We have reported both here and in print that in most of Indiana, this was not even a good year for corn leaf diseases. Judging at county fairs this summer, it was hard to even find a small lesion on leaves to explain to the 4-H'er what lesions look like. Of course, anyone who saw lots of lesions probably wouldn't bring that specimen to the fair.
However, Dave Nanda, a crops consultant and director of genetics and technology for Seed Consultants, Inc., says he noticed the same thing in the field. Over most of the state, where areas were dry and temperatures were very hot, he saw little if nay foliar disease during most of the season.
That's still true for areas that have received very little rain. Those areas that received very little rain in July and most of August included a large area within several counties in central, west central and east-central Indiana.
However, when Nanda visited farms where rainfall was more normal, and his visit was within the last two weeks, he has noticed several lesions of gray leaf spot. In some areas where rainfall has been plentiful, gray leaf spot is rampant on nay hybrid that is very susceptible to it, and that wasn't protected by a fungicide, he notes.
"This is probably going to be the year of gray leaf spot, but only if you had enough rain for the disease to develop," Nanda says. "If you are in an area that still hasn't received rain or only got some within the past few days, then you're still likely not going to see much disease."
Foliar diseases in corn can cut into yields and prove detrimental because they destroy the factory that turns sunlight into sugars for the plant through the process of photosynthesis. If the factory is smaller because part of it has been wiped out by disease lesions, then it will be more difficult to produce as much yield as might have been possible otherwise, Nanda notes.The situation is most severe when the lesions become numerous above the ear leaf. That's because about 80% of the energy is captured by the top few leaves on the plant at that point in the season, Nanda says. So those top few leaves are critical in terms of final yield potential.