By STACEY CAMPBELL
Cottonwood Extension District
Last year’s growing season brought to Kansas a new disease to corn, corn stunt spiroplasma and its associated vector the corn leafhopper insect.
It was confirmed in 26 counties in 2024. Active field scouting last year confirmed active leaf hoppers in many additional counties. Although the majority of the positive reports are from field corn, also confirmed corn stunt spiroplasma in sweet corn as well.
High levels of disease were found in late-planted and double-cropped corn, leading to potential yield reduction. So be aware that late-planted and double-cropped corn is more at risk of contracting corn stunt disease. Early planting of corn is advised as leafhopper infestations, and corn stunt disease will increase as the season progresses. Removal of volunteer corn plants following the growing season is also advised to reduce overwintering sites for adult corn leafhoppers.
Symptoms of the disease may include shortened internodes, which can result in a stunted stature of the corn plant as well as leaves with red discoloration. Because other factors in the environment can cause red or purple discoloration in corn, laboratory testing is important to diagnose corn stunt disease and distinguish it from other stressors. Corn stunt disease can result in yield loss due to severe plant stunting, smaller ear size and loose/lost kernels.
In the past, corn stunt disease has been limited in distribution to southern Texas, Florida, and California in the United States.
Corn stunt is caused by a wall-less bacterial pathogen called corn stunt spiroplasma. The corn leafhopper can also transmit additional pathogens, either singly or in combination with the corn stunt spiroplasma.
To date, only corn stunt spiroplasma has been detected in Kansas. Additional research is needed to determine the presence of other pathogens vectored by corn leafhopper in Kansas.
This disease is spread only by the corn leafhopper. Corn leafhopper acquires pathogens within minutes of feeding on infected corn plants but it can take up to 30 days for the leafhopper to be able to infect healthy corn plants during feeding events.
Although the infestation by the corn leafhoppers usually begins at the early crop stages, and the transmission of the pathogens occurs in the vegetative growth stages, symptoms of corn stunt disease only appear later in the season, generally 30 days after leafhopper feeding, when corn has already reached the reproductive stages.
Chemical Control
Corn stunt disease incidence will not be reduced by insecticide control. If you see disease symptoms in the field, the plants have already been infected. Infected plants will not show symptoms for one month. If the corn is mature enough, then infection may not impact corn kernels.
According to Corteva Agriscience, insecticidal seed treatments consisting of imidacloprid and clothianidin can provide control of corn leafhoppers up to the V3 growth stage. After that, plants are susceptible to acquiring the corn stunt pathogens through leafhopper feeding.
The corn leafhopper is relatively simple to identify under magnification. These leafhoppers are light tan to yellowish-white in color and approximately 1/8” long. Two distinct dark spots between the antennae and eyes are very characteristic of this species. Nymphs lack wings and can vary in color. Like most leafhoppers, all stages move quickly when disturbed and hide in shaded areas of corn plants.
All stages can be sampled using a sweep net; a video showing how to sample for corn leafhoppers in mature corn canopies can be found here: https://youtu.be/QgLuWWSwHWU.
If you ever have any questions or during the growing season need me to look at any of your corn fields, please give me a call at 785-628-9430.
Stacy Campbell is a Crop Production Extension agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at [email protected] or by calling 785-628-9430.