Hail Damage In Corn - What About Fungicides?

This week several severe thunderstorms moved across the province resulting again in significant hail "events". Some of the hardest hit areas occurred in Lambton, Chathm-Kent and Middlesex areas. In a previous CropPest Ontario article (Issue 8 - June 27, 2008) Horst Bohner (OMAFRA soybean specialist) described the impact on hail damage on corn is very dependant on the corn growth stage. Unfortunately, some the fields damaged by hail were in the VT or tassel/pollen shedding stage which is the most prone to hail and other leaf defoliating injury. Refer to Horst's article for Potential Yield Loss (%) in Corn based on Growth Stage and Defoliation.

A number of producers have asked "would a fungicide application help reduce my risk to secondary disease development due to hail damage". We have very little data to determine whether a fungicide application would reduce disease. What we do know is the primary economically important corn leaf diseases (Northern leaf blight, common rust and gray leaf spot) in the province are excellent "pathogens". What makes them very good disease organisms is their ability to infect regardless of whether the corn is wounded or not. Therefore they are not dependent on open wounds to get into the plant and thus it is unlikely to see a increase in these three leaf diseases as a result of hail injury. The one disease which will increase directly from hail injury is common smut but it is not controlled by foliar fungicides.

Common smut incidence increases in fields where the plants have been wounded by not only hail but frost, drought, mechanical injury, detasselling, herbicide injury, insects or sandblasting as well. High levels of nitrogen and manure promote this disease. Common smut overwinters, not only in the soil but in corn residue as well. The spores are spread by wind and rain through splashing. All above-ground plant tissue is susceptible, but infection occurs most often in areas of actively growing tissue.

Greyish smut galls up to 10 cm (4 in.) in diameter develop on the stalks, ears and tassels, while smaller galls often appear on the leaves. The galls initially have a white membrane cover that eventually breaks and releases dark-brown or black powdery spores. On the leaves, galls develop into a hard, dry growth. Smut galls can replace kernels. Unlike common smut, head smut occurs can occur on both the ears or tassels.

One of the few studies looking at disease, fungicide and hail interactions comes from Carl Bradley (Extension Pathologist) with the University of Illinois. In 2007, he conducted a simulated hail-fungicide trial in which corn plants were damaged with a string trimmer just before tasseling to simulate hail damage. As a control some plots were left undamaged. The fungicides Headline, Quadris, and Quilt were applied to the plots and compared to an untreated check. When the data were statistically analyzed, fungicides did not significantly improve yield compared to the untreated check in the "hail-damaged" plots or the nondamaged plots. Carl did find significant differences in yield however between the damaged and undamaged plots. The simulated hail damage alone did decrease yield by approximately 30 bu/A compared to the nondamaged plots.

Results from a simulated hail damages x foliar fungicide trial on corn at Urbana in 2007. (Source Carl Bradley, University of Illinois).