Fungicide use in soybean production
Two of the myriad things that are certain in soybean farming are 1) getting an adequate stand is the first step that must be achieved to have a successful crop, and 2) dockage at the elevator resulting from poor seed quality can significantly lower the economic value of even an exceptionally high seed yield. The following articles highlight results from research that was conducted to address these two issues.
An article titled “Soybean stand and yield impact from a fungicide seed treatment in North Carolina soybean production” from North Carolina State Univ. provides the following information.
• Studies were conducted for 2 years at 18 locations in North Carolina.
• Either Asgrow AG56X8 [RM 5.6] or AG59X9 [RM 5.9] RR2X varieties were used in both years.
• Treatments were 1) planted seed treated with a fungicide vs. 2) untreated planted seed. The fungicide used was Vibrance Trio that contains fludioxonil [Group 12], sedaxane [Group 7], and mefenoxam [Group 4] fungicides that target common seedling diseases [Pythium spp., Rhizoctonia solani, Phytophthora sojae, Fusarium spp.] of soybean.
• Of the 18 locations in the study, 1 was planted before April 20, 4 were planted from Apr. 23-Apr. 30, and 5 were planted from May 3 through May 6.
• Soybean stand between growth stages V1 and V3, and seed yield were measured.
• Seven of the 18 locations showed significant stand protection when the seed treatment was used. The authors indicated that lower soil temperatures and greater rainfall were likely involved in stand protection. Overall, the fungicide seed treatment used in this research provided average stand protection of 9187 plants/acre, or 9%.
• Seed treatment resulted in an average seed yield increase of only 1.3 bu/acre, which was likely inconsequential.
• These results confirm the following. 1) Fungicide seed treatment can significantly protect soybean stand by about 10% in environments where fungal pathogens are present that may promote reductions in germination and seedling emergence. 2) Fungicide-treated soybean seed should not be planted with an expectation of a resulting significant yield increase.
The above research results confirm what has long been promoted for ESPS plantings in the Midsouth–i.e. a fungicide seed treatment should be used to ensure stand protection and to allow for about a 10% reduction in seeding rate, but not to increase soybean seed yield.
An article titled “Influence of fungicide on soybean seed quality from delayed harvest and environment” from Louisiana State Univ. provides the following.
• Midsouth soybean producers often use late-season applications of foliar fungicides to prevent soybean seed deterioration that can occur as a result of inclement weather events that often occur in the region at harvest time.
• Experiments were conducted in Louisiana in 2019 and 2020 to evaluate the effect of fungicide applications made to mitigate detrimental environmental effects on seed at optimum harvest time [~13% seed moisture], or following delayed harvest.
• A MG IV soybean variety was planted in early May and a multiple-mode-of-action fungicide [either Miravis Top or Revytek] was applied at about stage R6.5 to compare the effect of the fungicide on seed quality vs. the effect of not applying a fungicide.
• In field experiments, harvest delays of approximately 20, 30, and 44 days after optimum harvest time were used to test the effect of the fungicide applications on seed quality maintenance when harvest is delayed as a result of inclement weather. In growth chamber studies, mature pods from plants that had been treated with the above fungicides were exposed to 100% relative humidity for 48 and 96 hours.
• In both years and in both the field and chamber studies, application of the above fungicides had no significant effect on seed quality when harvest occurred optimally or after the indicated delays.
• Overall, the results from this research indicate that the application of foliar fungicide should not be expected to mitigate the causes of poor soybean seed quality that often occurs because of weather-delayed harvest in this region.
Results provided in the above articles reaffirm that 1) applying a fungicide treatment to soybean planting seed is a wise agronomic input, and 2) a genetic solution will likely be required to mitigate the quality problem that often occurs in seed harvested from ESPS plantings in the Midsouth.
Composed by Larry G. Heatherly, Jan. 2025, larryh91746@gmail.com