Progress report for GNE20-230

Project Type: Graduate Student
Funds awarded in 2020: $14,961.00
Projected End Date: 07/31/2022
Grant Recipient: University of Maryland
Region: Northeast
State: Maryland
Graduate Student:
Faculty Advisor:
Dr. Kelly Hamby
University of Maryland College Park
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Project Information

Summary:

Corn growers have several options for at-planting pest control, including neonicotinoid seed treatments (NSTs), pyrethroids that can be applied in the planting furrow, and corn hybrids with plant incorporated protectants sourced from Bacillus thuringiensis bacteria (Bt); growers may also use all three together. Because these treatments target similar pests, using multiple products can be redundant. Targeting insect control and using the most effective product could reduce insecticide use, thereby increasing environmental sustainability and decreasing input costs. Insecticide treatments can also disrupt biological control. For example, NSTs can reduce slug predator populations in soybeans, causing economically damaging outbreaks of slugs. Because slugs are a concern in the Mid-Atlantic and difficult to control, it is important to determine if at-planting insecticides similarly impact biological control of slugs in corn. Lower corn prices may increase adoption of less expensive non-Bt corn, which has a unique pest complex for which at-planting applications must also be optimized. To improve pest management decision making in corn, we will conduct separate field studies using Bt and non-Bt hybrids and evaluate the impacts of NSTs and in-furrow pyrethroids on pest control by measuring pest pressure and damage to seedlings. Because treatments may disrupt slug biological control, we will also measure slug abundance, slug predator abundance, and slug predator activity. Finally, we will compare yield and quantify ear pest pressure. Results will be disseminated through extension presentations and publications, enabling growers to plan targeted early-season pest control programs for more financially and environmentally sustainable corn production.

Project Objectives:

My goal is to provide information to help growers to tailor early season pest control tactics to their needs, increasing sustainability and profitability. In order to achieve this, my specific objectives are to:

(1) Determine how NSTs and in-furrow pyrethroids affect pest pressure and damage when used against pest complexes in three Maryland growing regions in separate Bt and non-Bt corn fields.

(2) Determine the impact of NSTs and in-furrow pyrethroids on biological control of slugs by measuring slug damage, slug predator abundance, and predation rates on slugs in three Maryland growing regions

(3) Determine the impacts of NSTs and in-furrow pyrethroids on yield and evaluate late season ear and stand damage in three Maryland growing regions using separate in Bt and non-Bt corn fields.

Introduction:

The purpose of this project is to increase the sustainability and efficiency of early-season pest control in Mid-Atlantic corn production by comparing at-planting management options in Bt and non-Bt hybrids. Growers can use multiple insect management products, including neonicotinoid insecticide seed treatments (NSTs),  in-furrow pyrethroid insecticides, and Bt corn hybrids [1–3]. NSTs and in-furrow pyrethroids control assorted soil and seedling pests [4, 5], with significant overlap in their spectrum of control. In the Mid-Atlantic, these applications primarily target soil pests such as white grubs and wireworms [4, 7].  NSTs, pyrethroids, and Bt traits all target multiple lepidopteran pests, including black cutworm and armyworm [4, 6, 7]. Because these products were developed for corn belt pest complexes and target similar pests, comparing efficacy against Maryland pest complexes will allow growers to choose the most effective treatment and eliminate redundant insecticide applications.

In addition to their inherent redundancy, insecticides do not provide yield benefits if target insect pest pressure is too low [9–13]. Many of the pests targeted by NSTs and in-furrow pyrethroids are sporadic and do not occur in economically important numbers in every field every year [13]. Preliminary data suggest that Maryland corn experiences relatively low pest pressure (Fig. 1). Lepidopteran pests especially have declined following wide-spread Bt corn adoption [6]. However, Maryland is a geographically diverse state, so regional pest pressure varies (Fig. 1). Additionally, soil pests are difficult to scout and impossible to control with rescue treatments [2], so at-planting treatments can be valuable in fields where soil pest pressure is anticipated. By measuring how treatments affect pests in different locations in Maryland we will determine the conditions and regions where applications are warranted and where they can be avoided, further reducing insecticide use.

