At-planting treatments for controlling early-season insect pests in corn

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

  1. 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).
  2. Afful, E., Illahi, N. & Hamby, K. Agronomy News. 10, 2–4 (2019).
  3. Reisig, D. & Goldsworthy, E. Efficacy of Insecticidal Seed Treatments and Bifenthrin In-Furrow for Annual White Grub, 2016. Arthropod Manag. Tests 43, 1–2 (2017).
  4. 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).
  5. 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
  6. Funayama, K. Influence of pest control pressure on occurrence of ground beetles (Coleoptera: Carabidae) in apple orchards. Appl. Entomol. Zool. 46, 103–110 (2011).

 

Department Issues Spotted Lanternfly Quarantine in Cecil and Harford Counties

Adult spotted lanternfly
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.

Download the department’s Spotted Lanternfly Quarantine Fact Sheet for more details about the quarantine.

Pyrethroid insecticide effects on pests and beneficials in field corn

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.

The herbicide timing compared two treatments:

  1. Herbicide alone (22 oz/acre Roundup WeatherMAX®, 0.5 oz/acre Cadet®, 3 lb/acre ammonium sulfate
  2. 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:

  1. Fungicide alone (Trivapro® 13.7 oz/acre)
  2. 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).
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.
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.
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/

 

Can Aboveground Pest Pressure Disrupt Nitrogen Fixation in Alfalfa?

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.

Special Alert: Growers Need to Scout for Soybean Podworms and Sorghum Headworms

Kelly Hamby1, Galen Dively1, David Owens2, Ben Beale3, Peter Coffey3, Andrew Kness3, Alan Leslie3, Erika Taylor3, Kelly Nichols3, Matthew Morris3, and Emily Zobel3

1University of Maryland Department of Entomology
2University of Delaware Extension Entomology
3University of Maryland Extension

Moth flight activity for the corn earworm, also known as the soybean podworm and one species of sorghum headworm, has increased during the past week. Pest pressure varies across the state and Delmarva region. The early surge in activity is attributed to the record temperatures during June and July, which have accelerated larval development and shortened the generation time of this insect. Corn earworm has already caused significant damage to ears of sweet corn and early planted field corn. Note that Bt hybrids expressing single or multiple Cry proteins no longer control earworms due to the development of resistance; only hybrids expressing the Vip3a Bt protein provide good ear protection. These hybrids represent a relatively small portion of the planted acreage. Thus, significantly more adult moths are now recruited in corn compared to levels a decade ago.

Corn earworms are strongly attracted to and prefer fresh corn silks for egg laying. Outbreaks in other crops often follow a midsummer drought, which causes the corn to ripen earlier and become less attractive to the moths. As early planted corn fields dry down, moths will move into other vegetable and grain crops.

Podworms in Soybeans:

Corn earworm feeding on soybean pod. Image: Clemson University
Corn earworm feeding on soybean pod.
Image: Clemson University

In soybeans, female corn earworm moths prefer to lay eggs in open-canopied, late-blooming fields, and are most attracted to soybeans for egg laying from flowering to early pod-set. Drought conditions also delay soybean maturity and prevent normal canopy growth, so peak moth activity is more likely to coincide with blooming of open-canopied fields. In irrigated fields, activity may be greater along pivot tracks and dry corners. Corn earworm larvae can damage flowers; however, because soybeans produce more flowers than needed, flowering sprays are rarely necessary. Podworms cause the most damage when large larvae are feeding on full seed pods with large seeds (see information from NCSU).

What to do? Scout bean fields, paying special attention to those fields with a more open canopy in areas where the nearby maturing corn is no longer attractive to earworm moths.

Sampling should start during mid-August and be repeated at least weekly in each field until a spray decision is made or the pods reach full maturity. Most fields are planted as narrow-row beans, so a 15-inch sweep net is the most practical way to sample for earworms. Walk along the rows, swinging the sweep net so that the opening passes through the foliage. The net is turned 180 degrees after each sweep as you advance with each step to swing the net through the foliage in the opposite direction. Each stroke is counted as one sweep. A series of 25 sweeps should be taken at each of 5 sites in every 40 acres.

