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Planting disease-resistant varieties is the most economical and effective method of controlling diseases. Cost of the seed is the same whether the variety is resistant or susceptible. One should study information on disease reactions available from university variety evaluation tests. Varieties should be selected based on disease resistance, yield potential, maturity date, straw strength, and winter hardiness. This is especially important where disease problems have been encountered in the past. Information on varietal reactions to disease can be viewed on the Ohio Field Crop Disease web site at www.oardc.ohio-state.edu/ohiofieldcropdisease. Varieties with effective levels of resistance to leaf rust (Figure 1), powdery mildew (Figure 2), Septoria tritici leaf blotch and Stagono-spora nodorum leaf and glume blotch (Figures 3 and 4), Stagono-spora nodorum (Figures 5 and 6), and wheat spindle streak mosaic virus (Figures 7 and 8) are available. Varieties with a moderate to high level of resistance will usually prevent yield losses under normal conditions (Table 1). However, when new races of a pathogen develop that attack previously resistant varie-ties, or when weather conditions favor early development and spread of certain pathogens, yield losses can occur. Varie-ties may have a high level of resistance to one or possibly two diseases, but rarely more. Choose varieties with resistance to the one or two most prevalent diseases in your area. |
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Figure 1. Small, oval, reddish-orange pustules are characteristic of leaf rust. Severe yield losses can result when as little as 3 to 5% of the flag leaf becomes infected by flowering of the wheat plant. | |
Figure 2. Powdery mildew is easily recognized by the white-powdery mold growth on leaf surfaces. Powdery mildew is one of the most prevalent wheat diseases in the state. |
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Figure 3. Septoria tritici leaf blotch (left) and Stagonospora nodorum leaf blotch (right) can cause serious yield losses during seasons with long periods of wet weather. | |
Figure 4. Septoria tritici leaf blotch is one of the earliest diseases to affect wheat in the spring. It can be recognized as oval to irregular spots or blotches with ash gray centers and the presence of black fungal bodies speckled over the lesion surface. |
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Figure 5. Stagonospora nodorum leaf blotch is more common in June. Lesions are oval with chocolate brown centers frequently with brown borders and a yellow margin. | |
Figure 6. Stagonospora nodorum glume blotch can be recognized on the florets of the wheat head. Generally, disease begins at the glume tip then advances downward to the glume base. Stagonospora nodorum can infect the kernels, causing shriveling and poor germination. |
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Figure 7. Wheat spindle streak mosaic is one of the most common virus diseases on wheat in Ohio. The light yellow spindle shaped spots on the leaves are characteristic of this soilborne virus disease. | |
Figure 8. Varieties that are susceptible (left) and resistant (right) to wheat spindle streak mosaic. |