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Wheat (Triticum aestivum) - Take-all
Cause A fungus, Gaeumannomyces graminis var. tritici, which lives in soil or diseased grass stubble. Grass seed fields are seriously affected in western Oregon and Washington, especially during wet years in fields with a heavy straw load.
Infections is favored by soil at 50°F to 68°F and moist conditions. The severity of infection by flowering, soil moisture levels after flowering, and fertility program all strongly influence yield losses. Liming of moderately acidic soils increases disease incidence.
Symptoms The stem's base is covered with a coal-black fungal growth under leaf sheaths. Individual roots turn coal black and are coal black on the interior when scraped. Plants are stunted, mature early, and have white, empty heads. Some tillers may fail to head.
Cultural control
- Crop rotation with at least one year out of grass or wheat is very effective at reducing the pathogen population. Vegetables, corn, annual legumes, and oilseed crops are non-hosts.
- Bury grassy debris to ensure breakdown of infected plant residues.
- Maintain good nitrogen levels. Using ammonia forms of nitrogen and chloride fertilizers lessen yield losses when soil pH is near 5.5. When soil pH is 5.2 or less, liming can aid, especially when low phosphorus (P) levels prevail.