Field Corn Soil Insect Management

Joanne Whalen, Extension IPM Specialist;

The following is a brief review of conditions favoring soil insects in field corn as well as observations from past seasons:

Corn Rootworm (Larval Control)
In general, rootworms continue to be more of a problem in continuous corn. Although generally more of a problem in heavier soils, we have also seen problems in continuous, irrigated corn fields planted in sandy soils. In our area, rotating out of corn is still a viable option for corn rootworm management. However, if you plan to plant continuous corn, control options include either a soil insecticide, a high rate of a commercially applied seed treatment, or a transgenic corn hybrid with resistance to rootworm larvae.

As far as seed treatments, reports from the Mid-West and areas in PA with heavy rootworm pressure state that “when rootworm densities and root injury have been low to moderate, seed treatments have provided acceptable protection of the roots. However, when rootworm densities have been high and root injury has been moderately high to severe, insecticidal seed treatments have not provided consistently acceptable control of corn rootworm larvae.”

High soil organic matter, sod covers, and heavy grass weed pressure the previous season all favor wireworm populations. In addition, damage from this insect is also higher in continuous corn. Commercially applied seed treatments i.e. Cruiser (thiamethoxam) and Poncho (clothianidin) have generally provided good wireworm control. NOTE – Labels for Cruiser and Poncho state seed and seedling protection.

In general, grubs are favored by a number of factors including planting into soybean stubble, old sod, hay, pasture, or set-aside acreage. Cruiser and Poncho are labeled against white grubs. Although these 2 chemicals can work against low to moderate grub populations, in the past few years we have seen poor control with both products in commercial fields under high pressure, especially when the predominant grub species has been Asiatic garden beetle. If populations are high, you may still need to consider an in-furrow application of an insecticide. NOTE – Labels for Cruiser and Poncho state seed and seedling protection.

Black Cutworm
This insect is favored by late planting, broadleaf weed growth (especially chickweed) present before planting, poorly drained field conditions and reduced tillage. Rescue treatments can be applied for this soil insect if you are able to scout fields twice a week once leaf feeding is detected. Pheromone traps placed in the field by mid-March can be used to determine when to look for cut plants. So far, we have not caught any black cutworms in our pheromone traps. Look for pheromone trap counts in future reports. If you are unable to scout and you have conditions favoring cutworms, one of the following preventive approaches can be considered: (1) a granular soil insecticide labeled for cutworm control applied as a t-band, or (2) a tank mix of an insecticide with a pre-emergence herbicide or (3) a Herculex corn hybrid. In general, the seed applied treatments (Cruiser and Poncho) have not provided effective cutworm control in our area, especially if economic levels of larger larvae are present at planting.

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