Project Details:

Optimizing fungicide spray volume for improved white mold management in soybeans

Parent Project: This is the first year of this project.
Checkoff Organization:North Dakota Soybean Council
Categories:Agronomy, Soybean diseases
Organization Project Code:NDSC 2023 Agr 13
Project Year:2023
Lead Principal Investigator:Michael Wunsch (North Dakota State University)
Co-Principal Investigators:

Contributing Organizations

Funding Institutions

Information and Results

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Project Summary

This project seeks to quantify the impact of fungicide spray volume on white mold management in soybeans with the goal of minimizing application costs and maximizing the profitability of fungicides for management of white mold in soybeans. The use of fungicide spray volumes greater than 10 gal/ac is a widely recommended strategy for improving fungicide performance against white mold in soybeans. Research supporting that recommendation had been lacking, and recent findings suggest that increasing spray volume above 10 gal/ac may have little or no effect on white mold management. In research conducted in Brazil, increasing fungicide spray volume from 10.7 to 21.4 gal/ac had no impact on white mold management with either the fungicide Omega (registered in the U.S.) or the fungicide procymidone (not registered in the U.S.). In research conducted in North Dakota in 2020 with the fungicide Endura, increasing fungicide spray volume from 10 to 25 gal/ac had no impact on white mold management or yield in pinto, black, dark-red kidney, light-red kidney, or navy beans. This project seeks to identify the minimum spray volume needed to optimize fungicide performance for white mold management in soybeans. Field studies will be established under irrigation in Carrington and Oakes, ND to assess white mold control, yield response, and profitability of applying fungicides at 5, 7.5, 10, 12.5, and 15 gal/ac. Testing will be conducted on varieties differing in architecture (upright versus bushy) with each of two widely utilized fungicides, Endura (at 5.5 oz/ac) and ProPulse (at 6 fl oz/ac).

Project Objectives

1. Identify the minimum fungicide spray volume needed to maximize white mold control and soybean yield and quality
2. Evaluate whether the impact of fungicide spray volume on white mold management differs across fungicides
3. Quantify the impact of soybean architecture (bushy versus upright) on the optimum fungicide spray volume for white mold management

Project Deliverables

1. Development of rigorous recommendations on the fungicide spray volume that optimizes white mold management, soybean yield, and soybean profitability under white mold pressure.
2. Dissemination of results to North Dakota soybean growers, crop advisors, and extension personnel

