Figure 1. Severe Fusarium head blight in a grower's field in Saunders County on June 19, 2015. Grain from a field like this will be Fusarium-infected and should be cleaned and treated with a systemic fungicide if it is to be used as seed for the next wheat crop.
July 24, 2015
Fungicide seed treatments help reduce losses caused by seed-transmitted and soilborne fungal diseases of wheat. Some seed treatment products contain a fungicide and an insecticide and offer additional protection against fall insects such as aphids.
Figure 2. Bunt balls (spore-filled grain) containing spore masses of the common bunt (stinking smut) fungus.
Figure 3. Loose smut. Spores of the fungus replace grain on the wheat head.
Figure 4. Black point. The disease is caused by several fungi during grain maturation. The fungi blacken the embryo end of the grain.
This year it will be especially important to use fungicide-treated seed because there were widespread epidemics of Fusarium head blight, also known as scab (Figure 1). The scab fungus infects and stays in the grain, resulting in shriveled, chalky white or pinkish kernels known as Fusarium-damaged kernels, scabby kernels, or "tombstones." Kernels infected in later stages of development contain the fungus but look normal. If Fusarium-infected grain is not treated with a fungicide and is used as seed for the next crop, stand establishment can be significantly reduced.
Another reason why it is important to use fungicide-treated seed this year is that flag smut, a rare seed transmitted disease that can cause significant yield loss if severe and widespread, was found in several counties in Kansas, including counties close to the Nebraska border. Some countries will not import wheat from countries or states that have flag smut. Therefore, the economic implications of flag smut can be significant at a state or regional level.
Seed-Transmitted Diseases
Figure 5. Ergot. Individual seeds on the wheat head are replaced by black sclerotia or ergots (compact masses of mycelium of the causal fungus).
Figure 6. Scabby wheat with kernels infected by the scab (Fusarium head blight) fungus. Severe seedling blight can result if this grain is used as seed.
Seed-transmitted fungal diseases of wheat include common bunt, also known as stinking smut (Figure 2); loose smut (Figure 3), flag smut, black point (Figure 4), ergot (Figure 5) and diseases caused by Fusarium (Figure 6). These diseases can cause varying levels of yield loss and occasionally total loss.
Loss results from seedling blights and damping off caused by some of the causal fungi and grain loss caused by common bunt and loose smut fungi. In the case of common bunt, if it is widespread in a field, total loss is almost certain due to rejection at the elevator.
In addition to loss in quantity, these diseases also lower grain quality and therefore value because affected grain is downgraded.
Soilborne Diseases
Figure 7. Poor stand establishment due to soilborne and some seed-transmitted diseases of wheat.
Soilborne fungal diseases of wheat include common root rot, Pythium root rot, Rhizoctonia root rot, and Fusarium root, crown, and foot rots. These diseases often go unnoticed because they affect the roots and crowns and therefore are not as visible as foliar diseases. However, they cause significant yield loss resulting from poor stand establishment (Figure 7) and weakened plants that are vulnerable to attack by other diseases and insects.
Management
Seed-transmitted and soilborne fungal diseases of wheat are effectively controlled by planting certified, fungicide-treated seed. Because some of these diseases are internally seedborne, systemic fungicides are recommended. Avoid planting farm-saved seed from previous years.
Treating Seed
It is best to buy certified treated seed or use a commercial seed conditioner to clean and treat seed. Seed treated on-farm should be cleaned before treatment. Thorough coverage maximizes effectiveness of the seed treatment. For a list of seed treatment fungicides for control of seed transmitted and soilborne diseases of wheat, see Table 1 (updated 7/30).
Stephen Wegulo Extension Plant Pathologist
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