The “corn leafhopper” is a tiny insect that is responsible for transmitting a hugely devastating pathogen – corn stunt disease. Native to Mexico, the insect has spread extensively across the Americas, including to the U.S. starting in the 1940s. Typically limited to warmer-climate states in the South, sporadic outbreaks have caused extensive economic losses ever since. Last year, corn leafhoppers were detected as far north as Wisconsin and experts say the pests could repeat their far northward spread again this year.
Corn leafhoppers reproduce only in corn and its relatives. Adults are tan in color and only about an 1/8 of an inch long. Its most distinguishing feature is two dark spots located between the eyes, which are visible using a 10X hand lens. The nymphs have no wings and are green to tan in color. They run rapidly across the under surface of the leaf when disturbed and may move from side to side and even backwards. Both adults and nymphs like to feed inside the whorl, particularly in young corn. Later, as the plants grow, they move out onto the underside of the leaves.
Corn leafhopper causes damage in two ways. First, leafhoppers directly feed on the plant, sucking out juices. Heavy populations can cause the leaves to dry; also, both the adults and nymphs produce sticky honeydew while they feed, which gets on the corn leaves. Black sooty mold frequently grows on the honeydew, reducing the photosynthetic capacity of the plant.
Secondly, corn leafhoppers transmit a pathogen called Spiroplasma kunkelii, a bacteria-like organism that causes the disease corn stunt. Corn stunt is much more debilitating to the plants than the direct feeding damage caused by the leafhopper. The pathogen responsible for corn stunt overwinters within the adult leafhopper, so leafhoppers emerging from overwintering in early spring can be infective, as can later generations. Corn stunt causes plants to be stunted and can cause significant yield losses.
Corn stunt symptoms show as chlorosis and/or reddening of leaf tips. 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. After that, the shorter corn plant produces auxiliary buds and multiple ears with loose or missing kernels.
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. Once corn stunt disease can be seen, plants are already infected and there is nothing farmers can do. Management strategies must focus on the insect.
While corn leafhoppers and corn stunt have seen sporadic outbreaks in the U.S. in the past, it’s mostly been concentrated in warmer states, primarily California, New Mexico, Texas, Arkansas, Louisiana, Mississippi, and Florida. However, during the 2024 growing season, the corn leafhopper spread widely throughout U.S. corn growing regions, with many Midwestern states seeing the insects for the first time.
The leafhoppers wide expansion last year is thought to have been aided by Hurricane Beryl, which hit Texas in early July. Missouri and Oklahoma were reporting corn leafhoppers by August, and by late in the season, the insects had spread to several major corn-producing states, including Illinois, Iowa, Minnesota and Nebraska, according to University of Missouri.
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. Because the disease is new in so many states, there are gaps in tested management strategies. Still, if you suspect corn leafhoppers or corn stunt disease, it is best to consult your local university extension for the lates recommendations, as they are all appear to be working on raising awareness and finding solutions.
Kansas State Extension row crop specialist Rodrigo Onofre says that based on reports from last year, the double-crop or later-planted corn was at higher risk for corn leafhoppers and corn stunt. It’s thought that corn leafhoppers may first go to younger plants and then move to double-cropped corn as it emerges. The key is to plant as early as possible, Onofre says, to get the corn up and growing past the V8 stage, when infection of corn stunt is less common. (Sources: University of Missouri Extension, University of Kansas Extension, Successful Farming)
