Patrick E. Lipps, Anne E. Dorrance, and Dennis R. Mills
The Ohio State University
Gibberella stalk rot-note small, black perithecia near node
Gibberella stalk rot-noterotting of stalk pith and pink coloration
Stalk rots appear in all corn producing counties of Ohio and are the most important diseases of corn in the state. Direct losses to stalk rots have been estimated at 5-15% annually, but actual losses vary from year to year and from one location to another. In seasons particularly favorable for disease development, plants may die prematurely. Such early killed stalks have lightweight ears and poorly filled kernels. More frequently, however, the greatest damage is caused by stalk breakage or lodging. Lodging makes harvesting difficult and many ears are left in the field. Corn producers should be aware of the major stalk rots in the state because of their prevalence and potential for causing severe losses.
Gibberella stalk rot, caused by Gibberella zeae, and anthracnose stalk rot caused by Colletotrichum graminicola, are the most common and destructive stalk rot diseases in Ohio. Diplodia stalk rot (Diplodia maydis) can also be found. Specific information on anthracnose stalk rot can be obtained from fact sheet AC-22 entitled "Anthracnose Leaf Blight and Stalk Rot of Corn."
Gibberella zeae survives from year to year on infested corn stalks and roots left in the field. The fungus typically invades the base of the corn stalk. Tissue is usually resistant up to silking, after which the fungus spreads from the roots to the stalks. Occasionally, invasion may occur at nodes above ground, behind the leaf sheath, or through wounds made by corn borers, hail, or mechanical injury. If plants are infected before full maturity, symptoms first appear as a sudden onset of grayish-green color of the leaves, the lower part of the stalk turns from dark green to light tan, and the pith inside the stalk becomes soft. When diseased stalks are split, the pith usually has a reddish or pinkish discoloration and shows signs of deterioration.
Research has proven that plants subjected to stress are more susceptible to stalk rot. Stress results in early maturation and a reduction in carbohydrates in the stalk tissue. Stalk tissues low in carbohydrate levels are more susceptible to invasion by stalk rotting fungi. Corn plants damaged by fungal leaf blights or root and stalk feeding insects are more susceptible to stalk rot. Extreme weather conditions, unbalanced soil fertility, and high plant populations are predisposing factors that contribute to high stress conditions.
Corn growers should remember that every cornfield is unique. The factors favoring stalk rot in one field may not be important in other fields. Hybrids that stand up well in one area of the state may be severely lodged at other locations. This could be due to soil type, cultural practices, crop rotations, or other factors. Although no one control measure will eliminate stalk rot problems, the following recommendations should be considered and adopted according to the grain needs and management system used by the grain producer.
Additional information is available from your local Extension office or The Ohio State University web site Ohioline at: http://ohioline.osu.edu
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
TDD No. 800-589-8292 (Ohio only) or 614-292-6181