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Issue No. 4, Article 1/April 29, 2010

What Impact Will the Early Corn Planting Have on Insect Populations This Season?

What a difference a year can make! The National Agricultural Statistics Service released a report (Adobe PDF) on April 26 that indicates 73% of the corn has been planted in Illinois as of April 25. This compares with 4% corn planting progress by April 25 last season and a five-year average of 28%. Even states farther north, such as Minnesota, have witnessed incredible progress to date, with 63% of corn planted by April 25. What impact will these early planting dates have on insect pests of corn?

For several insects that migrate into Illinois each season, the severity of the infestation from year to year depends on the intensity and timing of the flights. Insects in this category include corn leaf aphids, corn earworms, and fall armyworms.

Black cutworms also migrate into Illinois. Because their flight is so early in the growing season, it's a bit easier to offer a prediction of how the early planting may affect potential outbreaks. In general, early tillage and planting of corn works against the establishment of economic infestations of black cutworms. So, despite the recent intense flights (April 23-26) across many areas of the state, I believe the prospects for widespread black cutworm problems this spring are low. Removing weeds from fields this spring at such a good pace significantly reduced the chances for black cutworm survival. Black cutworm moths will still lay eggs on crop residue, and soybean residue is preferred to that of corn. So first-year corn remains at greater risk to black cutworm injury than continuous corn.

Many other insects overwinter each year in Illinois, including European corn borers, corn flea beetles, grape colaspis, western corn rootworms, white grubs, and wireworms. In general, the early planting and establishment of corn root systems will enhance the survival of root feeders, such as the grape colaspis, western corn rootworms, white grubs, and wireworms. However, 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. Western corn rootworm densities have been lower the last two seasons in Illinois. It will be interesting to see if the early planting results in larger densities of this perennial insect pest this season. I suspect this may happen. With regard to the European corn borer, early planting favors the establishment of the first generation. With the historically low overwintering population, this insect is still unlikely to cause much notice this year across Illinois.

Each year is different, and I look forward to your reports again this year. Thanks for sharing your field observations with me.--Mike Gray

Author:
Mike Gray

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