First case of stunt disease confirmed in Missouri corn fields

Specialists at the University of Missouri Extension have confirmed the first case of corn stunt disease in Missouri, causing great concern for corn producers in the region. The disease, which is transmitted by the corn leafhopper, was discovered in southwest Missouri.

Corn leafhoppers, an insect that can infect corn with three pathogens, lead to the development of corn stunt disease. The first symptoms of the disease include yellowing or reddening of the leaf tips, followed by the growth of multiple small ears with loose or missing kernels, a reduction in plant size, and deformed kernels. Significant yield losses can occur in affected areas.

“Corn stunt is not a common disease and we did not expect it in Missouri in 2024,” said Mandy Bish, a plant pathologist with MU Extension. She also noted that corn stunt significantly reduced yields of the 2024 Argentine corn crop.

MU Extension agronomist Tim Schnakenberg was recently alerted by farmers and agricultural experts to symptoms reminiscent of corn stunt in Christian, Stone, Lawrence and Barton counties in southwest Missouri. The first symptoms observed included red and yellow discoloration of corn leaves and plants, as well as premature drying from the tip of the stalk down.

“At the same time that the leaf symptoms were observed, corn leafhoppers were clearly visible in the field. There is concern that many kernels from the affected plants may not make it into the grain tank of the combine due to the low test weight,” Schnakenberg explained.

He and other agricultural experts sent field samples from the region to Peng Tian, ​​​​head of the MU Extension Plant Diagnostic Clinic. Tian confirmed the disease using laboratory techniques such as polymerase chain reaction (PCR) and gene sequencing.

Infected plants can only grow to about 1.5 meters tall – about half their normal height. Leaves can appear shiny due to the honeydew that the leafhoppers excrete as they feed. This honeydew can lead to black sooty mold, which hinders photosynthesis and negatively affects plant health. Because the pathogens are not fungi, Bish says fungicides are ineffective. Instead, management efforts will focus on controlling the insect population.

According to Ivair Valmorbida, a state entomologist with MU Extension, corn leafhoppers are light brown or yellow and about 3 mm long. An identifying feature of these leafhoppers are two dark spots between the eyes of the adult insects, which are visible with a 10x magnifying glass. Nymphs are green to brown in color and have no wings.

These insects move quickly within and between corn fields, flying or jumping away when disturbed. They are typically found in shady areas of corn, where they rest and feed in the whorls of young plants or hide on the undersides of leaves.

Corn leafhoppers affect corn health and yield by feeding on leaves, sucking plant sap, and transmitting pathogens that cause corn stunting. They only reproduce in corn and related plants. According to Oklahoma State University, corn leafhoppers have been associated with corn since it was domesticated about 9,000 years ago. Tian continues to work with entomologists at Oklahoma State University, who also confirmed the first case of corn leafhoppers in the state this season.

Corn leafhoppers migrate northward by wind-assisted migration from Mexico, where corn is grown year-round. Adult corn leafhoppers are known to overwinter in grasses such as wheat, alfalfa, Johnson grass, sorghum, sugarcane, soybeans, millet, and gamma grass, but reproduce only on corn.

It is generally believed that these leafhoppers cannot survive Missouri winters, but Valmorbida and Schnakenberg plan to continue to watch for corn leafhoppers in southwest Missouri throughout the winter.

Recommended cultural control methods to contain the disease include early planting, crop rotation, and control of wild plants that may serve as overwintering sites for the insect.

Bish warned that other stresses could cause corn to turn yellow and red late in the season. She advises watching for additional signs, such as the presence of leafhoppers and honeydew.

The MU Plant Diagnostic Clinic offers diagnostic services for suspect samples for a nominal fee. Ideally, samples should include stems and leaves. Contact the MU Plant Diagnostic Clinic for more information.

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