Wind and storm damaged soybean have been reported across Iowa, creating yet another stress for farmers this growing season. Certain fungicide products are marketed as being capable of reducing stress in crops, so should they be sprayed on soybean this late in the season?
Fungicide response to damaged crops
While we do not have data following extremely strong winds, we can tease apart the damage to crops and look at a few tidbits of information to help come to an answer. First, we can revisit some of the data from an Iowa State University research project investigating fungicide use on hail-damaged soybeans over multiple years. In general, 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. You can find more information here: Hail on Soybean in Iowa (IPM 0079) at https://store.extension.iastate.edu/product/14792
Disease risks associated with hail damage
It is important to remember that a fungicide application cannot recover yield potential lost due to storm damage. Fungicides protect yield potential by reducing disease. There are some diseases of soybean that are favored by wounding, e.g., bacterial blight and bacterial pustule. But fungicides are not effective against the pathogens that cause these diseases. The foliar diseases that are managed by fungicides (e.g., brown spot and frogeye leaf spot) are caused by pathogens that do not require wounds for infection. These foliar diseases will influence the yield response to fungicides more so than hail damage. In general, we have seen very low levels of brown spot and frogeye leaf spot across Iowa prior to the storm, so we do not anticipate there being fields that are overrun by these diseases after the storm.
Late season restrictions to fungicide
As with any pesticide application late in the season, there may be harvest restrictions. You can find these restrictions on the Crop Protection Network fungicide efficacy publication.