Soybean farmers in South Carolina typically spend between 5 and 20% of their total annual input cost on pesticides. With the unpredictable weather, commodity price, and pest infestations that SC Soybean farmers have experienced over the last decade, timeliness and effectiveness are critical in maximizing overall profits. Because some common soybean insecticide labels do not provide rain fast intervals following application, this research aims to develop recommendations to define the rain-free period to maximize pesticide efficacy and residual control.

• To determine if rainfall timing after insecticide application influences the efficacy of insecticide used in controlling insect pests in soybean by species.

• To determine the optimum rain free period after application needed to maximize control of insects in order to develop a specific product recommendation.

The expected output/deliverables of this research will be shared with soybean growers in South Carolina and throughout the Southeast. Information exchange will be through the use of newsletters, social media (Twitter and Facebook), Extension publications, Clemson Edisto REC Seminar Series, field days, and grower meetings.

Updated April 19, 2021:
Limited progress has been made at this point since soybean has yet to be planted. We anticipate planting mid-May, treatments will then follow and data collection will start. To this point site selection has been made in B-10A under the variable rate lateral. Plot plans have been finalized as well. The field has received burndown herbicide, supplemental fertilizer, and lime. Over the next quarter we plan to plant all soybean, apply insecticide and wash-off treatments, and begin collecting data.

Updated July 15, 2021:
SCSB Quarterly Report

General Information
Principal Investigator(s) Name(s): Michael Plumblee and Jeremy Greene
Organization: Clemson University – Edisto REC
Date: July 15, 2021
Quarter: 2nd

Proposal Information
Title: Evaluation of Soybean Insecticide Wash-off Intervals for Maximizing Pesticide Efficacy
Amount Expended to Date: $3,169.48 (Most of the expenses thus far have been to purchase lime, fertilizer, herbicides, and begin paying a partial stipend of a graduate student)

Progress Assessment
Kyle Smith, the M.S. graduate student working on this project started in May of 2021. Kyle graduated from ABAC in May of 2021. Kyle will be actively working on this project throughout this year and presenting and publishing research results at appropriate outlets.

On-Station Location
A field (B10A) at Edisto REC in Blackville, SC has been selected for this trial. This field is irrigated with overhead irrigation (lateral move like center pivot). As of July 15, 2021, the field has been sprayed with burndown herbicide application and the field has been strip tilled. Soybean was planted on June 25th with Asgrow 69XF0 at 130,000 seed per acre on 38-inch row spacing. PRE and POST emergence herbicides have been applied. Plots consist of 8-row plots so that we can easily spray insecticide with a plot sprayer. An additional field C8A was planted on July 13 with Asgrow 69XF0 at 130,000 seed per acre on 15-inch row spacing to allow for a dense canopy in the late season when pests tend to flair up. When soybean pest populations increase to threshold appropriate insecticide applications will be made, wash-off intervals will be applied, and insects will be sampled and counted.

Key Performance Indicators
Key performance indicators for this study will be determined at the time of insecticide application and wash-off as well as shortly after when insects are collected and counted in the lab. Furthermore, at harvest when soybean yield is collected, any yield difference that is observed due to wash-off treatment will be valuable information. This research will help develop insecticide efficacy recommendations for soybean insecticides where rain events follow quickly after application. Furthermore, this research will allow for a recommendation to be made that maximized yield and pesticide efficiency, so that if a soybean producer sprays a field and gets rainfall at a specific interval following application, the efficacy of the product can be understood and re-spray could be applied if needed. As of now key circumstances impacting this research are continuous rainfall or lack thereof, and continued maintenance of the plots.

Next Steps
Over the next quarter we plan to continue with the management of the soybean crop and implement insecticide/wash-off treatments.