At-planting insecticides may also disrupt biological control and negatively impact non-target organisms. Biodiversity in agricultural systems provides pest suppression [14]. Non-target impacts to biocontrol organisms can cause secondary pest outbreaks, complicating pest management and potentially reducing yields [24, 15]. Impacts to non-target organisms have been associated with NSTs [9, 16–19] and foliar pyrethroid applications [20–23], although there are few studies on pyrethroids applied in the planting furrow. In soybeans, NSTs disrupt biological control of slugs [28], a key pest in Maryland corn (Table 1).  Measuring the impact of at-planting insecticides on slugs and slug predators will help clarify how the treatments impact biological control of slugs in corn. This information will allow growers to conserve slug predators and better control these difficult to control pests.

Better understanding of how NSTs and in-furrow pyrethroids contribute to pest management will significantly improve on-farm decisions. Because falling grain prices may also incentivize planting less expensive corn lacking Bt traits, which experience a different pest complex [24], we will evaluate at-planting insect pest control in both Bt and non-Bt hybrids. Our results will allow growers to optimize profitability and environmental sustainability by selecting the treatments most suited to their pest pressure and production system, reducing unneeded insecticide applications, and enhancing biodiversity and biocontrol.

Research

Materials and methods:

To account for variability in weather, pest pressure, and other factors, research will be replicated across three growing seasons (2020-2022).

In 2020, to investigate the pest and non-target impacts of insecticides applied at-planting in corn, three different treatments were evaluated: (1) bare, untreated seed with no insecticide applied in-furrow, (2) seed treated with the NST Poncho (active ingredient clothianidin), and (3) bare, untreated seed with the pyrethroid Capture LFR (active ingredient bifenthrin) applied in-furrow.

The three treatments were arranged in a Latin Square with three replicate plots a minimum of 200 ft in length consisting of a minimum of 24 rows at 30 inch spacing (60 ft) (Fig. 2). Plots were established following this design for the Bt hybrid, LC1196 VT2P (Local Seed, Memphis, TN) and the non-Bt hybrid, P1197LR (Pioneer Hi-bred International, Inc. Johnston, IA). Both hybrids are considered high yielding and have similar maturity dates. Because the Bt and non-Bt varieties were not isolines, and because plots were planted in different fields, they are treated as separate studies and analyzed independently from one another.

Fig. 2. Plot plan

To test these treatments under differing pest pressure across the region, we replicated the research at three Maryland research farms: Central Maryland Research and Education Center (Beltsville, MD), Wye Research and Education Center (Queenstown, MD), and Western Maryland Research and Education Center (Keedysville, MD). In 2020, Queenstown was planted on May 14th, Keedysville on May 19th, and Beltsville on May 21st.

Objective 1. Determine how NSTs and in-furrow pyrethroids affect pest pressure and damage when used against pest complexes in three Maryland growing regions using separate in Bt and non-Bt corn fields.

    To evaluate the impact that NSTs and in-furrow pyrethroids have on soil pests at planting, we sampled seedlings in the V2-V4 growth stage 3-4 weeks after planting (Queenstown on June 3rd and 4th, Keedysville on June 8th, and Beltsville on June 10th). We sampled stand (the number of healthy and stunted plants in 50 ft of row) in three locations in all plots. Plants estimated to be less than half the size of the average healthy plants, but without signs of serious pest damage, were considered stunted. We excavated plants with signs of soil pest damage (yellowing or wilting of center leaves or entire plant) to confirm presence of soil pests (figure 3a). If identifiable feeding damage or the pest itself was present, plants were categorized as damaged by soil pests. We classified foliar pests feeding by pest category: lepidopteran chewing damage which included signs of cutworm (holes in rows) or armyworm (leaf-margin feeding), slugs (rasping that removes leaf tissue in this stripes), and non-lepidopteran foliar feeding (abnormal growth from piercing-sucking damage, small feeding holes from leaf beetles) (figures 3b-f). Only one type of damage, whatever affected the greatest area, was recorded per plant. In 2020 we did not record the area of damage for individual plants.  

Fig. 3a-f. Diagnostic signs of pest damage. a) soil pest, b) cutworm, c) armyworm, d) slug, e) stinkbug, and f) flea beetle

            We performed separate analyses for Bt and non-Bt experiments. Stand counts from the subsamples were summed and then were converted to the number of plants per acre and analyzed using JMP Pro 14. Treatment, location, and the treatment by location interaction were included in the model. The interaction term was dropped when insignificant. Pest damage data were summed across subsamples and converted to the percentage of plants damaged by replicate plot. These were also analyzed using JMP Pro 14. Assumptions of normality and homogeneity of variances were checked, and models weighted by the variance of the most unequal variable were run when necessary.

