Gray leaf spot, the primary foliar disease in Kentucky corn, has progressed very little in the past several weeks in our research trial at Spindletop Farm in Fayette County.

In the fields I have been in this summer, the activity of the disease varies quite a bit (depending on hybrid, rotation practices, tillage, planting date, and other factors). While there are definitely fields that will see significant levels of disease by the end of grain fill, it is already clear that other fields will escape yield-limiting damage.

Several factors are working together to limit the activity of gray leaf spot in corn fields. For one, widespread droughts in 2007 and 2008 resulted in low levels of disease those seasons. Low disease levels on leaves of previous crops means less spore inoculum in the field the following season.

In addition to low levels of inoculum to start this growing season, weather hasn’t been particularly favorable for the disease for the past month or so. Gray leaf spot is favored by warm, muggy weather for days on end, and temperatures have been cooler than normal with many days of relatively low to moderate dew points.

I am expecting that this will be a season where fungicides will have relatively little effect on yield and standability in many corn crops. Yes, some will show a benefit, but others—perhaps many others—won’t. I hope producers who apply fungicides to corn are leaving one or two untreated strips in each field, so as to see for themselves with the yield monitor whether a particular spray was worthwhile. Untreated strips help you decide how important fungicides will be in your future crop-production plans.

SOURCE: Paul Vincelli