Much corn still remains to be harvested in our area. While ear rots have been a significant concern this late season, the longer the corn is out in the field the more fungal stalk rots become an issue. Stalk rots are actually quite prevalent each year in the corn crop. We don't always see or note them because many have ceased scouting efforts by the time diagnostic symptoms of stalk rot show up in a field. In fact stalk rots are the most common diseases of field corn in Illinois. Yield losses result from premature stalk or plant death, so ears are poorly filled or light weight, and harvest losses result from stalk breakage or lodging. Problems with ear rots are usually greater where lodging occurs, particularly when the harvest season is wet.

Development of stalk rots is favored by an early season environment that encourages kernel set and a late season environment that is stressful. Stresses may include an excess or lack of moisture, nutrient deficiency or imbalance, excessive cloudiness, insect, nematode, hail, or other mechanical injury to the stalks or roots, foliar leaf blights, and an excessive plant population. Extended periods of very dry or wet weather prior to pollination followed by an abrupt change for several weeks after silking, favor the development of most stalk rot fungi. Also, injury to roots, stalks, or leaves by other diseases, insects, nematodes, hail, or equipment also can increase the incidence of stalk rot. Injuries created by European corn borers, corn rootworms, and other insects often provide avenues of entry for stalk rot pathogens.

Our most common stalk rot diseases caused by fungi in Illinois include Gibberella, Anthracnose, Fusarium, and Diplodia stalk rots. Stalks infected with the Gibberella fungus have a characteristic pink to reddish discoloration of the pith and vascular strands. Fusarium stalk rot is very similar to Gibberella, except that the discoloration of infected tissues commonly varies from whitish pink to salmon. Anthracnose which is very common every year is unlike most other stalk rots because it can often destroy several internodes of the stalk. Anthracnose can also be seen as a top-kill or early season leaf blight. A shiny black or dark brown discoloration of the rind late in the season is typical of anthracnose. This black discoloration usually extends up the stalks for several internodes as if the stalk was sprayed with black spray paint. Diplodia stalk rot, also quite common this year, is seen a little black specks located at the lower plant nodes on the stalk rind.

Unfortunately stalk rots cannot be entirely controlled. Damage can be reduced by use of an integrated control program. Plant well-adapted, disease-resistant hybrids; practice balanced soil fertility; control insects; plant the recommended plant population; avoid stress through proper irrigation, soil management, and foliar disease and weed control; practice regular field scouting; and harvest when the crop is mature to prevent losses from lodging. In other words, take special care to avoid the stresses you have control over and stalk rots won't be as troublesome.