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Diplodia Ear and Stalk Rot

August 11, 2000

The time is here for early ear-rot and stalk-rot development. Eric Suits of Trisler Seed reports diplodia ear rot reaching about 6% to 7% in some fields near Allerton and Sidell, Illinois. Eric indicted that many husks and ears were already fully infected. Environmental conditions this season have set the stage for good development of ear and stalk rots. Leaf blights, insect damage such as corn rootworm feeding, unbalanced fertility, extreme weather conditions, and hail damage are the primary factors that individually or in combination predispose corn plants to infection by stalk rots. Specifically, this year, look in fields that were affected earlier in the season by common rust infection and in fields showing nitrogen deficiency.

Fungi cause the ear and stalk rots that render the most damage in Illinois. 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 in particular of one ear and stalk rot called "diplodia."

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. Diplodia stalk rot is easily identified: infection begins at the nodes, and as the disease develops, small, black specks that cannot be scraped off form near the nodes.

Scouting for stalk rots is a fairly easy endeavor. Evaluate 20 plants at each of 5 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% 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 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%. However, incidences above 10% to 15% 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 rot.--Suzanne Bissonnette

Author: Suzanne Bissonnette

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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