons for the outbreak.
Researchers in the Lamp Lab, University of Maryland, have noted this pest in greenhouse settings but rarely observed them in alfalfa fields. Dr. Lamp suggests that the cowpea aphid may have migrated into Maryland because this species is more common in southern and western areas. Also, the mild winter may have allowed individuals that migrated last year to overwinter in Maryland. Additionally, lack of natural enemies in early spring can potentially lead to an outbreak. Conserving the natural enemies in alfalfa fields and neighboring areas can help decrease aphid abundance.
How can you help?
Records from your alfalfa fields and surrounding crops are valuable sources of information. The information is helpful to not just explain an outbreak but also to provide useful guidelines for farmers to manage the crop and avoid a future outbreak. Practical information that you can provide include any of the following:
Date of first time you have observed the pest
Date of outbreak
Plant height and phenology stage: when you observed the pest for the first time and during outbreak
Presence of natural enemies
Pesticide use and efficacy of application
Alfalfa cultivars/varieties planted during outbreak and previous year
Pictures of damage and estimate of loss
If you find cowpea aphid in your alfalfa field, please contact the nearest county extension office.
Kelly Hamby, Terry Patton, and Galen Dively Department of Entomology, University of Maryland College Park
Summary. Weather stations in Baltimore, MD recorded the 3rd warmest winter on record in 81 years from Dec 2019 to February 2020, with 10% of our 30 year average snowfall (NOAA National Climate Report). Insects that overwinter as immatures or adults in above-ground protected areas are typically favored by mild winters, especially species that are not cold-hardy because much of the population would typically die during the winter. However, the lack of snowfall can also reduce overwintering survival because snow can insulate against freezing temperatures. Mild winter conditions favor green bug aphids and winter grain mite outbreaks in small grains and orchardgrass, and these pest populations can build rapidly. Fortunately, mild winters also favor many beneficial natural enemies. Greenbug aphid outbreaks have been observed in central Maryland orchardgrass (see Figure 1), and greenbugs have also been observed in Delaware. Overall, aphid populations have been spotty in Delaware and promising natural enemy activity has been observed (UD Weekly Crop Update, March 20). However, close surveillance is necessary when greenbug is the predominate species because greenbug injects toxic saliva during feeding and can be very destructive. It is important to carefully scout your fields for aphids multiple times to determine whether populations are building or crashing on your farm. Management interventions may be necessary to prevent economic losses. Winter grain mites may also be a problem this year and scouting close to the soil surface is necessary to catch this issue in a timely manner.
Figure 1. Heavy aphid populations have been observed in orchardgrass in central Maryland.Figure 3. Aphid damage to orchardgrass in central Maryland.
Cereal Aphids and Greenbugs. Multiple species of aphid occur in Maryland small grains and orchardgrass (see Figure 2) and aphids can vector barley yellow dwarf virus. Bird-cherry oat aphids vector the most severe strain and may need to be managed in the fall to prevent damage from barley yellow dwarf, especially in intensive management wheat. Although the direct damage from aphid feeding is generally similar across species, it is especially important to record species if greenbugs are present. Greenbug saliva contains enzymes that break down cell walls, so their feeding is most damaging. They initially cause spotting on the leaf followed by discoloration and eventual leaf and root death if feeding continues. Grain cultivars vary in their tolerance for greenbug damage. One of the first noticeable symptoms of aphid outbreaks are circular yellow to brown spots with dead plants in the center (see Figure 3); however, aphid damage may be confused with moisture stress and/or nitrogen deficiency so make sure to scout for aphids especially in areas that are showing stress symptoms. Scout a minimum of 1 linear row foot in 10 sites, the more row feet and locations the better, and estimate the number of aphids per foot of row. The rule of thumb treatment threshold for small grains is to treat if counts exceed 150 per linear foot throughout most of the field, with few natural enemies detected (e.g., mummy aphids, lady beetles, fungal infections). One natural enemy to every 50 to 100 aphids can be enough to control the population. This threshold may be lower if greenbugs are the predominant aphid and greenbug populations should be carefully monitored. Foliar insecticides including pyrethroids (Group 3A), neonicotinoids (Group 4A), and organophosphates (Group 1B) can be used to control aphids.
Figure 2. Common cereal aphids. Notice color and length of antennae and cornicles (tail pipes). Greenbugs are light green with a dark green stripe, with black tips of the legs, cornicles, and antennae. Photos: Various Extension websites.
