As a follow-up to the article in the Bulletin (no. 21, August 25) "Wheat Diseases: Reflecting and Planning," the focus of this article is on winter wheat seed treatments. Although it's fairly easy to demonstrate improved stand establishment due to seed treatments, it does not necessarily translate into a statistical increase in yield. Even though both measures are valuable, obviously yield is more important. Table 2 illustrates a recent study of the performance of several wheat seed treatments. Which treatment(s) worked and which paid off in this study?|
Although all treatments significantly improved stand establishment compared to the check, only treatments 2, 3, and 5 provided a significant yield advantage (range of 5.3 to 6.2 bushels) in this study. Although treatment 4 was close, the difference in yield between it and the check (78.2 74.1 = 4.1) is not greater than the LSD value of 4.1, so technically there is no difference. (Practically speaking, in this case, most people would accept treatment 4 as equally effective anyway.) Sound crazy? To believe in statistics as a valuable and standardized evaluation tool, you must accept the fact that random variation exists. For example, yield for a particular variety will vary to some degree any time or place you test it. Some of this variation (for example, light, water, temperature, fertility, pests, and so on) can be accounted for in an experiment, but some variation (for example, due to genetics) will continue. Such variation makes it difficult to determine the real effects of a treatment, such as a seed treatment. Proper experimental design and statistical analysis provide a way to separate real effects from random variation and is the best way to avoid costly management errors.
Many variables come into play when deciding whether 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. For example, wheat grown for seed should be treated with a systemic fungicide such as carboxin, difenoconazole, tebuconazole, or triadimenol to control loose smut (an internal seed pathogen). Because many of these variables are difficult to predict with much accuracy before planting, most folks looking for "cheap insurance" either plant a little heavier or use an inexpensive seed treatment. Just like car insurance, you buy the coverage you need based on product performance, your particular situation, and desired comfort level.
As shown in Table 3 and Table 4, many different seed treatments are registered for use on wheat. As with most pesticides, each active ingredient has strengths and weaknesses, which is why combination fungicide seed treatments 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, septoria, 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 3. Table 4 lists some of the more common products used to treat wheat seed. This list is not complete and is given for illustrative purposes only. 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 only available to commercial seed treaters. Although many convenient combination products are already available, 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.
Remember how you've always been told if you're going to do a job, do it right? Yes, that advice applies here, too. Although we are not going to get into a debate over commercial versus on-farm seed treatment, suffice it to say that no matter who does the treating or how it is done you can't expect maximum benefit from the seed treatment when the product is not applied uniformly. A nonuniform application can outright kill some seeds, while leaving other seeds completely unprotected. On the other hand, in the quest for perfect coverage, you may cause excessive damage to the seed. As you can see, treating seed is a bit of a balancing act. Using the appropriate equipment in the first place can save you some frustration.
There are several on-farm, continuous-flow treating systems on the market. With the latter system, the liquid product is applied to seed as it passes through an auger from the bin or truck to the drills. For example, for a little more than $300, producers can purchase the F.A.S.T. (farmer-applied seed treater) system from Trace Chemicals (1-800-846-2980, or http://www.tracechemicals.com). If you use an air seeder, Flexi-Coil (http://www.flexicoil.com/rowcrop/aircarts/stu.htm) offers an optional, on-the-go seed treatment system with their air seeders. If you are considering an on-farm seed-treatment system this year, talk to your local equipment suppliers about the pros and cons of these and other seed-treatment systems, and any rebate offers that might be available to you.--Bruce Paulsrud and Wayne Pedersen