Does Corn Stunt Pose a Risk to the Midwest?

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.