Winter Grain Mite. Winter grain mites are a cool season pest of small grains and orchardgrass that cause a silvery leaf discoloration from feeding damage that punctures individual plant cells. Feeding can also stunt plants. Winter mites have a dark brown to black body with bright reddish-orange legs (see Figure 4). Somewhat uniquely, their anal opening is on the upper surface and can appear as a tan to orange spot that is more visible under magnification. Two generations of winter grain mite occur per year and are active from the fall to early summer. They oversummer in the egg stage, with the first generation hatching around October and adult populations peaking in December or January. The second generation peaks from March to April and produces the oversummering eggs. Because spring eggs result in fall populations, rotating the crop away from grasses and managing wild grasses around field edges can be helpful to reduce populations. Adult activity occurs when temperatures are between 40 and 75°F, and they prefer cool, cloudy calm weather. Therefore, winter grain mites are easier to see during these conditions, and more likely to be higher on the plant during the early morning or late evening. If you are scouting on a hot, dry day or in the middle of the day, you should check under residue where the soil is moist, and may need to dig 4 or 5 inches into the soil to find the mites. Winter grain mite does not typically cause economic damage, and no thresholds have been developed. If large portions of a field show symptoms and mites are present, treatment may be warranted. No products are specifically labeled for winter grain mite; however, products labeled for brown mite such as dimethoate (Group 1B, in wheat only) are likely to be effective. Warrior II (pyrethroid, Group 3A) may also provide suppression.
Maria Cramer, Edwin Afful, Galen Dively, and Kelly Hamby Department of Entomology, University of Maryland
Slug feeding damage: characteristic long, thin holes made by a rasping mouthpart.
Background: Multiple insecticide options are available for early-season corn pest management, including neonicotinoid seed treatments (NSTs) and in-furrow pyrethroids such as Capture LFR®. In addition, many Bt corn hybrids provide protection against seedling foliar pests such as cutworm and armyworm. Given that almost all corn seed is treated with neonicotinoid seed treatments (NSTs), Capture LFR® may not provide any additional protection.
Methods: In this study we compared four treatments: fungicide seed treatments alone; Capture LFR® (active ingredient: bifenthrin) applied in the planting furrow with the fungicide seed treatment; Cruiser Maxx® 250, an NST (active ingredient: thiamethoxam), which includes a fungicide; and Capture LFR® + Cruiser Maxx® 250 together. We evaluated the amount of soil and foliar pest damage after emergence. Yield was measured at harvest.
Preliminary results: Our results suggest that when wireworm pressure is high, Capture LFR® and Cruiser Maxx® 250 protect against damage and significantly increase yields. Neither treatment is superior, so we recommend using only one, and only in fields where pest pressure is known to be high. As most corn seed already contains NSTs, use of Capture LFR® at planting is unlikely to be warranted.
Sampling for soil and foliar pests
Background: Capture LFR®, an in-furrow pyrethroid product, is marketed for control of early-season corn pests, including soil pests such as white grub and wireworm and above-ground pests such as cutworm and armyworm. However, the insect pest management systems already adopted in corn may provide sufficient protection. Most corn seeds are treated with NSTs, which provide seedlings with systemic protection from many soil and above-ground pests. Additionally, most Bt corn hybrids express proteins with efficacy against cutworm and armyworm in the seedling stage, although they do not affect soil pests. Unlike NSTs and Bt traits, pyrethroids are not systemic and do not provide protection beyond the soil area to which they are applied.
While in-furrow applications of bifenthrin (the active ingredient in Capture LFR®) can effectively reduce wireworm damage in potatoes1 and provides white grub control in field corn2,3, it does not consistently increase yield in corn3 or soybeans4. Yield benefits are likely to be seen only where there is known soil pest pressure. Meanwhile, preventative applications of pyrethroids have been linked to declines in natural enemies 5,6, including carabid beetles, which are important predators of slugs.
Objectives: Our objectives were to determine whether in-furrow applications of Capture LFR® (bifenthrin) provided 1) protection against soil pests, 2) protection against seedling pests, and 3) yield benefits compared with fungicide alone, Cruiser Maxx® 250, or combined with Cruiser Maxx® 250.
