Update:
This year (2023) we replicated our study measuring timing, abundance, and economic impact of slugs, insects, and early-season pathogens when full season soybean planting date varies. We also assessed the impact of planting date on the control efficacy and economic benefits of adding a pyrethroid insecticide to the post-emergence herbicide application. In 2022, economic pest damage did not occur and there was no difference in yield between planting dates or pesticide treatments. However, weather and pest populations can vary greatly from year to year, so we are repeating this experiment.
Methods
As in 2022, the two planting date treatments [as early as possible (May) and one month later (June)] and two pesticide (postemergence herbicide only and insecticide+herbicide) treatments were replicated three times per field in two fields at each of two farms [CMREC (Beltsville, MD) and WyeREC (Queenstown, MD)], for a total of 6 plots per treatment combination (date*pesticide) per farm. We planted P38A54E full season, non irrigated soybeans at 15” row spacing for a population of 140,000 live seeds per acre. In 2022, the planting populations were slightly different across the farms (WyeREC was 120,000, CMREC was 140,000), and WyeREC used a planter while CMREC used a drill. This year, both farms used a drill and the planting population was the same. The earlier planting treatment (May) went in on 4/27 at WyeREC and 5/12 at CMREC. The later planting (June) went in on 5/31 at WyeREC and 6/12 at CMREC. The highest labeled rate of Warrior II (1.92 fl oz/acre) was applied to the insecticide+herbicide treated plots on 7/4 (CMREC) and 7/11 (WyeREC) for the May plots and to 7/20 (CMREC) and 7/25 (WyeREC) for the June plots. This is the rate recommended for grasshoppers, stink bugs and spider mites, which were identified by Maryland Soybean Board in 2021 as key pests of soybean. To evaluate the pest control benefits of the post-emergence Warrior II application, we focused our most intensive pest sampling efforts on the dates immediately before spraying and about 2 weeks after spraying in both 2022 and 2023. In addition, we use multiple approaches to measure pest activity and damage throughout the season.
Specifically, we use monitoring traps to evaluate pest and beneficial abundance on a weekly basis, take snapshot visual and sweep net assessments of arthropod activity, and periodically quantify the number of plants damaged and damage incidence. Since planting, we have monitored slug activity using 2 roof shingle traps (with a cup of soapy water underneath) per plot. Slug activity has tapered off, and next week we will remove all remaining slug traps (6 weeks after the second planting date). For the duration of the season, we check moth traps for fall armyworm, western bean cutworm, and corn earworm weekly. From the early vegetative stages until canopy closure, we do visual assessments of 6ft of row (both sides) recording insect activity/abundance, and deploy 2 sticky cards per plot weekly. We also started sweep netting (10 sweeps of a single row) every other week when the plots reached V4 and plan to continue through September.
By using a range of sampling techniques, we are able to capture a more complete image of the pest and beneficial community in Maryland full season soybean. In addition to insect counts, we also measure the number of plants damaged by counting stand, the number of plants with more than 0.25sqcm feeding damage, and the number of plants with yellowing, wilting, necrosis, or any other obvious disease symptoms in our visual assessments. To measure damage severity, we quantify leaf defoliation by sampling the unifoliate leaves when the plants are in VC-V2 and the top 2 trifoliates in later stages. Until V4 or later, we estimate leaf area removed and total leaf area non-destructively using a 1x1cm2 grid on a transparent acrylic sheet. After V4, we remove 5 representative damaged leaflets from different plants at each sampling site, which is then analyzed using the LeafByte app for a more accurate measure of % leaf area removed. Sweep nets and defoliation are the most commonly used metrics for determining economic levels of pest pressure in soybeans; therefore, we also compare these results to established economic thresholds.
We have several major pest sampling events remaining in the growing season. We will be completing our “post-spray” sample for the June plantings next week (7/31-8/3) at both farms. When the first June plants start reaching R6, we plan to count the number of total and damaged pods on 3 plants and destructively sample 2 representative soybean plants from three different sampling sites distributed in a diagonal transect across each 45 by 60 ft subplot. Last year this fell near the last week of August. We will record the number of immature and mature pods on the collected plants as well as any signs of disease or insect feeding. At harvest we plan to repeat our 2022 measurements of Dectes stem borer infestation (# of lodged plants), seed damage (stink bug and pathogen), seed quality (% undamaged), and yield, to compare both planting dates and insecticide treatments in terms of economic benefit. In addition to these pest and damage measurements we evaluate plant growth stage, height, and width (until canopy closure).
