Planter Box Seed Treatments

During 1996, Extension Entomologists at Purdue University and the University of Illinois reported corn stand loss from use of planter box seed treatment. In Wisconsin, we frequently use such compounds on first year corn, and because of this, I am enclosing the following article by John Obermeyer, Rich Edwards, and Larry Bledsoe, as it appeared in the 14 March 1997 Purdue newsletter.

For years, entomologists have advocated the use of seed treatments containing the insecticides diazinon and lindane for protection of seed against seed-attacking insects. It is recognized that the longer germination is delayed, the greater the chance that seedcorn maggot, seedcorn beetle, and/or wireworm damage may occur. As producers plant earlier and into greater levels of crop residue that keeps soils cooler and more moist, the small price for a seed treatment that protects slowly germinating seeds seems a wise investment.

Three-way seed treatment combinations containing diazinon, lindane, and the fungicide captan (Agrox D-L+, Kernel Guard, and KickStart) have been used for over 15 years. Occasionally it is reported that phytotoxicity/emergence problems result when a three-way seed treatment is used. Normally it is the lindane component of the mix that creates the problem. Patterns of damage in fields indicate that where the planter was refilled with seed and the seed treatment that a portion that did not stick to the seeds filtered into the planter fingers. This resulted in an over-application of the product for a portion of the field. Attempts to duplicate this damage have often failed, suggesting that specific growing conditions rather than seed genetics dictate seedling phytotoxicity. Ironically, cool and wet soils coupled with early planting, where one would likely see the benefit of this treatment, is also when most phytotoxicity occurs.

The year 1996 will go down in the record books as one of the coolest and wettest of the twentieth century. Some seed that was planted in April 1996 sat in the soil over three weeks before germinating and emerging. Even though these conditions created the perfect scenario for the use of a seed treatment, there were some fields that sustained considerable stand loss due to phytotoxicity. Follow-up investigations on these fields revealed that producers were using the "rule of thumb" rate of one pouch per bag of seed. However, the label reads "use at a rate of one pouch per 50 pounds of seed (2 ounces per bushel)." Bagged seed corn often weighs considerably less than 50 pounds, therefore the producers unknowingly were over-applying the seed treatment. As with other pesticides, crop injury can occur when a product is used at higher than label rates, especially in such harsh spring conditions. In response to the damage that occurred last year, Trace Chemical (manufacturer of Kernel Guard), has changed their packaging to better reflect the seed industries weight of bagged seed corn.

We continue to recommend the use of these 3-way seed treatments when planting into cool, wet soils where there are high rates of crop residue and/or manure applied. When used at labeled rates, these seed treatments should provide good protection against seedcorn maggot and seedcorn beetle. Against low levels of wireworms, lindane will give some protection. However, one must recognize the weakness of these seed treatments; that is, once the kernel sprouts, there is little to no protection. Also, a seed treatment will not provide control against white grubs and rootworms or high populations of wireworms.

A seed treatment containing diazinon can no longer be used on SOYBEAN. This change has occurred since last season. Do not use Agrox D-L+, Kernel Guard, or KickStart on soybean. Lindane is still legal to use. However, there are a limited number of products available with the combination of lindane and captan.