Methods: This study was conducted in 2018 and 2019 at the University of Maryland research farm in Beltsville, MD. We planted 4 replicate plots of a standard Bt field corn hybrid, TA 758-22DP (VT Double Pro insect control) in 2018 and LC1488 VT2P (SmartStax RIB complete insect control) in 2019 at 29,999 seeds per acre. Plots were planted late in 2018 (June 18) but on time in 2019 (May 20). Standard agronomic growing practices for the region were used. We compared the following four treatments, applied at planting:
No in-furrow application
In-furrow Capture LFR®
Applied at 13.6 fl oz/ac
Fungicide seed treatment
Fungicide (F) seed treatment alone
2018: Maxim Quattro®
2019: Vibrance Cinco®
Fungicide +
Capture LFR® (F + Cap)
Cruiser Maxx® 250
Cruiser Maxx® 250
(Cru)
Cruiser Maxx® 250 + Capture LFR® (Cru +Cap)
We sampled plants 24 days after planting in 2018, and 18 days after planting in 2019. In 2018, we recorded the number of stunted plants (indicating potential soil pest damage), and in 2019, we dug up stunted plants and recorded those for which soil pest damage could be confirmed. In both years, we assessed rates of above-ground feeding by pests such as cutworm and armyworm.
Wireworm (left) and characteristic above-ground symptoms of wireworm feeding (right). Note wilted center leaf.Results: Soil Pests. In 2018 there was no difference in the percent stunted plants between treatments (Figure 1), with less than 5% stunting in all treatments. This low level of pest damage may have been due to the late planting date, which could have avoided peak soil pest pressure. In 2019, all of the insecticide treatments had significantly lower soil pest damage than the fungicide control (Figure 1). Combining Capture LFR® with Cruiser Maxx® 250 was not more effective than Cruiser Maxx® 250 alone, but was more effective than Capture LFR® alone, suggesting that treatments involving Cruiser Maxx® 250 are somewhat more effective against the soil pests at this farm. In both years, plots were located in a field with a history of wireworms; however, damage was only observed in 2019. In a field without pest pressure, such as we saw in 2018, these treatments did not improve plant stand.
Foliar pests. In both 2018 and 2019, rates of foliar damage were extremely low (below 5% of plants) in all treatments and there were no differences between treatments.
Yield. In 2018, there were no yield differences between the treatments (Figure 2). Overall, we had low yields in 2018, likely a result of the late planting date. In 2019, all of the insecticide treatments had significantly higher yields than the fungicide control, with no differences between any of the insecticide treatments (Figure 2). Combining Capture LFR® with Cruiser Maxx® 250 did not increase yield.
Figure 1. 2018 and 2019 soil pest pressure, Beltsville, MD. Mean percent plants damaged for four treatments: F=Fungicide, F+Cap= Fungicide + Capture LFR®, Cru=Cruiser Maxx® 250, Cru+Cap= Cruiser Maxx® 250 + Capture LFR®. In 2018, treatments did not impact stunted plants (N.S.) In 2019, all insecticide treatments significantly reduced soil pest damage (columns with different letters have significantly different mean damage).Figure 2. 2018 and 2019 yields, Beltsville, MD. Mean yield for four treatments: F=Fungicide, F+Cap= Fungicide + Capture LFR®, Cru=Cruiser Maxx® 250, Cru+Cap= Cruiser Maxx® 250 + Capture LFR®. Yields were not significantly different in 2018 (N.S). In 2019, all insecticide treatments had significantly higher yield than the fungicide only treatment (columns with different letters have significantly different mean yield).
Conclusions: In 2018 and 2019 we did not see sufficient foliar pest pressure to justify an insecticide application. This may be due to effective control by Bt proteins in the corn hybrids and/or low foliar pest pressure.
In a field with established wireworm pressure, all three insecticide treatments reduced soil pest damage and improved yield relative to a fungicide only control in the 2019 field season. While there were differences in pest damage levels between the different insecticide treatments, no one treatment provided superior yield benefits. Because nearly all corn seed is treated with NSTs like Cruiser Maxx® 250, additional applications of Capture LFR® may not be necessary. Preventative applications increase costs and present risks to beneficial insects without providing yield benefits. Additionally, soil pest pressure tends to be low throughout Maryland. We sampled untreated corn at five locations across Maryland in 2019 and found on average less than 3% soil pest damage. Unless a field has a known history of wireworms or white grubs, we do not recommend using at-planting insecticides.
Acknowledgements and Funding. This project was funded in both years by the Maryland Grain Producers Utilization Board. We appreciate the help provided by Rachel Sanford, Madison Tewey, Eric Crandell, Gabriel Aborisade, and Kevin Conover.
