Corn stunt vectored by leafhopper
If you’ve noticed what first appears like deer damage in your corn that causes the plant to turn reddish-purple, you might have corn stunt.
Mike Stanyard, representing CCE’s Northwest New York Dairy, Livestock & Field Crops Program, presented on corn stunt at the recent Corn Congress hosted by Cornell Cooperative Extension.
“We know corn stunt is vectored by corn leafhopper,” Stanyard said. “And it’s caused by the pathogen Spiroplasma kunkelii.”
A new pest in New York, the corn leafhopper measures about one-eighth of an inch long with a torpedo-shaped body, yellow to tan coloring, two dark spots with haloes on its head, no facial markings on the ventral side and a deep “V” shape on its thorax.
Stanyard noted that the corn leafhopper can only reproduce on corn. Its lifecycle from egg to adult is about three to four weeks and it needs a living host year-round.
“It doesn’t overwinter in New York,” he said. Occasionally, the corn leafhopper is seen in south Texas, California and Florida. Tropical storm systems have brought the pest to New York.
Signs of corn leafhopper infestation include honeydew residue caused by the pests’ suckling, which in high populations leads to sooty mold.
The nymphs hatch disease-free; however, corn leafhopper acquires the pathogen in about an hour of feeding on an infected plant. After two to four weeks, the pathogen replicates before corn leafhopper can transmit the disease.
The symptoms on the corn appear within three to four weeks of inoculation. Stage VE to V8 corn is the most susceptible to disease and yield loss.
“If we get it later, you don’t see a lot of yield loss,” Stanyard noted.
In plants affected by corn stunt, farmers would notice bushy plants and short internodes, along with reddening leaves and most of the stem. The stalk would also over-produce ears and have missing and light kernels.
CCE agents can help farmers diagnose corn stunt. “It’s easy to misdiagnose it as it looks like everything else: nutrition deficiency, drought and heat stress,” Stanyard said.
That’s in part what has helped corn stunt spread: farmers had it in their fields without knowing it. Corn stunt was first found in 2024 in Erie County, where a farmer from South America said he recognized the disease. Testing revealed his hunch was right.
Since then, corn stunt has been confirmed in Jefferson, Monroe and Yates counties.
“Given more time for scouting pre-frost, many more fields likely would have been diagnosed,” Stanyard said.
His team plans to continue placing sticky traps throughout the state’s corn fields to obtain samples of the pests, along with samples of corn stunt to study. Stanyard encouraged farmers to submit leafhopper species and affected corn samples via next day delivery for Extension agents to study further. The samples require a molecular test for positive identification of S. kunkelii.
