Garden Word of the Day
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European Corn Borers
European corn borers are the larval form of an unassuming tan moth. This invasive pest bores into all parts of corn, millet, and other grain plants, but that’s not all. If corn isn’t available, these pests will also feed on lima beans, peas, peppers, and potatoes.
As far as I know, this pest is currently only found East of the Rockies, but that may change as early as tomorrow. You may as well learn about it today, wherever you are.
European corn borer identification
Known as the European high-flyer, these moths are one inch long with a one-inch wingspan. Females are tan with light brown markings. Males are smaller, with darker markings. If you see an adult at rest you will be able to see the abdomen sticking out from under the wings. European corn borers (Ostrinia nubilalis) can be dark reddish-brown to pinkish gray. They have brown spots on each segment and are just under one-inch long.
European corn borer lifecycle
European high-flyers lay clusters of whitish-yellow eggs on corn and other host plants, usually on the underside of leaves. Females lay two clusters of eggs each night over 10 days. This translates into 400–600 eggs per adult female.
Just before hatching, the eggs become translucent. Then the larvae chew their way to freedom and begin feeding on the host plant. Once they’ve eaten their fill and made a mess of your corn, they enter a pupal state. Inside the chrysalis, larvae transform into adults. In some cases, there may be two pupal stages. I have no idea why.
As daylight hours shorten, larvae enter hibernation. The scientific term is diapause. I wonder if that’s a reflection of “die or pause”—hard to say.
European corn borer damage
As larvae bore into leaves, stalks, and ears, photosynthesis is reduced, nutrient and water transport are slowed, and dozens of points of entry for Fusarium and other pathogens are created. This sets the stage for some very unhealthy, unproductive plants.
Symptoms of European corn borer feeding include clumps of what looks like sawdust (it’s bug poop) on top of mature leaves, frass and damage where leaves emerge from the stalk, and a shot-hole type of leaf damage.
European corn borer management
While immature corn plants can protect themselves against this pest with an antibiotic substance they create, that protection doesn’t last into adulthood. Commercial corn growers often plant varieties of GMO seed corn that contains a synthetic version of a gene from Bacillus thuringiensis kurstaki, an insecticidal bacteria. For the home gardener, there are other ways to manage European corn borers. For one thing, insidious flower bugs, predatory stink bugs, and Trichogramma wasps all prey upon or parasitize these pests, along with ladybugs and lacewing larvae, so you’ll want to avoid using broad-spectrum pesticides.
Beyond that, monitor your corn plants for signs of entry holes. You can also use pheromone traps. You can apply your own Bacillus thuringiensis kurstaki or spinosad to treat severe infestations.
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