Hailstones damaged corn and soybean crops in multiple locations across Iowa on July 11. Fungicide use after hail injury is sometimes suggested as a way to benefit damaged plants. To help determine if fungicide use after hail is beneficial, Iowa State University crop disease specialists undertook multiple years of research.
Here’s a summary of the results, provided by Adam Sisson, ISU Extension pest management specialist. ISU Extension plant pathologists Daren Mueller and Alison Robertson also assisted with this research, which pertains to the use of fungicides when the hail hits during the reproductive stage of the crops.
For corn, results from a three-year study suggest a pyraclostrobin plus metconazole application may not provide yield-increasing plant health benefits when applied after a midseason (VT and R2 growth stage) hail event when foliar diseases are not present at damaging levels. Results from this study support the claim that economic profitability from fungicide use in corn is more likely if fungicide application is for the purpose of disease management when disease risk is high.
What if you’ve decided to go ahead and apply the planned fungicide application? How long should you wait after the hail has hit the crop in the field? The ISU specialists say if you are applying a fungicide after hail injury to midseason corn, waiting at least a week to apply the fungicide is more beneficial than an immediate application.
The research results suggest that hail injury at soybean growth stage R1 should not, by itself, be reason enough to make an application of foliar fungicide at R3 when disease risk is low.
Iowa State University Extension publications on managing hail-damaged crops include more of this information for corn and soybeans. The publications can be downloaded for free from the ISU Extension and Outreach Store.
Initial results of the study for help in evaluating hail injury on the vegetative stage of crops have been summarized on the ISU ICM website.