Updated October 16, 2021:
SCSB Quarterly Report

General Information
Principal Investigator(s) Name(s): Michael Plumblee and Jeremy Greene
Organization: Clemson University – Edisto REC
Date: October 15, 2021
Quarter: 3rd

Proposal Information
Title: Evaluation of Soybean Insecticide Wash-off Intervals for Maximizing Pesticide Efficacy
Amount Expended to Date: $5,152.11 (Most of the expenses thus far have been to purchase lime, fertilizer, herbicides, and paying a partial stipend of a graduate student)

Progress Assessment
Kyle Smith, the M.S. graduate student working on this project started in May of 2021. Kyle graduated from ABAC in May of 2021. Kyle will be actively working on this project throughout this year and presenting and publishing research results at appropriate outlets.

On-Station Location
Since the last report, general crop management to the trial has been conducted except for any insecticide sprays going out. Treatment were applied on 9/30/2021. Plots were sprayed with bifenthrin and then washed off at 0-30 minutes, 1-1.5 hours, 3-4 hours, 6-7 hours, and 24 hours after insecticide application. Initial samplings were conducted and counted, later samplings are in process of being counted and data entered the computer. From initial visual observations there appears to be differences between the number of insects from plot to plot, whether this is due to wash-off interval or with or without insecticide will be revealed once data has been entered and analyzed.

Key Performance Indicators
Key performance indicators for this study will be determined at the time of insecticide application and wash-off as well as shortly after when insects are collected and counted in the lab. Furthermore, at harvest when soybean yield is collected, any yield difference that is observed due to wash-off treatment will be valuable information. This research will help develop insecticide efficacy recommendations for soybean insecticides where rain events follow quickly after application. Furthermore, this research will allow for a recommendation to be made that maximized yield and pesticide efficiency, so that if a soybean producer sprays a field and gets rainfall at a specific interval following application, the efficacy of the product can be understood and re-spray could be applied if needed. As of now key circumstances impacting this research are continuous rainfall or lack thereof, and continued maintenance of the plots.

Next Steps
Over the next quarter we plan to finish sampling for insects based on wash-off treatment that was applied and to harvest all soybean plots. After harvest we plan to begin the data analysis portion of this project and present the findings at local and regional meetings.

Updated December 16, 2021:
SCSB Quarterly Report

General Information
Principal Investigator(s) Name(s): Michael Plumblee and Jeremy Greene
Organization: Clemson University – Edisto REC
Date: December 15, 2021
Quarter: 4th

Proposal Information
Title: Evaluation of Soybean Insecticide Wash-off Intervals for Maximizing Pesticide Efficacy
Amount Expended to Date: $6,177.75 (Most of the expenses thus far have been to purchase lime, fertilizer, herbicides, and paying a partial stipend of a graduate student)

Progress Assessment
Kyle Smith, the M.S. graduate student working on this project started in May of 2021. Kyle graduated from ABAC in May of 2021. Kyle will be actively working on this project throughout this year and presenting and publishing research results at appropriate outlets.

On-Station Location
Since the 3rd quarter report, all soybean has been harvested and data entry has been completed. Preliminary results have been evaluated where all insects caught in the sweep net during each sampling were evaluated against each treatment. From these results, we concluded that bifenthrin at the 6.4 oz/ac rate did very well at controlling and killing all insects. At the 1 DAA and 14 DAA sample timings, there were no significant differences among treatments where the insecticide was sprayed and washed off. At the 7 DAA sampling timing, there was a slight upward trend at the 0-30 minute wash-off timing. From these results, farmers can expect good control of insects even if a light rainfall event occurs after spraying. No significant differences were observed in terms of grain yield regardless of treatment. This may be due to the insects reaching high levels so late in the growing season. Further analysis on a by-species basis is currently being evaluated by graduate student Kyle Smith. This research was recently presented at both the Annual Corn and Soybean Growers Meeting held in Santee, SC on December 8th and at the SC CCA Workshop.

Key Performance Indicators
Key performance indicators for this study will be determined at the time of insecticide application and wash-off as well as shortly after when insects are collected and counted in the lab. Furthermore, at harvest when soybean yield is collected, any yield difference that is observed due to wash-off treatment will be valuable information. This research will help develop insecticide efficacy recommendations for soybean insecticides where rain events follow quickly after application. Furthermore, this research will allow for a recommendation to be made that maximized yield and pesticide efficiency, so that if a soybean producer sprays a field and gets rainfall at a specific interval following application, the efficacy of the product can be understood and re-spray could be applied if needed.


