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Corn+Soybean Digest

Will Early Corn Planting Affect Insect Populations?

For every action, there is a reaction. With nearly 75% of the Illinois corn crop now planted, experts are discussing the potential reaction of insect populations to this year's early corn planting.

For several insects that migrate into Illinois each season, the severity of the infestation from year to year depends upon the intensity and timing of their migration flights. These insects include corn leaf aphids, corn earworms, black cutworms and fall armyworms.

Intense flights of black cutworm moths were reported in widely scattered areas throughout the state of Illinois from April 23 to April 26.

"Because the black cutworm's flight is so early in the growing season, it's easier to predict how early planting may affect potential outbreaks," says Mike Gray, University of Illinois Extension entomologist. "In general, early tillage and planting of corn works against the establishment of economic infestations of black cutworms. So, despite the recent intense flights across many areas of the state, I believe the prospects for widespread black cutworm problems this spring are low."

Because farmers removed weeds from fields this spring at a good pace, black cutworm establishment should be lower. Black cutworm moths will still lay eggs on crop residue, and they prefer soybean residue over corn. So first-year corn remains at greater risk to black cutworm injury than continuous corn.

Many insects overwinter each year in Illinois. In general, the early planting and establishment of corn root systems enhances the survival of root feeder insects such as the grape colaspis, western corn rootworm, white grub and wireworm.

However, Gray says the good growing conditions and warm soil temperatures should allow corn seedlings to grow more rapidly through susceptible seedling stages of development.

"For instance, cool and wet springs may slow corn seedling development sufficiently to enable insects such as wireworms and corn flea beetles to feed longer, causing more injury," he says.

Although western corn rootworm densities have been lower the last two seasons in Illinois, Gray suspects the early planting may result in larger densities of this perennial insect pest this season.

Early planting favors the establishment of the European corn borer's first generation, but due to the historically low overwintering population, Gray predicts this insect will not cause many problems this year in Illinois.

"It's important for producers to be vigilant with their scouting efforts now," Gray says.

For more information about the reaction of insects to early corn planting, read The Bulletin online.

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