Fungal Stalk Rots Probable

August 27, 1999
Environmental conditions this season have potentially set the stage for development of stalk rot in the corn crop. Producers in areas of the state that have had considerable water stress (either too wet or too dry) need to start looking for stalk rots. Leaf blights, insect damage such as corn rootworm feeding, unbalanced fertility, extreme weather conditions, and hail damage are the primary cast of characters that individually or in combination predispose corn plants to infection by stalk rots.

Stalk rots and ear rots that cause the most damage in Illinois are caused by fungi. What these different fungi have in common is that they rob the grain of nutrients during kernel maturation and significantly interfere with stalk integrity. These conditions lead to lodging and lower-quality grain. This season's weather has provided a good environment for the development of a common Illinois stalk and ear rot called "Diplodia." Diplodia stalk rot is easily identified: infection begins at the nodes, and as the disease develops, small, black specks that you cannot scrape off form near the nodes. Diplodia ear rot is first noticed by the bleached appearance of the husk. When you peel back the husk, you will see a white, fluffy fungus. Diplodia will not produce toxins in the grain, but the kernels will be very lightweight and shriveled in appearance.

Other fungal stalk rots that may show up soon are charcoal rot, particularly in droughty areas, and anthracnose stalk rot.

Scouting for stalk rots is a fairly easy endeavor. Evaluate 20 plants at each of five locations in a field. Use the common zigzag scouting pattern to accurately evaluate stalk rot incidence. Begin scouting when the kernels are at 30 to 40 percent moisture. You can use either of two methods to evaluate stalk integrity: The first is to lightly grasp the stalk at waist level and push it about 15 degrees from the vertical. A second method is to pinch the base of the stalk below the first node; stalks that lodge or collapse when pinched should be marked positive for stalk rot. Fields can endure stalk rot incidence up to 10 percent. However, incidences above 10 to 15 percent call for an early harvest to prevent further damage and lodging. Observe the ears for ear rot at the same time you are scouting for stalk rots.--Suzanne Bissonnette

Author: Suzanne Bissonnette