The past two weeks were a critical period in determining the extent of yield loss to gray leaf spot. For most producers, the news is good. Although the disease appeared early this year, it has not yet begun to develop rapidly, and I have not seen or heard reports of fields with significant damage to the ear leaf. If the disease does not damage the ear leaf or the leaves above the ear within a few weeks of silking, yield loss will be minimal.

Now that many fields are moving well into the grain-fill period, they are less vulnerable to yield losses caused by leaf diseases.

Some fields are not yet safe from damage. Late-planted fields that have recently silked still could suffer substantial yield losses if the disease picks up steam over the next few weeks. Typically, gray leaf spot development accelerates late in the season, and this could spell trouble for fields planted in June in southeast Iowa, especially if they are corn-on-corn.

We will probably see severe gray leaf spot in some fields before the season is over, but the later this happens, the better. I am certain that there will be some losses, but all indications are that the damage will be much less widespread and less severe than the last two years.