All wheat seed should be treated with a fungicide to control soilborne seed rots and seedling blights, seed-borne Stagonospora and Fusarium seedling blight, loose smut and bunt. No other chemical treatment provides a level of protection comparable to seed treatment for so little cost. Seed that has been cleaned to remove plant residue and lightweight kernels, then treated to achieve thorough coverage of the seed surface, will result in better final stands, especially if adverse weather conditions occur after planting. Lack of control of seedling blights may result in serious winterkill of diseased seedlings.
Diseases like Stagonospora glume blotch and Fusarium head scab, which occur on wheat heads late in the growing season, can severely affect the seed. Seed infection by fungi that cause these diseases causes shriveling, low test weight, and poor germination. Fungicide seed treatments should be used to control these fungi on seed to prevent stand losses in the fall (Table 2). Since Stagonospora nodorum survives over the winter on infected plants, preventing fall infection by planting treated seed will decrease the potential for Stagonospora leaf blotch in the spring (Figure 17).
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| Figure 17. Higher levels of Stagonospora on wheat seed result in higher levels of Stagonospora leaf blotch in the field. |
| Table 2. Effect of Fungicide Seed Treatment on Scab-Affected Wheat Seed. | |||
| Treatment | Fall Stand Plants/ft | Spring Stand Tillers/ft | Yield Bu/A |
| Raxil-Thiram | 25 a* | 55 a | 81.4 a |
| Dividend XL | 21 b | 56 a | 77.3 a |
| Untreated | 10 c | 33 b | 69.5 b |
| * Averages followed by the same letter within a column are not statistically different according to Fisher's least significant differences test at the 5% level of significance. | |||
Pythium is present in all agricultural soils, and disease development is favored by wet soil conditions soon after planting. Pythium damping off and seedling blight can be controlled with appropriate seed treatments.
The smut diseases, common bunt (Figure 18 and 19) and loose smut (Figure 20), have historically been responsible for major yield losses. However, since the development of effective seed treatments, their occurrence has been reduced to very low levels. The universal use of systemic fungicides would eliminate smut and bunt diseases as problems to wheat growers.
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| Figure 18. Common bunt was once the most devastating disease of wheat in Ohio. Widely spread florets and kernels converted to spore-bearing bunt balls are characteristic for this disease. Seed treatment is the only method for control. | Figure 19. Common bunt or stinking smut diseased kernels (bunt balls) containing spores. | Figure 20. Loose smut is recognized as heads first emerge from the boot. The florets are converted to black dusty spores that are blown away by the wind, leaving only a naked spike. Control is through the use of systemic seed treatments. |
No single fungicide will eliminate all seed and soilborne diseases. Therefore, a combination of an effective smut fungicide plus a fungicide effective against seedling blights is recommended. Several chemical companies have products containing combinations of fungicides effective against both seedling blights and smut diseases. These products are formulated for use in commercial treatment equipment or for use on the farm as planter box treatments. Labeling of seed treatment materials changes frequently. For information on seed treatment fungicides, consult the Ohio Field Crop Disease web site at www.oardc.ohio-state.edu/ohiofieldcropdisease.