Fungal mycelia and sclerotia in the soil. Or use split nitrogen applications. Click on an image to display it in larger detail. Gaeumannomyces graminis var. Infected plants appear mildly chlorotic and have fewer tillers.
Roots are few, black, and brittle.
More severe where wheat follows wheat or with no-till. Tolerant cultivars, crop rotation. Avoid planting before the fly-free date. Avoid nitrogen stress. Add ammonia or slow-release forms of nitrogen in fall.