Objective 2. Determine the impact of NSTs and in-furrow pyrethroids on biological control of slugs by measuring slug damage, slug predator abundance, and predation rates on slugs in three Maryland growing regions

To determine whether NSTs and pyrethroids impact slug pressure in corn, we sampled slug activity-abundance, slug predator activity-abundance, and predation by slug predators (rates of slug feeding was measured during foliar sampling for Objective 1). All sampling for slugs and slug predator activity abundance took place overnight when slugs are most active [30]. The majority of our sampling occurred within 4 weeks of planting when slugs impact corn yields [35]. We measured slug activity abundance following the procedure described by Raudenbush et al. [36] who found that the addition of a pitfall trap to the traditional shingle trap increased captures. Traps consisted of nested 16 oz cups (WebstrauntStore, Lancaster, PA), sunk into the ground, filled with soapy water. These were covered with a 1 ft2 roof shingle secured with a heavy stone. We placed two slug traps at two locations per plot and counted slugs once a week for eight weeks following planting. We checked slug traps in the morning when temperatures were lower, roughly between 7:00 and 11:00 AM on every date except for July 15th in the non-Bt plots at Queenstown, which were sampled between 11:20 and 12:10 PM. We inspected the area under the shingle footprint, within the pitfall trap, and under the pitfall trap for slugs and slug eggs, and the number of each recorded. The soapy water solution was replaced after sampling each week. No slug eggs were found in any treatment throughout the sampling period

            We measured slug predator activity abundance using dry pitfall traps at Queenstown one and two weeks after planting. These consisted of nested 16 oz cups (WebstrauntStore, Lancaster, PA), sunk into the ground and covered with 1 ft2 of stiff plastic. Three carriage bolts were attached to each plastic square, allowing them to be secured in the soil and slanted for water runoff. We placed two pitfall traps per plot. Pitfall traps were deployed for 12 hours overnight, corresponding with the first two deployments of sentinel prey (described below) at Queenstown. Trap contents were collected in the morning and immediately be frozen and stored at -80° C to allow for future possible gut content analysis to determine if the natural enemies had fed on slugs. After the two dates at Queenstown, we used antifreeze-filled traps for all dates and locations in order to increase capture, and plan to use this approach in the future. Pitfall traps were collected weekly, filtered, and contents stored in 70% ethanol. Taxa credited with slug control [30, 36, 37] will be counted and carabid beetle specimens will be identified to species to differentiate between feeding guilds [38] (Fig. 4).

Fig. 4. Preparing pitfall trap samples for beetle identification

            The activity of slug predators was measured using sentinel prey. We used waxworm caterpillars, Galleria mellonella L., as a stand-in for slugs [38], because of difficulty in restraining slugs and as predation on G. mellonella correlates with large carabids that are often slug predators [28]. Five healthy waxworm larvae (Grubco, Fairfield, OH) were secured to index cards (four cards per plot) using double-sided hem tape (Jo-Ann Stores LLC, Hudson, OH) and clear scotch tape. Index cards were prepared the day of deployment and transported to the field in a cooler with ice packs. To exclude vertebrate predators, index cards were placed in circular cages made from 0.5 inch mesh, 19-gauge hardwire cloth (The Home Depot Inc, Atlanta, GA) secured to the ground with two ground staples [38]. Cages were covered with clear 6 inch by 0.5 inch petri dishes (Fig. 5), and 4 cages were deployed per plot. Waxworms were deployed in the field for approximately 12 hours overnight and collected in the morning and immediately evaluated or frozen for later evaluation. Larvae showing signs of damage were counted, and the number of intact, predated, and missing larvae per plot were recorded.

Fig. 5. Sentinel prey cage

Separate analyses were performed for Bt and non-Bt experiments. The activity density of slugs was compared by summing captures per trap and averaging the captures between the two traps in each plot. Then captures per treatment were analyzed by ANOVA specifying treatment and location as random variables. Slug seedling damage was analyzed by the same method as described for seedling damage in Objective 1. Sentinel prey data will be analyzed with logistic regression. Slug predator abundance will be analyzed by linear mixed model.

