Hailstones damaged corn and soybean in multiple locations across Iowa on July 11, 2020. Fungicide use after hail injury is sometimes suggested as a way to benefit damaged plants. In order to help determine if fungicide use after hail is beneficial, Iowa State University undertook multiple years of research.
To summarize this research on reproductive stage crops:
Corn. Results from a three-year study suggest pyraclostrobin + metconazole application may not provide yield-increasing plant health benefits when applied after a mid-season (VT and R2) 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. However, if you are applying a fungicide after hail injury to mid-season corn, waiting at least a week to apply the fungicide is more beneficial than an immediate application.
Soybean. Research suggests 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’s hail extension publications include the above information, and can be downloaded for free from the Iowa State University Extension and Outreach Store.
Initial results for hail injury on vegetative stage crops have been summarized previously at ICM News: https://crops.extension.iastate.edu/blog/adam-sisson-alison-robertson-daren-mueller/would-fungicide-benefit-hail-damaged-crops