Next Steps
Over the next quarter we plan to continue and finish all data analysis and generate a final report with those results for the SC Soybean Board and SC Soybean Producers. We also plan on presenting these findings at local and regional meetings throughout the winter meeting season.

Updated January 17, 2022:
SC Soybean Board Final Report

General Information
Principal Investigator(s) Name(s): Michael Plumblee and Jeremy Greene
Organization: Clemson University
Date: 1/17/2022
Quarter: Final

Proposal Information
Title: Evaluation of Soybean Insecticide Wash-off Intervals for Maximizing Pesticide Efficacy
Amount Expended to Date: $8,149

Project Summary
Soybean farmers in South Carolina typically spend between 5 and 20% of their total annual input cost on pesticides. With the unpredictable weather, commodity price, and pest infestations that SC Soybean farmers have experienced over the last decade, timeliness and effectiveness are critical in maximizing overall profits. Because some common soybean insecticide labels do not provide rain fast intervals following application, this research aims to develop recommendations to define the rain-free period to maximize pesticide efficacy and residual control.
Treatments consisted of Bifenthrin (Brigade 2EC) being sprayed at a full rate of 6.4 oz/acre. Simulated rainfall (irrigation) was then applied to specific plots immediately following application to 30 minutes, 1-1.5 hours, 3-4 hours, 6-7 hours, and 24 hours after application. An untreated control was included for comparison purposes as well as plots receiving no simulated rainfall for at least 24 hours. The insect species that were counted include kudzu bug, three-cornered alfalfa hopper, stink bugs, soybean looper, velvet bean caterpillar, grasshoppers, and others. Sweep net sampling was conducted prior to and after pesticide applications are made to monitor control.
Stinkbugs:
Soybean plots were swept with a sweep net at various intervals after insecticide and wash-off treatments were applied, all insects caught in the sweep net were counted in the lab. Since stinkbug is a common pest that soybean farmers deal with each year, we analyzed the results based on stinkbug in this portion of the trial. From these results we observed significant differences between treatments at each sampling timing, however, the most significant impact was a result of where Bifenthrin was applied and where it was not. (Figures 1, 2, and 3). Among the insecticide-treated plots control remained similar regardless of when the insecticide was washed off after application. Furthermore, water applied alone (0.3” of simulated rainfall per plot) did not impact stinkbug populations. Based on these results, we can conclude that in 2021 we achieved excellent stinkbug control even when simulated rainfall was applied immediately following a Bifenthrin application, allowing pesticide applicators more flexibility when applying these products and better understanding their efficacy if a rain event should follow. We did note that stinkbug populations in this trial did not build to threshold levels until very late in the growing season, due to the insects moving into the soybeans so late, yield results may vary in a year where stinkbug pressure occurs earlier in the season.
Other Insects:
Additionally, several other insects were evaluated in this trial to determine if product efficacy was reduced due to wash-off intervals. When analyzing all caterpillar pests that were caught in the sampling nets, no significant differences were observed among all treatments both sprayed and untreated with insecticide. Again, we hypothesize that this was a result of low pest populations in the field. Kudzu bugs were also analyzed and displayed a similar result to the caterpillar pests where no differences in kudzu bug numbers were revealed regardless of treatment.
Yield:
Ultimately, without seeing drastic differences in insect numbers from the sampling timings we hypothesized that significant yield differences would also be unlikely. Upon harvest, we confirmed our hypothesis that no significant yield differences were observed in this trial among treatments regardless of wash-off interval timing or whether an insecticide was applied or not. (See Figure 4). Plots that never received an insecticide application season-long still resulted in a soybean yield of 50 to 60 bushels/acre.