Objective 3. Determine the impacts of NSTs and in-furrow pyrethroids on yield and evaluate late season ear and stand damage in three Maryland growing regions using separate in Bt and non-Bt corn fields.

            While NSTs and pyrethroids applied at-planting will not affect ear damage, Bt controls lepidopteran stalk and ear pests. To better understand ear pest pressure and damage given regional pest suppression [32, 33], we sampled ears for pest damage. Queenstown was sampled on August 7th, Keedysville on August 10th, and Beltsville on August 14th.  At soft dough stage, ten consecutive ears were sampled in four locations in each plot. Ears were removed from the stalk, husk removed, and the area of kernels damaged was counted in cm2 using a transparent grid to estimate area (Fig. 6.). Damage was classified as (1) caterpillar damage, (2) stink bug damage, and (3) sap beetle damage. Any pests present were identified and recorded.

Fig. 6. Measuring ear damage.

Stand count was also recorded shortly prior to harvest to determine if stand was lost to stalk pests over the course of the season. The number of stunted (those too small to make an ear) and non-stunted corn plants in 50 ft of row were counted in three locations in each plot, and stand per acre was calculated. The whole plot was harvested by a combine harvester. Yield was taken at harvest by the combine or placed in a weigh wagon, based on the equipment at each farm, and converted to bushels per acre corrected to 15.5% moisture.

All data were analyzed separately in Bt and non-Bt experiments. Subsamples of ear damage (severity and incidence) and stand were summed at the plot level, and the percent of ears damaged was calculated for incidence. Severity, incidence, stand, and yield were compared between insecticide treatments by ANOVA specifying treatment and location as random variables.

Research results and discussion:

Results and discussion

Objective 1: Determine how NSTs and in-furrow pyrethroids affect pest pressure and damage when used against pest complexes in three Maryland growing regions in separate Bt and non-Bt corn fields.

Non-Bt corn stand. We saw minor differences in pest pressure and damage between treatments. In general, pest pressure was very low. In non-Bt corn, seedling stand was not affected by treatment; insecticide treatments did not increase stand compared to the untreated control (Fig. 7). Stand was not different between farms.

Fig. 7
Fig. 7. Mean number of plants per acre measured visually in non-Bt plots in V2-V4. 150 ft of row was sampled for each plot. Stand count did not statistically differ between treatments. 

Non-Bt corn pest pressure. The proportions of plants with soil pest and caterpillar (cutworm and armyworm) damage were significantly affected by treatments (Table 2). Poncho 250 had lower percentages of both soil pest and caterpillar damage compared with the control. Capture LFR also had lower caterpillar damage compared to the control. Other chewing pest damage was not affected by the treatments. Overall, we saw very low pest pressure; although there are not treatment thresholds for soil pests at this growth stage, less than 1% of plants showed signs of soil pests in any treatment. The lack of differences in seedling stand count also suggests that soil pest pressure was low enough to not impact stand. We also saw almost no cutworm damage (the majority of caterpillar damage was from armyworm), and armyworm damage was below the 25% of plants damaged which is the action threshold for armyworm in seedling corn.

Table 2
Table 2. Percent of the stand damaged by pests as measured visually in non-Bt plots in V2-V4. 150 ft of row was sampled for each plot. Means followed by different letters indicate that they are statistically significant (p=0.05) from other means in the same column.

Caterpillar pressure was also significantly affected by location (Fig. 8) and the location by treatment interaction (Table 3). Keedysville had more caterpillar damage than the other research farms, and the control treatment at Keedysville had higher percentages of damage than the other treatments and other farms. Based on these results, it is clear that pest pressure is distributed unevenly across different regions of Maryland. Further, Capture LFR and Poncho 250 can be effective at reducing damage if caterpillar pressure is present.

Fig. 8
Fig. 8. The percent of stand damaged by caterpillar pests (cutworm and armyworm species) as measured visually in non-Bt plots in V2-V4. 150 ft of row was sampled for each plot. Locations with different letters indicate that they are statistically significant (p=0.05) from other locations.
Table 3
Table 3. Percent of the stand damaged by pests as measured visually in non-Bt plots in V2-V4. 150 ft of row was sampled for each plot. Means followed by different letters indicate that they are statistically significant (p=0.05) from other means in the same column.

