From Dr. John Mueller (Extension Nematologist and Pathologist)
I am not about to comment on what type of weather everyone has endured over the last month other than to say some of you are still in a mild drought and those of us at Edisto REC got 12 inches of rain in May and 5 in April. The weather forecast for the next 10 days indicates most of us will be in a strong afternoon rain pattern. Of course, this is very conducive to fungal foliar diseases on most field crops including corn.
We have been fortunate that despite all of the rain so far incidence and severity of corn foliar diseases have not been equally high. We have not seen common or Southern rust in South Carolina, nor have they found it yet in Georgia. However, since much of the crop is starting to tassel they will probably show up. Northern corn leaf blight is often our most common disease but so far its incidence has been low.
However, one of our newer diseases seems to be quite common and where present seems to be at high levels. Gray leafspot overwinters on crop debris and we have quite a bit of corn this year following a corn crop last year and grown using minimum tillage. For symptoms see attached photo taken last week by Dr. Plumblee in Lexington County. Disease incidence was quite extensive across this field which was just beginning to tassel.
Normally we would consider applying one or two applications of a fungicide on a corn crop depending upon diseases present and the weather forecast. If you have foliar diseases present, especially if you are at or past tasseling, with this weather forecast you should consider spraying a fungicide.
If disease incidence is high in your field or the weather forecast is for lots of rain plan to use a fungicide with 2 or 3 active ingredients. Attached here is this years Crop Protection Network’s annual evaluation of fungicides for the control of foliar fungal diseases of corn.