Take-All of Wheat and Barley
Take-All, caused by the fungus, Gaeumannomyces graminis var. tritici, occurs occasionally in Utah when wetter than average spring conditions prevail. Take-all affects wheat, barley, and rye as well as many other grasses in the Poaceae family. Wheat is the most susceptible to infection followed by barley, then rye whereas oats are resistant. Alkaline soils, which are common throughout Utah, are more conducive to take-all disease. It is also more destructive on irrigated grain.
Symptoms
Infected plants are stunted, mature early, and have white empty heads. In some cases, heads may not form at all. The base of the stem under the lower leaf sheath becomes covered with a coal-black fungal growth. The roots turn coal-black in color. Microscopic examination of the root reveals thick black runner hyphae.
Disease Cycle
G. graminis var. tritici survives saprophytically on stubble of cereals and on grasses. When a suitable host plant such as wheat or barley is planted into a field, the fungus moves via runner hyphae along roots and infects the host plant. The fungus grows on the surface of the roots and eventually a hyphal pad is produced. From this hyphal pad, an infection peg is produced which will penetrate the host tissue and allow the fungus to extract the nutrients it needs. Soil temperatures between 12-20°C (54-68°F) and saturated soils provide optimal growth conditions for the fungus. These conditions are normally prevalent in the late fall and mid-spring in Utah. Therefore, the date of planting is important.
Controls
Cultural controls
- Rotation is the best control for this disease. A 1-2 year rotation with corn, oats, or some dicots such as legumes is acceptable.
- Eliminate alternate grass and cereal hosts in the rotation. Volunteer wheat and barley will offset the benefits of rotation because the inoculum levels of the pathogen are not reduced.
- Till infected areas last to prevent spreading the disease organism to healthy areas of the field on equipment. Tilling helps to break down the stubble and promotes decomposition, which in turn will decrease inoculum build-up.
- Maintain fertility. Wheat and barley should never be stressed for nutrients. Ammonium- based nitrogen fertilizers can potentially reduce disease incidence. Nitrate fertilizers seem to enhance the disease incidence. Chloride fertilizers have been reported to decrease damage.
- Do not follow alfalfa that was heavily infested with cheatgrass, Bromus tectorum.
- Avoid planting wheat following wheat unless a long-term monoculture is planned. If a monoculture is desired, an initial drop in production may occur, usually lasting from 2-5 years. After this period, microorganisms that are antagonistic to the take-all fungus build up in the soil and disease incidence will be decreased.
- Early planted winter barley and wheat are most severely impacted since they are planted in soil conditions that are highly conducive to the pathogen.
Chemical Controls
Baytan or Dividend have shown marginal control of take-all.
Sherman V. Thomson/Extension Plant Pathologist
Scott C. Ockey/Plant Disease Diagnostician
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