Bt corn stand. In contrast to non-Bt corn, the stand count for Bt corn was impacted by treatments (Fig. 9). Poncho 250 had higher stand compared to the control treatment. Capture LFR was not significantly different from the other two treatments.

Fig. 9
Fig. 9. Mean number of plants per acre measured visually in Bt plots in V2-V4. 150 ft of row was sampled for each plot. Treatments with different letters are statistically significant (p=0.05) from other treatments.

Bt corn pest damage. There were few differences in pest damage between treatments in Bt corn. We did see significant differences in the percent of plants damaged by cutworm and armyworm (fewer plants were damaged in the Poncho 250 treatment compared to the control treatment, and Capture LFR was not significantly different from either), but the percentages of plants damaged by soil pests and non-caterpillar chewing pests were not affected by treatments (Table 4). The fact that we did see treatment differences in the Bt corn suggests that Bt traits are not completely redundant with insecticides. Across treatments, the percentage of plants damaged was well below economic thresholds, as it was in non-Bt corn.

Table 4
Table 4. Seedling pests: Percent of the stand damaged by pests as measured visually in V2-V4 Bt corn. 150 ft of row was sampled for each plot. Means followed by different letters indicate that they are statistically significant (p=0.05) from other means in the same column.

Caterpillar pressure in Bt corn followed the same regional trends as in the non-Bt corn; Keedysville had much higher armyworm pressure than the other locations (Fig. 10). Unlike the non-Bt corn, the location by treatment interaction was not significant, and treatments performed similarly across the locations. These results continue to confirm the heterogeneity in pest pressure across Maryland and the importance of testing treatments at multiple study sites.

Fig. 10
Fig. 10. The percent of stand damaged by caterpillar pests (cutworm and armyworm species) as measured visually in Bt plots in V2-V4. 150 ft of row was sampled for each plot. Locations with different letters indicate that they are statistically significant (p=0.05) from other locations.

Objective 2. Determine the impact of NSTs and in-furrow pyrethroids on biological control of slugs by measuring slug damage, slug predator abundance, and predation rates on slugs in three Maryland growing regions.

Slug counts. In both non-Bt and Bt corn, abundance differed significantly between locations, but not between treatments. In non-Bt corn, Keedysville had the most slugs, Queenstown had fewer slugs, and Beltsville had the least with very low counts (fewer than five total) (Fig. 11).

Fig. 11
Fig. 11. The mean total of slugs counted in soapy water pitfall traps in non-Bt corn at three University of Maryland Research farms. Counts were taken weekly for 8 weeks after planting. Locations with different letters indicate that they are statistically significant (p=0.05) from other locations.

Slug counts in Bt corn followed a similar trend, where there was significant variation between locations but not between treatments (Fig. 12). Queenstown had the highest season totals, followed by Keedysville, and then Beltsville. At each location corn hybrids were planted in different fields. Slug abundance is likely controlled by field-level factors like previous crops, residue management, and drainage. This is likely why Keedysville had the highest slug abundance in of the Non-Bt corn while Queenstown had the highest for Bt corn.

Fig. 12
Fig. 12. The mean total of slugs counted in soapy water pitfall traps in Bt corn at three University of Maryland research farms. Counts were taken weekly for 8 weeks after planting. Locations with different letters indicate that they are statistically significant (p=0.05) from other locations.

Slug damage. Slug damage was not significantly impacted by treatment or location for either corn hybrid. Slug damage tended to be low. Below 5% of plants were damaged in all locations and treatments, except for non-Bt corn at Keedysville, where damage ranged from 3.6-12%. Even where it was higher, slug damage did not appear to damage the growing point of the corn otherwise reduce stand.  

Predation. Predation ranged from 5-62% across the corn hybrids, treatments, and farms. Although analysis is ongoing for these data, it is clear that there was at least some level of predation taking place, and this was coming from arthropod predators such as those seen while sampling (Fig. 13a-b)

Fig. 13
Fig. 13. Slug predators feeding on sentinel prey in 2020. a) Carabid beetle, b) wolf spider.