Results
Slug numbers were generally lower this year than last year, but slug damage was still observed in early season visual assessments. Dry weather has had an observable effect on the beans, particularly in the May plots. Unusually high thrips feeding was visible on early vegetative plants. Deer damage has also been noticeable, although plants are typically able to recover and regrow. At both farms we have detected grasshoppers, crickets, aphids (but not in high densities), spider mites, the occasional caterpillar (mainly species of lower concern like green cloverworm, silver spotted skipper, and yellow striped armyworm) as well as a few spotted cucumber beetles. Bean leaf beetles have been more abundant at the Wye in the last few weeks and were also the most abundant pest found in visual assessments in 2022, but defoliation did not reach thresholds. Beneficials including spiders and minute pirate bugs which prey on spider mites and thrips commonly occur. Leaf defoliation averages that have been analyzed thus far (May-June) are below threshold and between 2-15%, and our sweep net samples (10 sweeps) have often contained zero or very few pest species, although more analysis is needed to confirm that this translates to below threshold. Overall our measurements and observations suggest that pest presence and damage are not near threshold levels in either planting date. In terms of plant growth, the plantings vary more earlier in the season and begin to catch up towards the end of the season. For instance, canopy closure occurred in the May plantings between 7/4 and 7/11 at CMREC and between 7/6 and 7/13 at WyeREC, and in the June plantings between 7/18 and 7/25 at Beltsville and 7/14 and 7/19 at WyeREC. This week, the May plots were in R2 at WyeREC and ranging from V5 to R2 at CMREC and the June plots were between R3-R5 at both farms.
Summary
In terms of work remaining, we have 912 sticky cards in total from 2022 in the freezer to be analyzed and will have a similar number from this year. We started to process the 648 sweep nets collected in 2022 over the previous winter and are continuing to make progress as labor is available but will likely be analyzing our 2022 and 2023 samples well into 2024. Preliminary 2022 results were presented at the 2023 Commodity Classic on 7/27. Overall, we found that there were some differences in pest pressure and its overlap with the post-emergence application between the May and June planting treatments in 2022. The mean number of pests per plot observed in visual assessments was generally higher in the earlier plantings and tended to increase as the season progressed across all treatments. The insecticide does not seem to have a lasting effect on insect presence, but for both May and June plots, there is a consistent and distinct decrease in leaf area consumed in the plots treated with Warrior II when compared to the plots treated with herbicide only. However, leaf area defoliated was well below thresholds (10-40% depending on growth stage and conditions) for all treatments. Planting later (June) yielded a very minor reduction in the percent of damaged seed and a slightly larger reduction in the percent of damaged pods, although pod damage was below the management threshold (5%) for all treatments. We found that planting a month earlier did not produce a yield benefit and that tank mixing Warrior II similarly did not improve yield, regardless of planting date. We look forward to analyzing our 2022 and 2023 results over the winter and submitting our final reports to the MSB in spring 2024.
Update:
Background
This past year (2023) we replicated our study measuring timing, abundance, and economic impact of slugs, insects, and early-season pathogens across two planting dates (as early as possible and one month later) and two farms [CMREC (Beltsville, MD) and WyeREC (Queenstown, MD)]. We also assessed the impact of planting date on the control efficacy and economic benefits of adding a pyrethroid insecticide to the post-emergence herbicide application. The experimental design was replicated in two fields at each farm with three replicates of each treatment combination (date*pesticide) per field. In 2022, we found no significant differences in yield or seed quality between post-emergence herbicide alone and post-emergence herbicide mixed with Warrior II across both planting dates, but as weather and pest populations can vary greatly from year to year, we repeated this experiment in 2023 to make our conclusions about whether or not there is a pest control benefit more robust.
Experimental Design
For this experiment, we planted P38A54E full season, non irrigated soybeans at 15” row spacing for a population of 120-140,000 live seeds per acre using a planter or a drill, with 6-8 rows skipped to provide 30” rows to install traps (Figure 1). Plots were 45 ft wide by 60-79 ft long. We aimed to plant the earlier planting treatment (May) as soon as possible and the later planting treatment (June) 1 month later. We followed standard nutrient and chemical management practices for mid Atlantic no till, with burn down, pre-emergence, and post-emergence herbicide treatments. When we applied the post-emergence herbicide, we mixed in the highest labeled rate of Warrior II (1.92 fl oz/acre) for the insecticide+herbicide treated plots. This is the rate recommended for grasshoppers, stink bugs and spider mites, which were identified by MSB in 2021 as key pests of Maryland soybean. To evaluate the pest control benefits of the post-emergence Warrior II application, we focused our most intensive sampling efforts (sweep netting, defoliation assessments and visual counts of insects and damaged plants) on the dates immediately before spraying and about 2 weeks after spraying in both 2022 and 2023. This will allow us to compare the insecticide sprayed plots to the herbicide only plots to determine if there was an effect.