Treatment is recommended when counts exceed 3 medium to large podworms per 25 sweeps in narrow row fields, or 5 podworms per 25 sweeps in wide row fields (20 inches or greater). The timing strategy is to wait until most of the larvae are 3/8 inch or more in length, and then treat when pod damage is first evident. This allows for most egg laying and hatching to occur before treatment and reduces the chances of a second spray being needed later. These static thresholds are based on long-term averages for control costs and soybean prices. North Carolina State extension has developed a dynamic online threshold calculator for corn earworm in soybeans that takes into account the sampling method (uses a 15 sweep rather than a 25 sweep sample), row spacing, cost for control, and the value of soybeans, which can be found at:

https://www.ces.ncsu.edu/wp-content/uploads/2017/08/CEW-calculator-v0.006.html

Since the 2008 season, numerous reports of control failures with pyrethroids (Group 3A) used for earworm control have been reported from the Mid-Atlantic region and states to our south. This insect has developed moderate to high levels of resistance to this class of insecticides, so growers need to consider other modes of action. If a pyrethroid (e.g., Brigade, Warrior, Mustang Maxx, Hero, Baythroid, Tombstone) is used, the highest labeled rate timed for small to medium, rather than large worms, is recommended. Alternative classes such as diamides (Group 28; e.g., Coragen, Prevathon), oxadiazines (Group 22A; e.g., Steward) and spinosyns (Group 5; e.g., Blackhawk, Radiant) will be most effective. These materials are also generally softer on beneficial insects which prey upon other late season soybean pests, such as soybean looper and stink bug. ALWAYS read and follow instruction on the pesticide label; the information presented here does not substitute for label instructions.

Headworms in Sorghum:

Corn earworm female in sorghum. Image: John C. French Sr
Corn earworm female in sorghum. Image: John C. French Sr

Headworms (corn earworm, fall armyworm, and sorghum webworm) are caterpillar pests that infest grain heads. Flowering or heading sorghum is attractive to corn earworm females for egg laying, and headworm issues have been reported in Southern Maryland this year. Headworms feed on the flowers and developing kernels and large larvae can cause significant yield loss.

What to do? Scout sorghum fields from the end of flowering until hard dough.

Sample heads by bending them into a clean white 5 gallon bucket and beating them to dislodge the headworms. Sample 10 heads per location and sample multiple locations per field. If most larvae are small (up to ¼ inch) sample the field again in 3 to 4 days.

Thresholds vary by the size and species of larvae and sorghum value. In general, 2 corn earworm larvae per head would warrant treatment, and Texas A&M has developed a dynamic online threshold calculator that incorporates cost of control, grain value, anticipated yield (heads/acre), and larval size, which can be found at:

https://agrilife.org/extensionento/sorghum-headworm-calculator/

As mentioned above, pyrethroids (Group 3A) offer poor to moderate control of corn earworm in the Mid-Atlantic, and will not control heavy infestations or large worms. If a pyrethroid (e.g., Brigade, Warrior, Mustang Maxx) is used, the highest labeled rate is recommended. Alternative classes such as diamides (Group 28; e.g., Prevathon), spinosyns (Group 5; e.g., Blackhawk, Tracer), or carbamates (Group 1A; e.g., Sevin, Lannate) will be most effective. Selective insecticides that are less damaging to beneficials are recommended, such as Prevathon (most recommended) or Blackhawk. ALWAYS read and follow instruction on the pesticide label; the information presented here does not substitute for label instructions.

While scouting for headworms, growers are encouraged to look for sugarcane aphid in sorghum as well. Virginia Tech reported the first confirmed identification of white sugarcane aphid in Amelia County on August 1st. For more information on sugarcane aphid see Agronomy News Volume 8 Issue 1. If sugarcane aphids are also present, we strongly advise using selective insecticides to preserve the natural enemies that slow sugar cane aphid population growth.

Further Resources:

North Carolina State Podworm Factsheet:

https://soybeans.ces.ncsu.edu/corn-earworm/

University of Delaware Weekly Crop Update:

https://sites.udel.edu/weeklycropupdate/

University of Delaware Insect Management:

http://extension.udel.edu/ag/insect-management/field-vegetables-fruit/

Virginia Tech Pest Management Field Crops Guide:

https://www.pubs.ext.vt.edu/456/456-016/456-016.html (Sorghum Headworm Section)

Sorghum Checkoff Headworm Guide:

https://www.sorghumcheckoff.com/newsroom/2016/03/28/headworms/

Sugarcane aphid found in VA sorghum – 2019:

https://blogs.ext.vt.edu/ag-pest-advisory/sugarcane-aphid-found-in-va-sorghum-2019/

Agronomy News Sugarcane Aphid Article:

https://extension.umd.edu/sites/extension.umd.edu/files/_docs/AgronomyNewsApril2017.pdf

Sulfoxaflor Registered for New Uses

The U.S. Environmental Protection Agency (EPA) has just issued a long-term approval for the insecticide sulfoxaflor, which the Agency has characterized as “an effective tool to control challenging pests with fewer environmental impacts.” The following information is from today’s EPA OPP Update.