Key Performance Indicators
The KPIs for this research helped determine if specific soybean insecticides have reduced efficacy on control soybean pests when exposed to different simulated rainfall events at the field scale. These results could alter how soybean farmers apply pesticides to ensure that they maximize efficacy and profitability reducing the likelihood of having a product failure. The key performance indicator will be to define the simulated rainfall interval in which pesticide efficacy was not altered for soybean pesticides. From our results, we determined that in 2021, wash-off intervals did not influence product efficacy among stinkbugs, lepidopteran pests, or kudzu bugs. Challenges that were faced in this research that could have influenced the KPIs measured would have been the overall pest pressure in the natural landscape where the trial was conducted, resulting in non-yield limiting pest populations.

Next Steps
The next steps of this project would be to evaluate wash-off intervals among insecticides within a year where pest pressure is yield-limiting and occurs earlier in the growing season. From there, we aim to publish these results in an Extension report/bulletin, on the new SC Crops Blog and begin sharing with soybean growers across the region at local, regional, and national meetings. This research has already been presented at the 2021 SC Corn and Soybean Grower’s Meeting held in Santee, SC on Dec. 8th, 2021.

View uploaded report

Soybean farmers in South Carolina typically spend between 5 and 20% of their total annual input cost on pesticides. With the unpredictable weather, commodity price, and pest infestations that SC Soybean farmers have experienced over the last decade, timeliness and effectiveness are critical in maximizing overall profits. Because some common soybean insecticide labels do not provide rain fast intervals following application, this research aims to develop recommendations to define the rain-free period to maximize pesticide efficacy and residual control.
Treatments consisted of Bifenthrin (Brigade 2EC) being sprayed at a full rate of 6.4 oz/acre. Simulated rainfall (irrigation) was then applied to specific plots immediately following application to 30 minutes, 1-1.5 hours, 3-4 hours, 6-7 hours, and 24 hours after application. An untreated control was included for comparison purposes as well as plots receiving no simulated rainfall for at least 24 hours. The insect species that were counted include kudzu bug, three-cornered alfalfa hopper, stink bugs, soybean looper, velvet bean caterpillar, grasshoppers, and others. Sweep net sampling was conducted prior to and after pesticide applications are made to monitor control.
Soybean plots were swept with a sweep net at various intervals after insecticide and wash-off treatments were applied, all insects caught in the sweep net were counted in the lab. Since stinkbug is a common pest that soybean farmers deal with each year, we analyzed the results based on stinkbug in this portion of the trial. From these results we observed significant differences between treatments at each sampling timing, however, the most significant impact was a result of where Bifenthrin was applied and where it was not. (Figures 1, 2, and 3). Among the insecticide-treated plots control remained similar regardless of when the insecticide was washed off after application. Furthermore, water applied alone (0.3” of simulated rainfall per plot) did not impact stinkbug populations. Based on these results, we can conclude that in 2021 we achieved excellent stinkbug control even when simulated rainfall was applied immediately following a Bifenthrin application, allowing pesticide applicators more flexibility when applying these products and better understanding their efficacy if a rain event should follow. We did note that stinkbug populations in this trial did not build to threshold levels until very late in the growing season, due to the insects moving into the soybeans so late, yield results may vary in a year where stinkbug pressure occurs earlier in the season.
Additionally, several other insects were evaluated in this trial to determine if product efficacy was reduced due to wash-off intervals. When analyzing all caterpillar pests that were caught in the sampling nets, no significant differences were observed among all treatments both sprayed and untreated with insecticide. Again, we hypothesize that this was a result of low pest populations in the field. Kudzu bugs were also analyzed and displayed a similar result to the caterpillar pests where no differences in kudzu bug numbers were revealed regardless of treatment.
Ultimately, without seeing drastic differences in insect numbers from the sampling timings we hypothesized that significant yield differences would also be unlikely. Upon harvest, we confirmed our hypothesis that no significant yield differences were observed in this trial among treatments regardless of wash-off interval timing or whether an insecticide was applied or not. (See Figure 4). Plots that never received an insecticide application season-long still resulted in a soybean yield of 50 to 60 bushels/acre.