Sources
Langdon, K. W., Colee, J. & Abney, M. R. Observing the effect of soil-applied insecticides on wireworm (coleoptera: Elateridae) behavior and mortality using radiographic imaging. J. Econ. Entomol.111, 1724–1731 (2018).
Afful, E., Illahi, N. & Hamby, K. Agronomy News. 10, 2–4 (2019).
Reisig, D. & Goldsworthy, E. Efficacy of Insecticidal Seed Treatments and Bifenthrin In-Furrow for Annual White Grub, 2016. Arthropod Manag. Tests43, 1–2 (2017).
Koch, R. L., Rich, W. A., Potter, B. D. & Hammond, R. B. Effects on soybean of prophylactic in-furrow application of insecticide and fertilizer in Minnesota and Ohio. Plant Heal. Prog.17, 59–63 (2016).
Douglas, M. R. & Tooker, J. F. Meta-analysis reveals that seed-applied neonicotinoids and pyrethroids have similar negative effects on abundance of arthropod natural enemies. PeerJ 1–26 (2016). doi:10.7717/peerj.2776
Funayama, K. Influence of pest control pressure on occurrence of ground beetles (Coleoptera: Carabidae) in apple orchards. Appl. Entomol. Zool.46, 103–110 (2011).
Adult spotted lanternfly. Image: Lawrence Barringer, Pennsylvania Department of Agriculture, Bugwood.org
Reposted from Maryland Department of Agriculture press release
The Maryland Department of Agriculture today issued a spotted lanternfly quarantine for all of Cecil and Harford Counties. This quarantine is effective immediately and will restrict the movement of regulated articles within the quarantine zone that contain the spotted lanternfly in any of its life stages, including egg masses, nymphs, and adults.
Examples of regulated articles include landscaping, remodeling, or construction waste; packing materials like wood boxes or crates; plants and plant parts; vehicles; and other outdoor items.
Following the department’s 2019 survey season, these two counties were found to have established populations of spotted lanternfly. The quarantine has been issued in an effort to control the spread of this invasive insect to other parts of the state. A map of the quarantine zone can be viewed here.Businesses, municipalities, and government agencies that require the movement of any regulated item within or from the quarantine zone must have a permit. A permit can be obtained by taking a free online training course through PennState Extension. Upon completion of the course and an online exam, individuals will receive a permit.
Managers, supervisors, or employees of a business or organization operating in the quarantine zone must receive the approved training and pass the exam by at least 70% to demonstrate a working knowledge and understanding of the pest and quarantine requirements. Training of other employees, inspection of vehicles and products, and removal of living stages of spotted lanternfly must also be completed.
All spotted lanternfly permits for Virginia, Pennsylvania, New Jersey, and Delaware are transferable and valid throughout the region — meaning a permit from any of these states can be used in Maryland. Maryland is currently in the process of developing its own training and permitting system for spotted lanternfly.
Those living within the quarantine zone are encouraged to be vigilant in containing the spread of spotted lanternfly. The department has created a residential compliance checklist that is available for download on its website that educates residents on the lifecycle of the spotted lanternfly, and areas to inspect around the home.
The spotted lanternfly poses a major threat to the region’s agricultural industries as it feeds on over 70 different types of plants and crops, including grapes, hops, apples, peaches, oak, pine, and many others. Originally from Asia, the spotted lanternfly is nonnative to the U.S., and was first detected in Berks County, Pennsylvania in the fall of 2014. As a known hitchhiker, the spotted lanternfly has spread to 14 counties within Pennsylvania, and also has confirmed populations in Delaware, Virginia, and New Jersey.
This fall, the department’s Plant Protection and Weed Management Program partnered with the U.S. Department of Agriculture (USDA) to treat Ailanthus altissima for spotted lanternfly at multiple sites in the upper northeast corner of Cecil County, and along the northern border of Harford County. In total, 2,698 trees have been treated (2,403 trees in Cecil County and 295 trees in Harford County). The program continues to work with USDA Animal and Plant Health Inspection Service Plant Protection and Quarantine program, University of Maryland Extension and others to monitor the insect in Maryland.
If you suspect you have found a spotted lanternfly, snap a picture of it, collect it, put it in a plastic bag, freeze it, and report it to the Maryland Department of Agriculture at DontBug.MD@maryland.gov. Dead samples from any life stage can be sent to the Maryland Department of Agriculture Plant Protection and Weed Management Program at 50 Harry S. Truman Parkway, Annapolis, MD 21401.
