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Control of Soil-Inhabiting Insect Pests of Corn

March 20, 2003

For 2003, producers have many options for controlling soil-inhabiting insect pests of corn. The registration of liquid insecticides and insecticidal seed treatments has broadened the arsenal, and the more recent registration of YieldGard Rootworm corn (Monsanto's event MON 863 with the Bt Cry3Bb1 protein) has added yet another dimension to soil insect control in corn. (For more details, read the article about YieldGard Rootworm corn in this issue of the Bulletin.) With so many options available, an overview is in order.

Granular and liquid insecticides and insecticidal seed treatments currently labeled for control of corn rootworm larvae, cutworms, white grubs, and wireworms in Illinois are presented in Table 1. Note that all labels are not acknowledged for control. If a product label contains wording such as "suppression," "will aid in control of," or "reduces feeding" for any given insect, we have not acknowledged control in the table. For more information about a product (e.g., rate of application, placement, timing of application), read the label. You also can refer to Chapter 1, "Insect Pest Management for Field and Forage Crops," in the 2003 Illinois Agricultural Pest Management Handbook.

To limit the complexity of Table 1, we did not include other secondary soil-inhabiting insect pests of corn, such as grape colaspis, seedcorn beetles, and seedcorn maggot. Nor did we include insect pests that feed on corn seedlings above ground early in the season--billbugs, corn flea beetles, and southern corn leaf beetle. The latter usually can be controlled effectively with foliar-applied insecticides if scouting suggests that the insects are causing sufficient damage to warrant control. Nevertheless, several of the products listed in Table 1 include some of the aforementioned insects (both soil-inhabiting and aboveground insects) on their labels.

Some of the products in Table 1 are systemic (i.e., absorbed by treated plants and translocated from the site of uptake to other tissues). Such products may control both soil-inhabiting and aboveground insects early in the season. Insecticides with systemic activity include Counter, Cruiser, Gaucho, Prescribe, Regent, and Thimet. None of the other products listed in Table 1 are systemic.

Insecticidal seed treatments and liquid insecticides have become legitimate alternatives to granular soil insecticides. However, performance of seed treatments and liquid insecticides for control of corn rootworm larvae has not been as consistent as performance of Aztec, Counter, Force, and Lorsban in insecticide efficacy trials conducted in Illinois and Iowa. When infestations of corn rootworm larvae are high, seed treatments and liquid insecticides may not provide acceptable control. Efficacy data for the seed treatments and liquid insecticides against other soil-inhabiting insects in corn are not abundant. Some of the label claims are based on results from only a few research trials. Consequently, the effectiveness of these products against pests such as grape colaspis and white grubs is uncertain.

Remember that not all cornfields are infested with soil-inhabiting insects. Consequently, not all fields need to be treated with a granular or liquid insecticide or an insecticidal seed treatment. Producers should consider such factors as the history of insect pest problems in an area and in specific fields, the previous year's crop, the presence or absence of weeds, and planting time when deciding whether preventive control of soil-inhabiting insects is necessary. If a decision is made to apply a granular or liquid insecticide or an insecticidal seed treatment for control of soil-inhabiting insect pests in corn, determine which one or two pests are the primary targets for control, and decide among the available products accordingly. If you've had time to sort through data from insecticide efficacy trials, you also will have a better feel for which products provide the most consistent control of specific pests.

We intend to conduct numerous insecticide efficacy trials for control of soil-inhabiting insect pests of corn this spring, and we will apprise you of our results after we have evaluated the trials. Please don't hesitate to contact us if you want to tell us about soil-inhabiting insect pests of corn in your area this year. We are interested in learning as much as possible about effective or ineffective control of these pests.--Kevin Steffey and Mike Gray

Author: Mike Gray Kevin Steffey

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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