Agronomy

Statewide Fungicide Results Confirm Foliar Fungal Disease Impact

Close up of plant leaf

Iowa State University researchers recently published their annual fungicide trial data for soybeans in 2019, revealing a continued decline in efficiency among the quinone outside inhibitors (QoI) class of fungicides in preventing foliar diseases in soybeans.

These research results confirm Iowa State findings that foliar fungal disease continues to develop resistance to quinone outside inhibitors class of fungicides.

Best Practices:

  • Use a product with multiple modes of action.
  • Selection of disease-resistant cultivars.

The charts below showcase results from the ISU Research Farms. 

Fungicides reliant solely on QoIs had decreased efficacy against both frogeye leafspot and Septoria brown leaf spot, which are the main foliar diseases of concern in Iowa, and did not provide profitable yield increases. Therefore, researchers conclude that unnecessary use of foliar fungicides should be minimized and an integrated method of disease management that does not depend solely on foliar fungicides should be employed. If a fungicide application is deemed necessary, consult a current efficacy chart like the one produced by the Crop Protection Network to select a fungicide that will control the disease of concern.

ISU Fungicide 1
Table 1. Frogeye leaf spot severity (% in upper canopy) in fungicide treatments across the six locations in 2019. Note, all fungicides are premixes except for Quadris. All products were applied at R3 with nonionic surfactant (Induce at 0.3% v/v) unless otherwise noted. NS= Non-significant, CV = Coefficient of variance, LSD = Least significant difference
Fungicide 1
Table 2. Septoria brown leaf spot index (% in lower canopy) recorded on fungicide treatments across the six locations. Note, all fungicides are premixes except for Quadris. All products were applied at R3 with nonionic surfactant (Induce at 0.3% v/v) unless otherwise noted. NS= Non-significant, CV = Coefficient of variance, LSD = Least significant difference