More information about the spotted lanternfly can be found on the department’s website. For questions related to the quarantine, permitting, or treatment, please contact that Plant Protection and Weed Management Program at 410-841-5920.
Maria Cramer, Edwin Afful, Galen Dively, and Kelly Hamby Department of Entomology, University of Maryland
Overview
Background: Due to their low cost, pyrethroid insecticides are often applied when other chemical applications are made. For example, they may be included in tank mixes with herbicides in early whorl corn and with fungicides during tasseling. These pyrethroid sprays often target stink bugs; however, the timing of these treatments is not ideal for stink bug management. Pyrethoid insecticides may harm beneficial insects that help keep pest populations in check and repeated use of pyrethroids can contribute to insecticide resistance.
Methods: In this study, we examined the effect of Bifenture EC® (pyrethroid active ingredient: bifenthrin) applied with herbicides in V6 corn and with fungicides in tasseling corn. We evaluated impacts on pests and beneficials at both application timings. Yield was measured at harvest.
Preliminary Results:At both application timings, Bifenture EC® did not improve insect pest management because pests were not present at economic levels. We did not find evidence for flare-ups of aphids or spider mites, but a rainy late summer made it unlikely that we would see many of these pests. There were no yield differences between the treatments.
Background
As a result of the low cost of pyrethroid insecticides, preventative applications are common, especially in tank mixes with other routine chemical inputs, such as herbicides and fungicides. However, lower grain prices and low insect pest pressure make it less likely that pyrethroid applications will provide economic returns. Bt hybrids1 and neonicotinoid seed treatments control many of the pests targeted by pyrethroid insecticides. Because they have broad spectrum activity, pyrethroids can negatively impact natural enemies2 which can result in flare-ups of secondary pests3. Tank mix timings may be less effective than applying when insect populations reach threshold. For example, when pyrethroids are combined with herbicide applications, they are too late to control early-season stink bugs and other seedling pests. When pyrethroids are combined with fungicide sprays at tasseling, few insect pests are present at damaging levels. Stink bugs may feed on the developing ear at this time, causing deformed “cowhorned” ears; however, this is rarely a problem in Maryland and stink bug damage is generally not economic throughout a field because feeding is primarily concentrated at the field edge4. Insecticide applications at tasseling have a high potential to affect beneficial insects, especially pollinators and natural enemies that are attracted to corn pollen.
Objectives: Our objectives were to determine the effect of pyrethroids applied preventatively in tank-mixes on corn pests, beneficials, and yield.
Methods: This study was conducted in 2018 and 2019 at the University of Maryland research farm in Beltsville, MD. For each application timing, we planted four replicate plots of a standard Bt field corn hybrid, DeKalb 55-84 RIB (SmartStax RIB complete Bt insect control in addition to fungicide and insecticide seed treatments) at 29,999 seeds per acre. Standard agronomic practices for the region were used.
Herbicide (same as above) + Insecticide (Bifenture EC® 6.4 oz/acre)
Treatments were applied at V6/V7. We visually surveyed corn plants for pest and beneficial insects before and after application. We also placed sentinel European corn borer (ECB) egg masses in the field to assess predation rates before and after treatment.
The fungicide timing compared two treatments:
Fungicide alone (Trivapro® 13.7 oz/acre)
Fungicide (same as above) + Insecticide (Bifenture EC® 6.4 oz/acre)
Treatments were applied at green silk. We inspected the ear zone and silks for pests and beneficial insects before application. After application, we recorded the number of ears with pest damage and the kernel area damaged. We also counted stink bug adults and cowhorned ears. Six weeks after application, we visually assessed plants for spider mite and aphid colonies.
Sampling for pests and beneficials (left) and; sentinel European corn borer egg mass (right).
Results
In the herbicide-timing study in 2019 we observed no effect on beneficial insects from the treatments (Figure 1). The most abundant beneficial species were minute pirate bugs and pink spotted lady beetles, which are very mobile and may have recolonized treated plots after treatment. Similarly, treatments did not affect predation on the sentinel egg masses, suggesting that the pyrethroid application may not have affected predators’ ability to locate and consume eggs. Across the treatments, 30-50% of egg masses were consumed by predators.
Minute pirate bug on European corn borer egg mass.
