ONTARIO GRAIN FARMER CROP SIDE 29 An unexpected pest made its way from the southern U.S., moving as far north as the Great Lakes region in 2024. Corn leafhopper, Dalbulus maidis, is native to Mexico and has been infesting corn from Argentina to the southern U.S. for decades. Corn leafhoppers (CLH) were carried into our region, potentially from tropical storms or hurricanes, and were detected in Minnesota and New York in late summer. Though it was unexpected, this could become more common with stronger storms to carry them in and milder winters that allow them to overwinter closer to Ontario. Late summer arrivals have a minor impact, but any earlier, when the vegetative stages of corn are still available, could have a major impact here. Corn leafhoppers are light yellow to tan in colour and wedge-shaped, with the adults being slightly larger than potato leafhoppers (three to four millimetres in length). Two black dots between the eyes, bordered with a light white halo, distinguish them from other leafhoppers, though no other leafhoppers colonize on corn (Figure 1). Adults have transparent wings, while the nymphs lack wings and like to walk sideways very quickly when disturbed. Corn leafhoppers evolved on corn and its close relatives (teosintes) but has been known to feed on other grasses like millet, sorghum, and even wheat, though it cannot complete a lifecycle on these other grass types. Corn leafhopper cause direct injury to corn by piercing leaf tissue, but more concerning is that they vector several corn-stunting pathogens, including corn stunt spiroplasma (CSS), maize bushy stunt phytoplasma (MBSP), and maize rayado fino virus (MRFV). Symptoms of these pathogens include yellow stripes and reddening of the leaf margins and mid-ribs, tillering and smaller ears, shortened internodes, poor kernel fill, and yield loss (Figure 2). Honeydew can also build up in heavy CLH populations, causing sooty mould to develop, impeding photosynthesis, and impacting overall plant health. Corn stunt symptoms do not show up until at least 30 days after transmission, and once the plants are infected, there are no effective treatment options. Scouting and detecting CLH early are key. Yellow sticky traps (also used for corn rootworm) placed at the fields’ edge can help with detection. A pilot corn leafhopper trap network has been set up this summer across different regions of the province to see what we find. Corn leafhopper, a new pest threat Tracey Baute Crop side with... Tracey Baute, Field Crop Entomologist, Ontario Ministry of Agriculture, Food and Agribusiness Figure 1. Corn leafhopper has two black dots with light white halos between the eyes. Aster leafhoppers also have black dots but have no halos around the dots. Photo credit: Dr. Ashleigh Faris, Oklahoma State University. Also, keep watch for corn leafhopper and corn stunt symptoms while scouting corn. Later-planted corn is more at risk, as corn leafhopper prefer younger corn stages. Look for corn leafhopper on the shady undersides of the leaves or as colonies in the whorl. Their discarded skins from moulting might also stick to leaves for a brief time. Late in the season, keep watch for symptoms of corn stunt disease. If you believe you have found a corn leafhopper or a corn stunt, contact Tracey Baute, tracey.baute@ontario.ca or Albert Tenuta, albert.tenuta@ontario.ca, for verification. In-season corn leafhopper detections are currently being mapped through the Crop Protection Network at cropprotectionnetwork.org/maps/corn-leafhopper. Figure 2. Shortened corn plants with red streaks and poor kernel fill are symptoms of corn stunt disease, vectored by corn leafhopper. Photo credit: Mike Hunter, Cornell IPM.
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