As we all know by this point, an unprecedented number of corn was planted much later than usual this season. While late-planted corn is generally associated with lower than average yields, late planting alone is not always a limiting factor. If Mother Nature cooperates and we get a good seed set with timely rains, June-planted corn can still result in exceptional yields.
With late-planted corn, it will be important to keep a close watch on the crop as many pests and diseases can affect the crop at an earlier growth stage. A couple of key diseases come to mind when we think about late-planted corn in a wet, humid season. The first is gray leaf spot (GLS), which can be identified by gray-tan rectangular lesions on the leaves (Figure 1). GLS infects the lower canopy first and works its way up the plant. Typically, it is not observed until after silking; however, this season it may be present at an earlier growth stage. GLS overwinters in corn residue and can survive for more than one winter. No-till fields and heavy corn rotations have the greatest risk.
The second disease to keep an eye out for will be southern rust. I am sure many still remember the yield losses caused by southern rust in 2016 and know that it is not a disease to take lightly. It can be identified by the small, circular, orange-colored pustules present on upper leaf surfaces. Many times, southern rust will look like someone dusted the plant with cinnamon. Southern rust is typically quite aggressive and can be very dense on infected tissue. As with GLS, southern rust is favored by warm, wet weather. The key difference is southern rust does not overwinter in the Midwest and must be blown up to the Midwest from warmer southern regions. Typically, southern rust would not arrive until later in the season when yield has already been determined, but with the late planting and abundance of storms from the south this year, it is possible we may see southern rust early enough to cause economic loses.
Scouting our corn fields this year is going to be very important to help ensure that pests and diseases are held in check. In many cases, using a fungicide as a preventative before the disease spreads is key to protecting yield potential. It is important to continue scouting after a VT-R1 fungicide application to help ensure control and that we don’t get a late flush of southern rust that could still damage yield.
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