“After conducting an extensive risk analysis, including the review of one of the agency’s largest datasets on the effects of a pesticide on bees, EPA is approving the use of sulfoxaflor on alfalfa, corn, cacao, grains (millet, oats), pineapple, sorghum, teff, teosinte, tree plantations, citrus, cotton, cucurbits (squash, cucumbers, watermelons, some gourds), soybeans, and strawberries.

EPA is providing long-term certainty for U.S. growers to use an important tool to protect crops and avoid potentially significant economic losses, while maintaining strong protection for pollinators,” said Alexandra Dapolito Dunn, assistant administrator for EPA’s Office of Chemical Safety and Pollution Prevention. “Today’s decision shows the agency’s commitment to making decisions that are based on sound science.”

Sulfoxaflor is an important and highly effective tool for growers that targets difficult pests such as sugarcane aphids and tarnished plant bugs, also known as lygus. These pests can damage crops and cause significant economic loss. Additionally, there are few viable alternatives for sulfoxaflor for these pests. In many cases, alternative insecticides may be effective only if applied repeatedly or in a tank mix, whereas sulfoxaflor often requires fewer applications, resulting in less risk to aquatic and terrestrial wildlife.

EPA’s registration also includes updated requirements for product labels, which will include crop-specific restrictions and pollinator protection language.

*Background*

In 2016, following a 2015 decision of the Ninth Circuit Court of Appeals vacating the registration of sulfoxaflor citing inadequate data on the effects on bees, EPA reevaluated the data and approved registrations that did not include crops that attract bees. The 2016 registration allowed fewer uses than the initial registration and included additional interim restrictions on application while new data on bees were being obtained. Today’s action, adding new uses, restoring previous uses, and removing certain application restrictions is backed by substantial data supporting the use of sulfoxaflor.

For additional information, please visit the EPA website.

Arrest These Early Season Soil Critters: Wireworm and White Grub Management

Edwin Afful, Nurani Illahi and Kelly Hamby
University of Maryland, Department of Entomology

white grub next to corn plant in field
Figure 1. Grub (circled) uncovered in field corn.

Spending most of their lives in the soil, they feed on our cherished seeds, and cause stand reductions that affect yield. Who are these critters and what can we do to save our seeds? White grubs and wireworms are a part of soil insect pest complex known to be culprits in the “covert stand reduction operation” in small grain and corn fields. Seed corn maggots, slugs, and cutworms can also cause early season stand reduction, and their damage can be distinguished from grubs and wireworms. The early developmental stages of grubs and wireworms occur on our blindside—in the soil. Larva of both species are the perpetrators of the illegal acts against our seeds, and there are no effective rescue treatments once damage is visible. Economic populations of these pests vary by season, depend upon a variety of factors, and are sporadic. In our recent studies we have not seen economic damage; however, control decisions should be based on pest history at your site and sampling information.

Identification

Close-up of white grub
Figure 2. Raster (arrow) of white grub.

White grubs are the immature stages of scarab beetles, and multiple species (1-3 year life cycle depending on species) occur and feed upon plant roots as they develop. They have a characteristic “C” shape (Fig. 1, circled), have 3 pairs of legs immediately behind their head, and the entire grub body measures 0.25-1 inch in length. They can be identified to species based on the pattern of the hairs on the underside of their end (“raster”, Fig. 2 arrow). For further information on identification and life cycles, see resources from Ohio State6 and Purdue4.

Wireworms are the immature stages of click beetles, and multiple species with different life histories occur in most grain growing regions. Wireworms chew into seeds and stems, leaving holes, dead spots, or hollowed out seeds on seedlings. They are 0.25-0.75 inches long and have slender semi-cylindrical or cylindrical bodies that can be a white, yellowish, or coppery color with three small pairs of legs behind the head. On their end, they have a flattened segment with a “keyhole-shaped” notch that can look similar to the chewing mouthparts on the head (Fig. 3).

wireworm
Figure 3. Close up image of wireworm showing the “keyhole-shaped notch” that occurs at the rear.

Damage

Grubs and wireworms both cause stand reduction; however, there are some distinguishable differences. Damage by wireworms and grubs are usually confined to certain areas of a field where populations are high or where soil conditions were optimum for egg laying and larval development.

White grubs feed on roots, chewing off the fine hairs on the roots. This reduces root uptake of water and phosphorus, resulting in aboveground symptoms of wilting and purpling of the stem. Severely infested fields often suffer stand loss when injured plants die.