Progress of Work

Updated December 1, 2022:
Changes to the study objectives:
Objective #2 was changed to the following: Evaluate whether the impact of fungicide spray volume on white mold management differs for a single fungicide application versus two sequential applications.
This change was discussed during the grant defense in December 2021. Two fungicide applications are often needed in irrigated soybeans, and soybean canopy characteristics differ between the first and second applications: Soybeans are taller, and the canopy is denser at the second application. Because of the differences in canopy characteristics, there was concern that the impact of spray volume may differ for a single versus two sequential applications.
Completed work:
Soybeans were planted on June 2 and 3 in Carrington and on June 3 in Oakes. The relatively late planting date was due to the cold, wet spring. Because of concerns about delayed canopy closure associated with the relatively late planting date, soybeans were seeded to narrow (14-inch) rows. The experiments were established as a randomized complete block design with a split-plot arrangement, with the number of fungicide applications (one versus two) as the main factor and fungicide spray volume as the sub-factor. The study in Carrington was conducted with 9 replicates, and the study in Oakes was conducted with 6 replicates. White mold disease pressure is often highly variable over short distances, and a large number of experimental replicates was utilized to maximize the likelihood of each treatment being evaluated the same number of times in areas of high versus low disease pressure. Treatment plots were 25 feet long and 5 feet wide (consisting of four rows centered within the 5-foot width). To facilitate overspray of treatments and capture any fungicide drift, treatment plots were separated by 5-foot wide non-harvested filler plots on one side and 10-foot wide non-harvested filler plots on the other side. A tractor with a 5-foot wheelbase was used to apply fungicide treatments, and this tractor was driven in the center of the 10-foot wide filler plots. Parallel studies were established with each of four different soybean varieties in Carrington and three different varieties in Oakes. The number of varieties assessed in Oakes represents an increase from the two varieties proposed in the original grant. Testing was conducted on the following varieties in Carrington: Xitavo ‘XO0602E’ (0.6 maturity), Asgrow ‘AG06X8’ (0.6 maturity), Xitavo ‘XO0731E’ (0.7 maturity), and Asgrow ‘AG09Xf0’ (0.9 maturity). Testing was conducted on the following varieties in Oakes: Xitavo ‘XO1041E’, Asgrow ‘AG11X8’, and Xitavo ‘XO1212E’. The Asgrow varieties were Extend-type soybeans, and the Xitavo varieties were Enlist-type soybeans. Fertility and weed management were conducted in accordance with best practices. In Carrington, fungicides were applied July 25 at the early R2 growth stage (79 to 91% of plants at the R2 growth stage, depending on the variety) and August 1 at early R3 growth stage. In Oakes, fungicides were applied July 21 at the full R2 growth stage (100% of plants at the R2 growth stage across all three soybean varieties) and on August 1 at the R3 growth stage. Fungicides were applied with a PTO-driven tractor-mounted sprayer equipped with a pulse-width modulation system (Capstan AG, Topeka, KS). Pulse width was modified as needed to maintain a constant driving speed, the same nozzles, and the same application pressure across spray volume treatments, with pulse width manually adjusted and set on the basis of the measured spray output. Nozzles and application pressures were selected to calibrate the droplet size relative to canopy closure, with medium droplets used when the canopy was nearing closure and coarse droplets utilized when the canopy was closed. TeeJet (Spraying Sytems Co.; Wheaton, IL) extended-range flat-fan nozzles were utilized due to their broad commercial usage and the familiarity of North Dakota producers with these nozzles. Fungicide application details are presented in Table 1. In Carrington, supplemental irrigation was applied via low-output rotating micro-sprinklers with a 20-foot spray radius established in a 20-foot offset grid pattern. Irrigation commenced at late vegetative growth and continued through the R5 growth stage, with irrigation delivered as needed to maintain the top half-inch of the soil moist (to facilitate production of apothecia and spores by the Sclerotinia pathogen) beginning at late vegetative growth and as needed to create conditions favor. In Oakes, supplemental overhead irrigation was applied via a linear irrigator as needed to optimize soybean agronomic performance. White mold was assessed on October 13-14 in Carrington and October 20-21 in Oakes when soybeans were at maturity. All plants in the third row (counted from the side of the plot closest to the tractor driving pass) of each four-row plot were individually assessed for white mold severity on a 0 to 5 scale representing the percentage of the plant impacted by Sclerotinia stem rot: 0 = 0%, 1 = 1-25%, 2 = 26-50%, 3 = 51-75%, 4 = 76-99%, 5 = 100%. Soybeans were harvested October 13-14 in Carrington and October 21 in Oakes.
Preliminary results:
Increasing fungicide spray volume from 5.0 to 15.0 gal/ac had very little impact on white mold management across the seven soybean varieties tested. Response to fungicide spray volume was similar across upright varieties with delayed canopy closure, bushy varieties with early canopy closure, tall varieties and short varieties (Figures 1, 3). When a single fungicide application was made, no impact on white mold severity or soybean yield was observed as fungicide spray volume increased from 5.0 to 15.0 gal/ac (Figures 1, 2). When two sequential fungicide applications were made 9 or 11 days apart, a weak trend of slightly improved disease control and increased yield was observed as spray volume increased from 5.0 to 15.0 gal/ac (Figures 3, 4), but statistical separation across spray volume treatments was only observed for the disease reduction conferred by 5.0 vs. 12.5 gal/ac (Figure 4).
The split-plot experimental design allowed for a statistical assessment of whether the response to fungicide spray volume was consistent or whether it changed when a single fungicide application was made versus two sequential fungicide applications. No statistically significant differences (at a 95% level of confidence) in the impact of increased spray volume on yield were observed across one versus two fungicide applications. Statistically significant differences (P < 0.05) in the impact of increased spray volume on white mold control were observed for two of seven varieties. In both varieties, increased fungicide spray volume had a greater impact on disease control when fungicides were applied twice (versus a single application).
Work to be completed: Plot-level seed quality and soybean market grade assessments are in progress and will be completed by January 2023. A user-friendly summary of results will be posted to the NDSU Carrington webpage by March 2023. Major results will be disseminated to stakeholders at winter crop meetings and summer plot tours from January to September 2023.

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Final Project Results

Benefit to Soybean Farmers

This project will improve the profitability of soybean production in fields where Sclerotinia is a problem by identifying profit-maximizing strategies to improve soybean agronomic performance and profitability under white mold disease pressure.

Performance Metrics

Project Years