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July 14, 2003

Obscure corn pest a 'miner' concern for farmers, entomologist says

WEST LAFAYETTE, Ind. – An agricultural pest rarely seen in Indiana is turning some farmers as white as the discolored corn leaves the insect's feeding produces.

Fortunately for producers, the corn blotch leafminer causes only cosmetic damage to corn plants, said John Obermeyer, Purdue University Cooperative Extension Service entomologist. Seldom does pest feeding result in yield loss.

Unusually large numbers of corn blotch leafminer – Agromyza parvicornis – have been found in fields in southwest and north-central Indiana, Obermeyer said.

"In one 300-acre field near Rochester, Ind., about 85 percent of the plants showed damage," he said.

Farmers unfamiliar with leafminer feeding might confuse leaf damage with herbicide injury, Obermeyer said.

As its name indicates, the leafminer tunnels through corn leaves. The yellowish larva, only one-sixteenth inch to a quarter inch long, gobbles its way from one end of a leaf to the other.

"The insect that causes the damage is a maggot," Obermeyer said. "It's very small and it crawls within the corn leaf. As it does, it feeds away and creates a mine. It looks like a little picture window through the corn leaf as the maggot eats away all the green chlorophyll in the plant.

"As the mines get longer and longer, many of the mines start joining together. It's been noted that the lower leaves on some plants that are severely infested are bleached white."

The leafminer's life cycle is about two weeks, from egg hatch to maggot to pupa to egg-laying fly. Several leafminer generations can infest a field in a crop year.

Farmers with leafminer populations need not worry, Obermeyer said. Insecticide treatments aren't recommended because parasitic wasps usually control the pest.

"These maggots feed only so long," Obermeyer said. "Maggots may destroy the bottom three or four leaves of the plant, but eventually the corn does outgrow their damage. The maggot then completes its life cycle and is not a problem the rest of the season.

"We would encourage producers not to get overly excited about the mining. Insecticide applications won't control the maggot, and might actually destroy the parasites that will go after the maggots later on."

Control options for the leafminer have changed little over the years. Leafminer activity was first documented in the early 1900s by entomologist W.J. Phillips. He observed that parasites were the most reliable form of control and that agriculturalists "need not concern ourselves seriously with remedies."

For more information about corn blotch leafminer, refer to the July 4 issue of the Purdue Pest & Crop Newsletter. The newsletter is available online.

Writer: Steve Leer, (765) 494-8415, sleer@purdue.edu

Source: John Obermeyer, (765) 494-4563, obe@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

 

Related Web site:
Purdue University Department of Entomology


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