Last July, Extension specialists in southwest Missouri started to notice strange symptoms in their corn crop: purpling in the leaf tips, stunted plants, and abnormal ears.
Then, they started to notice the corn leafhoppers.
“We estimate from the time we first found them in July to the end of the season, 90% of the state was covered by corn leafhoppers,” said Mandy Bish, an Extension crop pathologist at the University of Missouri.
A DNA analysis of diseased plants confirmed suspicions: Missouri had its first documented case of corn stunt.
What Is Corn Stunt?
First identified in Argentina in the 1990s, corn stunt disease is common in Latin American countries. Its primary cause is the bacterium Spiroplasma kunkelii, spread by corn leafhoppers.
When left unmanaged, corn stunt can cause significant yield loss. In Argentina, for example, yield estimates dropped 20% between December 2023 and April 2024 due to corn stunt worries.
While historically, corn stunt has been seen sporadically in the U.S., the spread of corn leafhoppers and the disease in 2024 was prevalent enough to cause concern.
“At this point, I would say farmers should have a healthy respect for corn stunt,” Bish said. “It’s not like tar spot, where, now that it’s here it’s always going to be here. Until we know how far north the leafhoppers can survive the winter, it’s hard to understand how much of an annual risk this is.”
Corn Leafhopper Characteristics
Adult corn leafhoppers are typically light in color, and have torpedo-shaped bodies around 1/8 inch long.
“The main characteristic of identification, although you might need a hand lens to see them, are two very prominent black dots between the eyes,” said Brad Hopkins, a product agronomist for Pioneer.
The leafhoppers are often found in high populations and can be seen moving from plant to plant. Yellow sticky traps are an effective option for identifying the pest, and further testing can identify whether field populations carry disease.
In optimal conditions, the progression from egg to adult stage is 24 days. Adult corn leafhoppers can live up to three months, and multiple generations can exist in one growing season.
“Females can typically lay about 15 eggs per day,” Hopkins said. “If they have a life cycle of two to three months, you can see how quickly they can develop a large population.”
The leafhoppers have piercing, sucking mouths, used to feed on the corn’s phloem sap. The pests spread corn stunt by infect-ing healthy plants during this feeding process.
“It only takes about an hour of feeding for the insect to acquire the Spiroplasma,” Hopkins said. “There is a fairly long latency period within the leafhopper itself. I’ve seen literature reporting 17–23 days for Spiroplasma to develop inside the leafhopper, where it’s able to be spread to healthy plants.”
Corn leafhoppers are able to move several miles locally, and wind patterns over large areas can exacerbate their spread. Some experts believe high populations of corn leafhoppers in Latin America paired with weather events, such as Hurricane Beryl, contributed to 2024’s increased pest pressure.
Wheat and gamagrass can also serve as host crops for corn leafhoppers, although the pests can only reproduce in corn plants. Tracking populations in the coming season can give experts a better understanding of future threat levels.
Tomasz Klejdysz, Getty Images
Corn Stunt Symptoms
After infection, it takes 30-50 days for the pathogen to establish itself in the corn plant and for symptoms to be seen. While there are no rescue treatments currently available, accurate identification can aid research and future risk management.
“Symptoms and their severity are really dependent upon when infections occur,” said Jason Woodward, a product agronomist for Pioneer. “Plants that are infected shortly after emergence are going to exhibit much more severe symptoms.”
Leaf discoloration may start on the leaf margins and develop into pronounced striping or mottling. Shortened inner nodes and reduced plant height may be noted, but plants infected later in the growing cycle may show little stunting.
Infected plants often have poor ear development, presenting as malformed ears, reduced or discolored kernels, and reduced grain quality.
DNA analysis for the disease pathogen can confirm the disease presence.
What Now?
While much about corn stunt in the U.S. remains unknown, some management decisions can reduce risk of yield loss. Due to the lack of rescue treatments, controlling corn leafhoppers is essential to stop the spread of corn stunt.
Fields that see repeated corn leafhopper pressure may benefit from insecticide treatments. Seed treatments can provide protection through V3, and foliar application products can be used later in the season.
“The most critical time for corn to be protected is from emergence to V8,” Bish said. “That’s going to involve early detection and management of the leafhopper, as populations can grow quickly.”
Farmers who suspect corn stunt should contact local Extension services for verification and guidance. Following a corn stunt outbreak, a diligent volunteer corn management program should be implemented to disrupt corn leafhopper life cycles.
“Make sure to stay informed,” Hopkins said. “If this becomes an issue going forward, it’s really going to be industrywide. Make sure you’re leveraging your local agronomy teams and university Extension. They are the folks who are going to be the best connected and grounded into what’s working.”