In non-Bt corn, predation tended to increase with time, with a trend of higher predation rates three weeks after planting than two weeks although this may not be significant (Figs. 14 & 15). All farms had similar levels of predation, despite the significant differences in slug abundance between farms observed above.

Fig. 14
Fig. 14. The ratio of sentinel larvae consumed to remaining larvae in three insecticide treatments in non-Bt corn at three University of Maryland research farms two weeks after planting. 20 sentinel larvae were deployed for each plot.
Fig. 15
Fig. 15. The ratio of sentinel larvae consumed to remaining larvae in three insecticide treatments in non-Bt corn at three University of Maryland research farms three weeks after planting. 20 sentinel larvae were deployed for each plot.

Predation trends were similar in Bt corn (Figs. 16 and 17), although predation did not increase as much in the third sampling week.

Fig. 16
Fig. 16. The ratio of sentinel larvae consumed to remaining larvae in three insecticide treatments in Bt corn at three University of Maryland research farms two weeks after planting. 20 sentinel larvae were deployed for each plot.
Fig. 17
Fig. 17. The ratio of sentinel larvae consumed to remaining larvae in three insecticide treatments in Bt corn at three University of Maryland research farms three weeks after planting. 20 sentinel larvae were deployed for each plot.

Objective 3. Determine the impacts of NSTs and in-furrow pyrethroids on yield and evaluate late season ear and stand damage in three Maryland growing regions using separate in Bt and non-Bt corn fields.

 

Non-Bt corn yield. At planting insecticides did not impact yield in non-Bt corn (Fig. 18). Given our results in Objective 1, this is probably due to low pest pressure. This fits with our previous research on Maryland pest pressure and suggests that in non-Bt corn at-planting insecticides could be scaled back without yield loss.

Fig. 18
Fig. 18. 2020 mean non-Bt corn yield (bu/ac) corrected to 15.5% moisture. There were no significant differences between treatments.

Non-Bt corn ear pests. At planting insecticides do not affect ear pest pressure, and treatments did not differ in percent damaged (Table 5) or severity (Table 6). Beltsville had more corn earworm and sap beetle damage compared to the other locations, and Keedysville had more stink bug damage than the other sites.

Table 5
Table 5: Percent of ears damaged during the soft dough stage by corn earworm (CEW), stink bugs, and sap beetles in non-Bt corn. 40 ears were visually assessed for each plot. There were no significant differences between treatments.
Table 6
Table 6: The mean area of damaged kernels (cm2) per ear during soft dough by corn earworm (CEW), stink bugs, and sap beetles in non-Bt corn. 40 ears were visually assessed per plot. There were no significant differences between treatments.

 

Non-Bt corn late stand. We saw no difference in late season stand between treatments. Late season stand was somewhat lower than early-season stand, but there was no evidence that pests past the seedling stage were impacting stand. Over all, we saw no evidence that early season insecticide use protects the plant long-term or translates to yield benefits.

Bt corn yield. As in non-Bt corn, there were no yield differences between treatments (Fig. 19).

Fig. 19
Fig. 19. 2020 mean Bt corn yield (bu/ac) corrected to 15.5% moisture. There were no significant differences between treatments.

Bt corn ear pests. Early season treatments do not control ear pests, and CEW has developed resistance to multiple Cry toxins. Unsurprisingly, treatments did not differ in the proportion of ears damaged (Table 7) or the amount of damage (Table 8). As with the non-Bt corn, Beltsville had higher numbers of corn earworm and sap beetle infested ears, and Keedysville had more stink bug damage.

Table 7
Table 7. Percent of ears damaged during the soft dough stage by corn earworm (CEW), stink bugs, and sap beetles in Bt corn. 40 ears were visually assessed per plot. There were no significant differences between treatments.
Table 8
Table 8. The mean area of damaged kernels (cm2) per ear during soft dough by corn earworm (CEW), stink bugs, and sap beetles in Bt corn. 40 ears were visually assessed per plot. There were no significant differences between treatments.

Bt corn late stand.  As with the non-Bt corn, Bt corn showed no differences in stand at the end of the season. Stand was slightly lower than early season stand, but did not indicate significant pressure from stalk-boring pests after the seedling stage. The lack of difference at the end of season was also notable after the significant differences in seedling stand seen in Objective 1. It suggests that although significant, the initial increase in stand in Poncho 250 plots compared to the control did not persist for the full season.

