As we enter into the post-pollination phase of the season, many corn diseases will accelerate their development. So far, leaf diseases have not been very severe, largely because of the dry weather. Common rust is evident in many fields but only at very low levels, and traces of gray leaf spot and eyespot can be found. Gray leaf spot has the potential to increase rapidly during the post-pollination period, even when rainfall is not plentiful. Scouting for gray leaf spot and other leaf diseases should continue in seed production fields. In commercial grain production fields, it also is a good idea to scout for leaf diseases. Although current prices are not favorable for using a fungicide in grain production, it is important to know whether leaf diseases are going to affect yields. Scouting could alert you to potential yield losses that may otherwise go unnoticed until harvest time. The severity of leaf diseases 2-3 weeks after pollination is a good indicator of whether there will be a yield impact, and this knowledge can help in making plans for crop rotation and hybrid selection for the next 2 years.
|Gray leaf spot symptoms.|
|Early symptoms of anthracnose stalk rot in corn.|
Stalk rots also appear after pollination and this year we are in a position for serious problems with anthracnose and other stalk rots. I have already had a couple reports of top dieback in corn. Extension field specialists are reporting a great deal of root lodging due to poor root development, root rot, and rootworm injury, which are all precursors to stalk rot problems. The wet spring resulted in poor root establishment and the initiation of root rot infections; both of these conditions will lead to stalk rot development, especially if plants continue to be under moisture stress. It will be important to identify fields with impending stalk rot problems so that harvesting can be planned accordingly.
This article originally appeared on pages 156-157 of the IC-486(20) -- July 30, 2001 issue.