Many variables come into play when deciding whether or not seed treatments pay off, including seed cost, seed treatment cost, crop value, seed condition, seed bed condition, time of planting, anticipated disease and insect pressure, intended crop use, and options for disposal of excess treated seed. Because many of these variables are difficult to predict with much accuracy before planting, most folks looking for "cheap insurance" either plant wheat a little heavier or use an inexpensive seed treatment. Just like car insurance, you buy the coverage you need based on product performance and your particular situation and desired comfort level.
There are many different seed treatments registered for use on wheat. As with most pesticides, each active ingredient has strengths and weaknesses, which is why premixed fungicide products are so common. In addition, an insecticide may be included or used alone to control insect pests. Typically, seed treatments will last only about 10 to 14 days beyond planting. However, certain active ingredients can protect the seedlings considerably longer when applied at the highest labeled rate. For example, difenoconazole and triadimenol can protect against fall-season foliar disease such as powdery mildew and rust. In addition, imidacloprid may be included or used alone to control aphids that transmit the barley yellow dwarf virus. Although these long-lasting systemics offer a good deal of protection, they are relatively expensive.
Common seed treatment active ingredients and the fungi they control are listed in Table 5. Table 6 provides a current, but likely incomplete, list of seed treatment pesticides labeled for treating wheat seed. Check with local dealers to determine what products are available in your area and at what cost. Also, consult the Illinois Agricultural Pest Management Handbook for further information. Several of these products are available only to commercial seed treaters. Although there are many convenient premix products in the market, should you decide to create your own combination, be sure to read and follow the labels of each product and contact the manufacturer(s) if you need clarification.
To learn more about the biology of seed and seedling pests, consider purchasing the current Field Crop Scouting Manual, available at your local University of Illinois Extension office. For a comprehensive seed treatment resource, consider purchasing Illinois Pesticide Applicator Training Manual: Seed Treatment (SP 39-4), also available through University of Illinois Extension. The seed treatment manual was revised in November 2001 and addresses common seed and seedling pests, seed treatment active ingredients, safety issues, and seed treating equipment and calibration.--Bruce Paulsrud and Wayne Pedersen