This certainly would not appear to be a year where leaf disease will be a major factor in threatening corn yield, at least not in areas where it was dry early. And now that it's drying out, perhaps too much, in the western Corn Belt, disease activity, if any, may slow there as well.
Until last week, there were simply no signs of disease on any plants at the Farm Progress Corn Illustrated plots located in south-central Indiana, near Edinburgh. The plots continue to get just enough rain to hang on, although it's obvious yield in non-irrigated sections of the plot are already likely hurt. Jim Facemire, who farms the land where the plots are located, says he's received 0.9 inches of rain in July- in seven individual rain events! He's only received roughly 3 inches since May 1, and over 1 inch of that came in one rain during the third week of June.
Dave Nanda, consultant for the plots and long-time plant breeder, discovered a minimal amount of what appeared to be southern corn leaf blight on one hybrid. It was one of 60 hybrids planted so that he could study individual hybrid performance side-by-side. There is one row of each hybrid- 10 per range, with each one representing one/one-thousandth acre.
He also noted gray leaf spot on corn in the historic plot on USA 13, a hybrid from more than five decades ago. It's likely gray leaf spot wasn't even a factor when that hybrid was developed and released, Nanda says. It would appear susceptible to it, although at this point, it's still covering only a relatively minor portion of the leaf area on some leaves of some plants.
Disease becomes a concern when it moves above the ear leaf, and when humidity levels and temperatures favor leaf development. Humidity levels remain low on most days in the eastern Corn Belt- unusually low for July.
There was also a minimal amount of disease noted in the high-yield plots that are irrigated. But again, those plots are already pollinated, and the amount of disease is minimal.
The biggest threat if leaf disease comes in from now on is how it might affect drydown and possibly premature death of the plant. Agronomists dealing with areas that have faced moisture-stress all season long, on the dry side, are concerned that if it stays dry, plants may take nutrients from the stalk to finish filling ears as best they can. That could set fields up for stalk rot due to stress. It will be a fall where each field should be watched carefully for lodging potential, particularly in stressed fields.