Originally published in Univ. of Illinois Pest Management & Crop Development Bulletin (31 May 1996)

Seed Treatments May be Reducing Stands
in Some Corn Fields

Photos by Bob Nielsen, Purdue University.

We have received several reports of less-than-acceptable plant populations in some fields of corn in western and southwestern Illinois. Although a reduced stand can be caused by a number of problems, the common denominator in the fields observed has been the application of a seed treatment, specifically Kernel Guard and, to a lesser extent, Agrox D-L Plus, at planting time. In several fields, apparently the kernels "tried" to germinate, but then they seemed to lose vigor. Frequently, the radicle was discolored. Also, some hybrids have been affected, others have not.

Both Kernel Guard and Agrox D-L Plus contain diazinon and lindane insecticides, in addition to captan, a fungicide. These seed treatments typically are used to protect the seed against a number of potential early season problems, including seedcorn beetles, seedcorn maggots, wireworms, damping-off, seedling blights, and seed decay.

The concentrations of diazinon and lindane are 15% and 25%, respectively, for both Kernel Guard and Agrox D-L Plus. Under normal growing conditions and for most corn hybrids, these insecticides are not phytotoxic. However, the Agrox D-L Plus label states: "Use only the recommended rate. Lower amounts may not give desired control. Excessive amounts may cause seed injury." (We could find no similar statement on the Kernel Guard label.) For most instances in which a stand reduction has been detected, higher-than-recommended rates were suspected. Slow germination and seedling growth in the cool, wet soils are not helping matters.

Although seed treatments containing diazinon and lindane are a cheap way to protect planted seeds against attack by seedcorn maggots and wireworms; the pesticide still must be used according to label instructions. The use rate for both seed treatments is one pouch per 50 pounds of seed, or 2 ounces per bushel. A typical recommendation is to fill the planter box half full, add one half the recommended rate of seed treatment, mix thoroughly; then add the remainder of the seed and seed treatment and mix again. Unfortunately, as some growers have discovered, not following label directions can result in problems. Replanting can be a costly operation.

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