Wireworms typically feed on the germ of corn kernels or hollow out the kernel, killing the plant. Wireworms may also cut off small roots or tunnel into the underground portions of the root or stem of young corn plants. If feeding is above the growing point, holes will appear in the leaves above ground.

Sampling

Sampling must occur before tilling and planting and should be done once it warms up enough for grubs and wireworms to be active at the soil surface (soil temperature at 6 inch depth >45 °F)3, 7. One to two samples should be taken per 10 acres with no less than 5 locations per field. To sample, dig out a 1-foot square 6 inches deep and dump the soil in a tray or sift it with ¼” hardware cloth to look for grubs and wireworms. While economic thresholds have not been established, an average of 1 white grub and/or wireworm per square foot would warrant an at-planting or seed treatment insecticide3, 7.

Management

Cultural management:  Rotation is the most effective, and often the lowest cost, cultural tactic for reducing many grub and wireworm problems. Both grubs and wireworms prefer grass hosts, and rotation of corn and small grains with a non-grass crop reduces populations; however, weeds must be controlled to ensure there are no host plants. Planting under warm conditions allows seeds to germinate rapidly and plants may outgrow wireworms. Certain species of wireworms are abundant only in poorly drained soils; therefore, proper drainage of soils can reduce the wireworm threat. The use of starter fertilizer, timely planting, and effective weed management will also help reduce white grub and wireworm damage2.

Biological control:  Organisms such as birds, parasitic nematodes, and fungal pathogens prey on white grubs and wireworms. The effectiveness of two beneficial nematodes were studied on turfgrass against grubs in California with some success1. Further research is required to effectively use biological control for these pests.

Figure 4. Mean control rating against white grubs across a varying number (N) of trials. Unpublished data from Dr. Dominic Reisig at North Carolina State University.

Chemical Control: There are no effective rescue treatments once white grub and wireworm damage is visible. However, commercial seed treatments and at-planting insecticides have varying effectiveness for grub and wireworm protection prior to damage. Dr. Dominic Reisig at North Carolina State University has been performing efficacy trials in field corn with grub and wireworm pressure, and has rated a variety of products against each based on his results. The N values indicate the number of trials each product was used in, and the values are a rating from 0 (no control) to 9 (excellent control), with the best performance products in dark red. Most products and rates provide fair control of grubs5, with heavy grub pressure requiring a higher seed treatment rate or in-furrow applications of Capture® (pyrethroid insecticide; Fig. 4). Wireworms require at least a 500 rate of seed treatment for fair control, with slightly better control at the 1250 rate (Fig. 5).

Figure 5. Mean control rating against wireworms across a varying number (N) of trials. Unpublished data from Dr. Dominic Reisig at North Carolina State University.

Further Reading/ References

Koppenhöfer,A.M., Wilson,M.,  Brown, I., Kaya, H.K., and R. Gaugler, Biological Control Agents for White Grubs (Coleoptera: Scarabaeidae) in Anticipation of the Establishment of the Japanese Beetle in California, Journal of Economic Entomology, Volume 93, Issue 1, 1 February 2000, Pages 71–80, https://doi.org/10.1603/0022-0493-93.1.71

NC State extension: Managing Insect Pests in Organically Certified Corn: https://entomology.ces.ncsu.edu/managing-pests-in-organically-certified-corn/

Owens, D., and B. Cissel. Insect Management in Field Corn – 2018: https://cdn.extension.udel.edu/wp-content/uploads/2018/05/02095804/Insect-Management-In-Field-Corn-20181.pdf

Purdue University Field Crops IPM. White Grubs: https://extension.entm.purdue.edu/fieldcropsipm/insects/corn-whitegrubs.php

Reisig, D., and E. Goldsworthy. Efficacy of Insecticidal Seed Treatments and Bifenthrin In-Furrow for Annual White Grub, Arthropod Management Tests, Volume 43, Issue 1, 2018, tsx135-136

https://academic.oup.com/amt/article/43/1/tsx135/4781660

https://academic.oup.com/amt/article/43/1/tsx136/4781661

https://academic.oup.com/amt/article/43/1/tsx137/4781662

Shetlar, D.J., and J. Andon. Identification of White Grubs in Turfgrass: https://ohioline.osu.edu/factsheet/hyg-2510

Whalen, J., and B. Cissel. Soil Insect Management in Field Corn: http://extension.udel.edu/factsheets/soil-insect-management-in-field-corn-2/

 

Guess the Pest! Week #24 Answer: European Corn Borer

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Bill Cissel, Extension Agent – Integrated Pest Management, University of Delawarebcissel@udel.edu

Congratulations to Grier Stayton for correctly identifying the insect as a European corn borer and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #24 Answer: European Corn Borer

