Take-all of wheat
Take-all of wheat (Gaeumannomyces graminis var. avenae and tritici) occurs in temperate climates and can have a devastating effect. Plants with take-all initially have mild chlorosis, are stunted, and have poor tiller development. Around heading (FGS 10.5), patches of uneven, prematurely ripened wheat with white heads appear. Infected plants may eventually lodge. Roots are blackened while more severely infected plants have a black root crown, with blackening that extends up the stem. Black mycelia on the stem has a slight shine to it, and, if scraped off, small fungal fruiting bodies may be found underneath. This lower stem discoloration is diagnostic for take-all. Infected plants are typically easy to pull from the soil as they tend to have a depleted root system. Symptoms are most evident near heading and afterwards.
Wet weather and mild soil temperatures 40-60°F favor infection by the fungi that cause take-all. However, warm, dry weather later in the season favors symptom expression. Take-all tends to be more prevalent in soils that are neutral or alkaline (basic) soil, nutrient deficient, and poorly drained. Take-all is also more prevalent under irrigation.
Ensure proper soil fertility levels, particularly nitrogen, phosphorus, and manganese. Nitrogen in the form of nitrates may result in higher disease levels. Crop rotation with a non-host crop such as corn or a leguminous plant can be an effective management strategy. Kill volunteer hosts between seasons, as well as weed hosts that serve as a green bridge. Fungicide seed treatments can be used for early season protection against take-all. However, the causal pathogen can infect wheat after seed treatment effectiveness diminishes.
Gallery images: M. Burrows, C. Grau, E. Byamukama, and J. Marshall.