By Ethan Stoetzer

Widespread hail occurred in Iowa in June, causing damage to many acres of corn and soybeans. Throughout the month, weather patterns were largely unpredictable, dropping hail in some locations, but none in others. These weather patterns are predicted to continue through the summer.

When the initial storms passed through in early June, most corn was in V6 to V8 growth stages, while soybeans were in V1 to V3 growth stages. Currently, corn is V8 to V12 and beyond, while soybeans range from V3 to R1.

Iowa State University field agronomists and plant pathologists have received multiple questions about what to do with corn and soybeans following hailstorms — specifically, regarding using fungicide. 

Applying fungicide after hail
There are a few schools of thought when it comes to applying fungicide to crops after a hail event. It can be argued that crops may be more susceptible to fungal pathogens resulting from increased stress due to the hail injury, or that wounding of crops may allow pathogens to invade plant tissue. Another reason fungicides are considered post-hail is that physiological benefits gained from a fungicide application are thought to help sustain or increase the yield of damaged crops.

WHY APPLY? Fungicide application may not provide yield-increasing benefits after an early-season hail event when risk of foliar disease is low.

In all these cases, it’s important to note that claims by the chemical industry do not state fungicide applications recover yield potential lost due to hail damage. But some claims do suggest that a fungicide application to hail-damaged crops will protect the remaining green tissue and allow plants to maximize yield after sustaining damage.

ISU conducts new trials
To help answer the question of whether fungicide application after a hail event during vegetative crop stages is beneficial, field trials were conducted by ISU researchers. During 2015 and 2016, trials at research farms at Kanawha and Ames were performed using a hail simulation machine and subsequent fungicide application. 

In corn, hail was simulated at roughly V5 and V9, and fungicide (pyraclostrobin plus metconazole) was applied between one and two weeks later as a “post-hail response” or at R1 growth stage. A treatment that had both the post-hail response fungicide and R1 fungicide application was included.

In soybeans, hail was simulated at approximately V5, and fungicide (fluxapyroxad plus pyraclostrobin) was applied approximately seven to 10 days later as a post-hail response. The fungicide was also applied at R3. A treatment including both the post-hail response and an R3 application was included as well in this study. 

Results: No yield increase
Although analysis is ongoing, a preliminary examination of results may indicate that applying a fungicide in both scenarios didn't result in yield-increasing plant health benefits. As expected, plots with hail injury yielded less than non-injured plots.

These data are similar to what ISU previously reported for fungicide applications after a hail event during early grain fill. In general, a fungicide application may not provide yield-increasing benefits after an early-season hail event when risk of foliar diseases is low. Furthermore, it is important to consider how low grain prices increase the number of bushels needed to recover the cost of fungicide application. 

So, what do you do after a hailstorm regarding fungicide application? Best action would to be evaluate the risk of foliar disease, as well as economic advantages and disadvantages before fungicide application.

If you treat, leave an untreated strip in field
If you do plan on making a fungicide application after early-season hail, it may be advantageous to leave an untreated strip in the field to determine if the application was beneficial come harvest — not only in terms of yield, but also economically. This can help to inform any future decisions about fungicide use on your farm after crop injury from hail. 

For more information on using fungicide post hailstorm, ISU researchers have two publications available for free review through ISU Extension: Hail on Corn in Iowa, IPM 78, and Hail on Soybean in Iowa, IPM 79. Both can be ordered from the ISU Extension Store.

Stoetzer is a communications specialist with the ISU Integrated Pest Management program. Contact him at [email protected].