The treatments did not impact the number of beneficials at the herbicide timing (N.S.). The pyrethroid insecticide significantly reduced the number of plant hoppers and plant bugs from less than 4 per plant on average to less than 2 per plant (significantly different p<0.05, *), though these insects are not economic pests at this stage. There were never more than 2 stink bugs per 90 plants, well below the treatment threshold of 13 per 100 plants4.
In the fungicide-timing study in 2019, beneficials, especially minute pirate bugs, were abundant at the time of application (3 in every 10 plants), while stink bugs, the presumed target pest, were very rare (1 stink bug in every 68 plants). In 2018, stink bugs were similarly scarce. Overall pest abundance was low (1 in every 35 plants). After application, there was no difference in the incidence or amount of the corn ear damaged by worms, stink bugs, or sap beetles between treatments. Average stink bug and earworm incidence was roughly 1 in 10 ears, while sap beetle was even less frequent. Cowhorned ears and adult stink bugs were almost non-existent in both treatments.
Six weeks after application we found no differences in aphid or spider mite populations between the treatments, suggesting that pyrethroid applications at tasseling did not cause secondary pest outbreaks. We sampled after a period of dry weather; however, the late summer was rainy at Beltsville, which likely suppressed spider mite and aphid populations. Under drought-stress, reductions in the natural enemy population from pyrethroid use might contribute to flare-ups of aphids and spider mites.
Figure 1. Herbicide timing. July 3, 2019, Beltsville MD. Mean number of insects per 10 plants in V7 corn after treatment. N.S.=not significant. H=herbicide; P=pyrethroid.
Yield
For the herbicide timing and fungicide-timing (Figure 2) studies, treatments did not affect yields in either 2018 or 2019.
Conclusions
Figure 2. Herbicide timing (left) and fungicide timing (right), 2018 and 2019, Beltsville MD. Mean yield per acre under two treatments. Yields were not significantly different by treatment in either study. For the fungicide-timing study, 2019 yields were significantly higher than in 2018. N.S.=Not Significant. H=Herbicide; F=Fungicide; P=Pyrethroid.
Results from the 2018 and 2019 studies suggest that pyrethroid applications do not provide yield benefits in corn when tank-mixed with herbicides or fungicides, likely due to the lack of insect pest pressure at these spray timings. Beneficial insects were abundant in the crop at each of these timings and did not appear to be affected by the pyrethroids in the herbicide plots. Repeated preventative use of pyrethroids in the same field could potentially hinder the natural biocontrol of corn pests.
Lady beetle larva (a predatory insect) in silks.
Sources
1 DiFonzo, C. 2017. Handy Bt Trait Table for U.S. Corn Production, http://msuent.com/assets/pdf/BtTraitTable15March2017.pdf
2Croft, B.A., M.E. Whalon. 1982. Selective toxicity of pyrethroid insecticides to arthropod natural enemies and pests of agricultural crops. Entomophaga. 27(1): 3-21.
3Reisig, D.C., J.S. Bacheler, D.A. Herbert, T. Kuhar, S. Malone, C. Philips, R. Weisz. 2012.Efficacy and value of prophylactic vs. integrated pest management approaches for management of cereal leaf beetle (Coleoptera: Chrysomelidae) in wheat and ramifications for adoption by growers. J. Econ. Entomol. 105(5): 1612-1619
4Reisig, D.C. 2018. New stink bug thresholds in corn, https://entomology.ces.ncsu.edu/2018/04/new-stink-bug-thresholds-in-corn/
Morgan N. Thompson & William O. Lamp University of Maryland, Department of Entomology
Nitrogen is a critical nutrient for forage crop growth and quality. Typically, farmers need to apply additional nitrogen fertilizers to meet the nitrogen demand of crops. Nitrogen-fixing crops, however, do not require nitrogen fertilizer inputs, providing their own nitrogen supply through symbiotic interactions with soil microbes (rhizobia). Rhizobia induce the formation of root nodules in nitrogen-fixing crops, predominantly legumes, and extract inert nitrogen gas from the atmosphere to produce ammonium. In exchange for ammonium, legumes provide the rhizobia carbohydrates to fuel the microbe’s metabolism. Alfalfa is a leguminous forage crop that relies on symbiotic interactions with rhizobia to obtain nitrogen. As a perennial crop, alfalfa stands can last from 3-7 years and typically require no nitrogen fertilizer inputs, making alfalfa a sustainable and high-quality option for forage growers.
