Now is not the time to stop scouting. It may not be pleasant out there (think pollen and hot), but the weather the past couple of weeks has been favorable for gray leaf spot development. Gray leaf spot development is favored by mean daily temperatures between 72 F and 85 F, and high humidity (higher than 90%). I have had several reports this past week of fields in which the gray leaf spot has developed up to the ear leaf. Northern leaf blight development has also been progressing in several fields in central Iowa.

I have been scouting my field plots the past couple of days and also have noticed that gray leaf spot and northern leaf blight have developed rapidly in the past two weeks. One thing I noted was disease severity was hybrid specific. I have several hybrids in my plots, but only one or two may be at threshold for a fungicide application (disease present on the third leaf below the ear leaf or higher). The affected hybrids always are rated more susceptible to disease.