Sampling Methods
As in 2022, we used multiple methods in 2023 to track pest presence and damage as well as measure the overall diversity and abundance of the invertebrate community. For the duration of the season, we checked moth traps for fall armyworm, western bean cutworm, and corn earworm weekly. For the first 11 weeks after planting, we monitored slug activity using 2 roof shingle traps (with a cup of soapy water underneath) per plot. From the early vegetative stages until canopy closure, we conducted 3 visual assessments of 6ft of row (both sides) and deployed 2 sticky cards in each plot to record insect activity/abundance. We also used sweep nets (10 sweeps of a single row in 3 locations) to sample (See Figure 1 for sampling locations.)
In addition to insect counts, in our visual assessments we also counted total stand, the number of plants with insect damage (damage incidence), and the number of plants with yellowing, wilting, necrosis, or any other obvious disease symptoms. Disease symptoms were photographed and leaf samples taken for analysis by a UMD plant pathologist. When plants were either located outside plot area or were not going to survive until harvest, they were dug up with the roots for better identification. We also quantified plant growth stage, height, and width (until canopy closure) as well as leaf defoliation. Leaf defoliation (in %) captures damage severity, and we sampled the unifoliate leaves when the plants are in VC-V2 and the top 2 trifoliates in later stages, using nondestructive estimation until V4. In 2022, we only estimated the area removed, but in 2023, we estimated both the area removed and the total area in order to be able to accurately calculate % defoliation in our early season nondestructive samples. After V4, we removed 5 representative damaged leaflets from different plants at each sampling site and analyzed leaf defoliation using the LeafByte app which measures total area and the amount removed. In late August, we destructively sampled 2 representative soybean plants per plot and counted the number of total and damaged pods. Prior to harvest we re-evaluated the stand and measured lodging. At harvest we repeated our 2022 measurements of Dectes stem borer (DSB) infestation (# of infested stems), seed damage (stink bug and pathogen), seed quality (% undamaged), and yield, to compare both planting dates and insecticide treatments in terms of economic benefit.
Data progress
Data analysis is ongoing. Sweepnets and sticky cards, after being collected in the field, were stored in plastic bags and frozen. All identification of 2022 and 2023 sweepnet samples was recently completed, and all data has been prepared for analysis. Preliminary 2022 results for defoliation, yield, and pod damage were presented at the 2023 Commodity Classic on 7/27/23, and a more summarized and final version of this data was presented at the 2023 Entomological Society of America National Meeting on 11/6/23. The 2023 yield measurements were completed the day of harvest, and the stems collected during harvest were analyzed for DSB in the days following. Seed quality and damage measurements were recently completed for 2023. We still have 912 sticky cards from 2022 and 792 sticky cards from 2023, corresponding to 11 weeks of measurement at CMREC and 12 weeks at WyeREC, and arthropod identifications for these have just begun.
Results/Summary
In 2022, we found no significant differences in yield as a result of planting date (F1,44 = 0.0737, p = 0.787) or treatment (F1,44 = 0.0142, p = 0.906), using a mixed linear effect model with farm included in the model as a random effect. In 2023, planting date had more of an impact on yield, particularly at one of the farms (CMREC, in Beltsville, MD), with the later plantings yielding lower. When analyzed with the mixed effect linear model, treating farm as a random effect, we did find a significant relationship between planting date and yield (F1,44 = 5.12, p = 0.0286), but no relationship with treatment (F1,44 = 0.245, p = 0.623).
In 2022, only planting date (F1,137 = 8.44, p = 0.00428) had an effect on mean leaf area defoliated over the measurement period. Insecticide treatment (F1,156 = 3.12, p = 0.0794) had no effect in a mixed linear model with farm as a random effect and date as a nested random effect. Mean leaf area defoliated was lower in the later planting, but defoliation treatment thresholds are around 15-20% for the reproductive stages and higher for the vegetative stages. The percent of leaf defoliation measured even during the reproductive stages did not exceed 12% and was usually lower, so there was not an economic level of defoliation.
In 2023, there was no difference between mean leaf area defoliated as a result of either planting date (F1,183 = 0.044, p = 0.947) or insecticide treatment (F1,178 = 0.0870, p = 0.768). A similar result was found for percent area defoliated when compared by planting date (F1,182 = 3.54, p = 0.0613) and insecticide treatment (F1,178 = 0.0365, p = 0.849). Mean percent of leaf defoliation measured (by date) did not exceed 15% once plants passed R1. Leaf defoliation greater than 15% was only found in June 12 plots at Beltsville in the VC-V1 stages.
View uploaded report 