 

 

Research conclusions:

Objective 1 conclusions. Our 2020 results in non-Bt and Bt corn suggest that seedling pest pressure in Maryland tends to be low. Although it varied regionally, even at the highest, pressure did not cross economic thresholds. This lack of economically important pest pressure is backed up by a lack of yield differences shown in Objective 3. Even where stand was increased by using the NST treatment in Bt corn this did not translate to yield gains. Further, pest pressure was highest for caterpillar pests which are easily scouted for and which can be controlled with sprays if economic thresholds are reached. While yearly variation in pest pressure is likely, the low pressure and pest composition across our sites in 2020 suggest that prophylactic insecticides could be skipped in both non-Bt and Bt corn in order to minimize input costs and non-target risks. 

Objective 2 conclusions. Several important data sets for this objective are still being analyzed, and pitfall traps measuring predator activity abundance are still being processed. With the data currently analyzed, there is no evidence that at-planting insecticide use is flaring slug populations or causing increases in slug damage to corn seedlings. These preliminary results suggest that growers may be able to use NSTs and in-furrow pyrethroids without exacerbating slug problems, but it is necessary to analyze predation and predator abundance data.

Objective 3 conclusions. At-planting insecticides did not result in yield gains compared to untreated corn with no in-furrow application. This was true for both non-Bt and Bt corn and suggests that at-planting insecticides can be scaled back without yield loss. However, replication years are needed to determine the consistency of these results.

            Ear pests were present at all locations in both hybrids. Because of their window of activity, we would not expect at-planting treatments to affect ear pests, and this was the case. The similar rates of damage between hybrids were likely due to widespread corn earworm resistance to Bt traits and concurrent regional suppression of European corn borer. However, differences in genetic background and phenology between the hybrids prevent comparisons.

            Finally, end of season stand did not differ between treatments. This was consistent with the non-Bt seedling stand, but different from stand for the Bt hybrid. This suggests that the stand gains from Poncho 250 were too small, variable, or short-lived to persist to the end of the season. This supports the conclusion that, given pest pressure across Maryland in 2020, prophylactic insecticides did not increase stand, pest control, or yield.

Participation Summary

Education & Outreach Activities and Participation Summary

2 Webinars / talks / presentations

Participation Summary

20 Farmers
20 Number of agricultural educator or service providers reached through education and outreach activities
Education/outreach description:

The results from this project will benefit Mid-Atlantic grain growers, extension specialists, and researchers by enabling informed decision-making. Currently, growers manage early season pests by applying insecticides at-planting that are not necessarily designed for their specific pest complexes. These treatments may be recommended by seed and chemical dealers and it may be unclear what each treatment targets. Our research will give growers regionally-specific, science-based evidence to help choose at-planting insect management products. The results will benefit both growers producing high-input genetically engineered corn hybrids with Bt traits and growers producing low-input non-Bt corn. In order to communicate information with each stakeholder group we will share results through a number of different channels.

Due to Covid-19, many of the usual avenues for communicating this research have not been available. In the absence of field days and growers’ meetings to present at, we plan to focus on virtual events and other ways to do outreach. Currently, we have presented research at the Maryland Grain Producer’s Utilization Board January meeting. We will continue to look for opportunities to virtually present to growers. To reach a wider audience, results from this project will be published in Agronomy News, a popular newsletter published by UMD extension. This free publication reaches a readership of approximately 3,000 and serves as an easy-to-access reference for stakeholders.

Results from this study have been and will continue to be shared with scientific audiences, including researchers and extension specialists, through presentations at scientific conferences such as annual eastern branch meeting of the Entomological Society of America (ESA) and the annual national ESA meeting. In November 2020 we presented preliminary results on pest pressure, stand, and yield in a student research talk at the virtual national ESA meeting. Presenting to scientific audiences allows us to add to the growing body of research on how prophylactic insecticides impact insect pests and non-targets. It also fosters collaboration and innovation with other researchers working on related projects.

Project Outcomes

Project outcomes:

This area will be evaluated at the end of the project. 

Knowledge Gained:

This area will be evaluated at the end of the project. 

Assessment of Project Approach and Areas of Further Study:

This area will be evaluated at the end of the project. 

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.