A corn disease and its insect vector were recently documented in New York State for the first time. Researchers at Cornell University found corn stunt and the corn leafhopper in four noncontiguous New York counties in October 2024. Growers should be aware that both could appear in Vermont in future years and that corn stunt can significantly reduce yield.
“The causal agent of corn stunt, Spiroplasma kunkelii, belongs to a specialized class of bacteria known as mollicutes,” wrote Gary C. Bergstrom in his November 4, 2024, blog, Corn Stunt: A New Disease and a New Insect Vector for New York State. Professor emeritus of Cornell’s Plant Pathology and Plant-Microbe Biology Section of the School of Integrative Plant Science, Bergstrom wrote that these mollicutes live in the corn leafhopper, Dalbulus maidis, and in the phloem sieve elements of specific plant hosts.
Below, we’ve summarized Bergstrom’s information on the symptoms, history, and management of corn stunt. For more detail, please see his blog.
After feeding on infected plants, the corn leafhopper transmits the pathogen as it feeds on healthy plants, but corn stunt symptoms don’t generally appear until about a month later. The most severe symptoms occur when corn is infected at early growth stages (from VE to V8), and they’re similar to symptoms from other stressors, including drought, soil compaction, and phosphorous deficiency. These symptoms include white, yellow, red, or purple stripes on leaf blades and sheathes, as well as premature senescence. Symptoms more unique to corn stunt include significant ear stunting and abnormalities, such as poorly filled ears, no ears or multiple ears at the same node.
Corn stunt could occur again in New York in future growing seasons and would cause significant yield losses. In the past decade, the pathogen has been active in some southern and eastern states, but it has only reached epidemic proportions in Texas, Florida, and California, as well as in Mexico and Central and South America. The weather systems that moved from south to north in 2024 likely transported the corn leafhopper farther north than usual. If the same systems don’t recur in future years, corn stunt may not reappear in the northeast U.S. Many people expect that the corn leafhopper can’t overwinter in northern climates, but climate change may alter that. Plant pathologists and entomologists in affected states are collaborating to monitor the pathogen and leafhopper vector in 2025.
Managing corn stunt begins with awareness, accurate diagnosis, and regional monitoring. Though plant breeding has developed corn varieties resistant to the pathogen, they aren’t suitable for northern climates. “Management of corn leafhopper populations with insecticides at corn vegetative stages to reduce corn stunt deserves further investigation,” Bergstrom wrote. “My principal advice to New York growers in 2025 is to plant corn at the earliest recommended date to avoid arrival of leafhoppers at the most vulnerable plant stages for infection by spiroplasma.”
Figure 1 (left). Corn leafhopper, Dalbulus maidis, the insect vector of corn stunt spiroplasma, is characterized by two prominent dark dots between its eyes and a deeply imbedded V-pattern on its upper thorax. Photo courtesy of Dr. Ashleigh Faris, Oklahoma State University.
Figure 2 (right). Corn plants testing positive for corn stunt spiroplasma showed stunting, leaf reddening, and abnormal ears in (A) Erie County and (B) Jefferson County, New York, near the end of the 2024 growing season.