Scout Fields for Corn Leafhoppers

JEFFERSON CITY, Mo. (DTN) -- Farmers with late-planted or double-crop corn should be on the lookout for the corn leafhopper, a tiny flying insect capable of transmitting the potentially devastating corn stunt disease. Within the past week, the pest has been detected in south-central Kansas and southwest and central Missouri, mirroring a pattern similar to last season.

Rodrigo Onofre, row crop plant pathologist at Kansas State University, reported the presence of corn leafhoppers on July 9 in Reno County, Kansas. On July 10, Ivair Valmorbida, University of Missouri Extension entomologist, reported the insect was found in Lawrence and Boone counties in his state.

"The detection of corn leafhoppers in Lawrence County this year lines up with the corn stunt symptoms we saw in southwest Missouri last year," Valmorbida said during a field day event last week. "It takes 30 to 40 days for symptoms to appear in corn, so finding corn stunt in August last year meant the leafhoppers were already here in July."

CORN STUNT YIELD LOSSES

Historically, corn leafhoppers are a pest in Central and South America. The insect was first reported in the United States in the 1940s and was considered an occasional pest in parts of Texas, Florida and California. In 2024, the pest was detected much farther north, including major corn-producing states such as Illinois, Iowa, Minnesota and Nebraska.

No larger than a grain of rice, corn leafhoppers affect corn health and yield both directly and indirectly, Valmorbida said. They cause direct damage to corn plants by feeding on leaves with their piercing-sucking mouthparts. As they feed, the insects excrete honeydew, which can lead to black sooty mold, impeding photosynthesis and negatively affecting plant health.

However, it's the indirect damage that's of greatest concern. Corn leafhoppers can transmit both bacterial and viral pathogens associated with corn stunt disease. With severe infection, 100% yield loss has been reported in South America.

Corn stunt spiroplasma, a bacterium, is considered the predominant pathogen associated with corn stunt disease. Symptoms appear as chlorosis and/or reddening of leaf tips. After that, the shorter corn plant produces auxiliary buds and multiple ears with loose or missing kernels.

SCOUT FOR LEAFHOPPERS

The range and severity of corn stunt symptoms can vary and are influenced by the corn's growth stage when infection occurs, the amount of inoculum present, the corn hybrid and environmental and weather factors, Valmorbida said.

K-State's Onofre stated that the exact corn growth stage at which scouting should cease is unknown. In the past, scouting has been encouraged through the V8 growth stage, but more studies are needed to verify the validity of that recommendation, he wrote.

Valmorbida said that the corn in Lawrence County where the leafhoppers were detected was at the V8-V9 growth stage. He previously told DTN that if leafhoppers feed on the crop around V5 and they're carrying the pathogens, there's a greater chance of the corn stunt disease to cause significant yield losses.

"If they show up later in the season after tasseling, that's not likely to cause any problem to corn in the field," he said.

Valmorbida recommended using yellow sticky cards, sweep nets and visual inspections for scouting cornfields. He said that corn leafhoppers can sometimes be confused with other pests, including the aster leafhopper.

Scouting cornfields at least once a week is crucial to detecting corn leafhoppers. If no action is taken until honeydew or black sooty mold is visible, it's probably too late, the entomologist added.

Both Onofre and Valmorbida noted that there is currently no economic threshold for the corn leafhopper. However, managing the insect is the best means of preventing yield losses to corn stunt disease.

Early planting can reduce the chances of infestation, and insecticidal seed treatments can offer control of the pest up to about the V3 growth stage. After that, growers should consider foliar insecticides if corn leafhoppers are present before the crop reaches reproductive growth stages. Onofre said broad-spectrum insecticides are suggested as the best option for controlling corn leafhoppers. However, the occurrence of multiple waves of the pest throughout the crop's early growth stages means that insecticides might not be a bulletproof option to prevent corn stunt.

This spring, the University of Missouri Extension released a publication to help farmers identify corn leafhoppers. It also provides scouting and management recommendations. Download it here: https://extension.missouri.edu/….

Jason Jenkins can be reached at jason.jenkins@dtn.com

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