It’s hard to believe that a pest that once caused an estimated annual economic loss of $1 billion dollars in the United States is now a rare occurrence. The European corn borer (ECB), as the name implies, is actually native to Europe and was introduced into North American in the early 1900s. In addition to being a pest of corn (field corn and sweet corn), it is also considered a pest of many vegetable and field crops. Since the adoption of transgenic corn hybrids in the mid-1990s, losses due to ECB have been virtually eliminated in Bt crops and significantly reduced in other vegetable and non-Bt field crops. This is one of the pests that the UD Insect Trapping Program monitors with black light traps. The reason we continue to monitor ECB populations throughout the state is because even though generally speaking, populations have been low, there are still local pockets where ECB is causing damage. The photo above of the ECB larva was taken on the Eastern Shore of VA by Helene Doughty from a non-BT sweet corn plot that was 100% infested with ECB.

For information on the benefits of Bt adoption, read this article: Regional pest suppression associated with widespread Bt maize adoption benefits vegetable growershttp://www.pnas.org/content/early/2018/03/06/1720692115

Guess the Pest! Week #22 Answer: Helicoverpa zea, Corn Earworm

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Bill Cissel, Extension Agent – Integrated Pest Management, University of Delawarebcissel@udel.edu

Congratulations to Amanda Heilman for correctly identifying the insect as an adult corn earworm and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #22 Answer: Helicoverpa zea, commonly known as corn earworm

The moth in the photograph is an adult Helicoverpa zea, commonly referred to as a corn earworm. The adult moth is a nectar feeder and not considered a pest. However, corn earworm larvae are considered by some to be the most economically important crop pest in North America. They are highly polyphagous meaning they feed on many different species of plants. Corn, especially sweet corn, is a preferred host plant. However, they also attack soybean, sorghum, snap bean, tomato, and cotton to name a few. Larvae prefer to feed on reproductive plant structures including blossoms, buds, and fruits. It is because of this large host range, and the fact that Helicoverpa zealarvae are so destructive that they are known by several other common names including tomato fruitworm, cotton bollworm, and podworm.

For the latest trap counts for corn earworm in your region, visit mdmothmap.com.

Guess the Pest! Week #20 & 21 Answer: Trissolcus japonicus

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Bill Cissel, Extension Agent – Integrated Pest Management, University of Delawarebcissel@udel.edu

Congratulations to Greg Hawn (week 20 winner) and to Joseph Streett (week 21 winner) for correctly identifying the insect as Trissolcus japonicus and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #20 – 21 Answer: Trissolcus japonicus
Bill Cissel, Extension Agent – Integrated Pest Management, Joe Kaser, Research Associate, USDA-ARS Beneficial Insects Introduction Research, and David Owens, Extension Entomologist

Trissolcus japonicus, a tiny wasp commonly referred to as the Samurai wasp, is an egg parasitoid of the invasive brown marmorated stink bug (BMSB). This particular species is native to Asia and has been in quarantine since 2007 and under evaluation for potential release as a classical biological control agent. In 2014, wild populations of Trissolcus japonicus, slightly different from the ones that were in quarantine, were detected in Beltsville, MD and since, additional discoveries have been made throughout the region, including Washington, D. C., Virginia, West Virginia, Pennsylvania, New Jersey, Ohio, and Delaware. It is believed that Trissolcus japonicus may have hitchhiked a ride in a BMSB egg mass that was on plant cargo shipped from Asia, but it is difficult to say exactly how it got here. In fact, it appears that the samurai wasp has hitchhiked here more than once!

A single Trissolcus japonicus female is capable of parasitizing an entire BMSB egg mass which typically contains ~28 eggs. When the male parasitoids emerge, they wait on the egg mass for the females to emerge so they can mate. They are capable of having up to ten generations per year.

To help with reducing BMSB populations in Delaware, we partnered with some of the folks at the USDA Beneficial Insects Introduction Research Laboratory in Newark, DE to redistribute Trissolcus japonicas throughout the state. When I share that we are releasing a parasitic wasp to help with BMSB control, the first reaction that I typically get is, “Will it sting me?” If you look at the photo with some wasps on the dime, you will understand why this is not a concern. Hopefully, this tiny wasp will live up to its name as the Samurai wasp and do its part in controlling BMSB.

Fun Entomology Fact: A female Trissolcus japonicus will chemically mark the BMSB eggs that she laid eggs in and defend them against other parasitoids.

Here is a link to a very informative fact sheet from UF on Trissolcus japonicushttp://entnemdept.ufl.edu/creatures/beneficial/wasps/Trissolcus_japonicus.htm