Pest pressure can decrease the economic viability of an alfalfa harvest. One particularly devastating pest of alfalfa in Maryland is the potato leafhopper (Empoasca fabae). Potato leafhoppers migrate northward from the southern United States every spring, making the timing of management in the northeast very difficult. Additionally, potato leafhoppers can utilize many alternative host plants, some of which are also of agroeconomic value, such as soybeans and several other fruit and vegetable crops, and leafhoppers can reproduce multiple times during the growing season. To protect alfalfa from potato leafhopper damage (termed ‘hopperburn’), insecticides are often the only option for growers. As a perennial crop, serious pest pressure in one growing season could impact nitrogen fixation in subsequent growing seasons, further accelerating economic losses for growers.
Figure 1. Amount of fixed nitrogen in alfalfa stems and leaves. * represents significant differences between treatments. No Nitrate = No Nitrogen Fertilizer, Moderate Nitrate = Nitrogen Fertilizer Applied; E. fabae- = No Leafhopper Pressure, E. fabae+ = Leafhopper Pressure.
Therefore, in recent field and greenhouse experiments, we sought to determine the effect of potato leafhopper pest pressure on nitrogen fixation in alfalfa. We predicted pest pressure would negatively impact plant growth and carbohydrate production, resulting in reduced nitrogen fixation by rhizobia and uptake of fixed nitrogen by alfalfa. We also predicted losses in nitrogen content of alfalfa due to pest pressure could be offset by nitrogen fertilizer applications. To test our predictions in a field setting, we planted four combinations of small plots: 1) Fixing Cultivar + Nitrogen Fertilizer, 2) Non-Fixing Cultivar + Nitrogen Fertilizer, 3) Fixing Cultivar No Nitrogen Fertilizer, and 4) Non-Fixing Cultivar No Nitrogen Fertilizer. Fixing and non-fixing alfalfa cultivars were utilized to compare plants reliant on both nitrogen fixation and soil nitrogen with plants completely reliant on soil nitrogen. We split each plot in half, applying cages with leafhoppers to one side and cages without leafhoppers to the other. We analyzed the amount of fixed nitrogen in aboveground plant tissue. Results from the field experiment contradicted our predictions, showing nitrogen fertilizer did not increase aboveground nitrogen content of alfalfa under pest pressure. Nitrogen fertilizer (Moderate Nitrate) also decreased aboveground fixed nitrogen content in plants with and without pest pressure (Fig. 1). Unfertilized plants (No Nitrate), in contrast, showed significantly increased amounts of fixed nitrogen content when under pest pressure (Fig. 1). These results contradicted our predictions and suggest alfalfa interactions with rhizobia play a role in helping plants withstand pest damage.
We also examined leafhopper-alfalfa interactions in a greenhouse setting. Here, we analyzed the response of two different cultivars of alfalfa: leafhopper-susceptible (Pioneer 55V50) and leafhopper-resistant (Pioneer 55H94). Nitrogen fertilizer treatments were applied to both cultivars, as well as cages with or without leafhoppers. Results indicate that additional nitrogen fertilizer did not increase the percent nitrogen of plants under pest pressure, regardless of the cultivar (Table 1).
Overall, we conclude leafhopper pest pressure decreases total nitrogen content of alfalfa across all four cultivars tested in both field and greenhouse settings. Amending soils with additional nitrogen fertilizer did not offset losses to leafhopper pressure and we do not recommend this as a management strategy to growers. In our field experiment, however, we found evidence that leafhopper pressure enhances aboveground fixed nitrogen content of alfalfa grown in soils without additional nitrogen. Rhizobia may play an unexamined role in the response of alfalfa to leafhopper pressure. Broader implications of our results highlight how pest damage may increase nitrogen fixation, which may benefit farmers interested in utilizing nitrogen-fixing cover crops.
Acknowledgements: Many thanks to the Western Maryland Research and Education Center staff and greenhouse staff at the University of Maryland aiding in the execution of these experiments, as well as members of the Lamp Lab. This study was funded by Northeastern Sustainable Agriculture Research and Education (Award Number GNE18-187-32231) and the Hatch Project MD-ENTM-1802.
Table 1. Systemic (shoots, crowns, roots) percent nitrogen content of susceptible and resistant alfalfa cultivars in the greenhouse. No Nitrogen Added = No Nitrogen Fertilizer, Nitrogen Added = Nitrogen Fertilizer Applied; Healthy = No Leafhopper Pressure, Injured = Leafhopper Pressure.
