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Causal organism - Gaeumannomyces graminis
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Take-all survives the winter primarily as mycelium on roots or stubble debris. Volunteer cereals, early autumn-sown crops and some rhizomatous grass weeds may also act as overwintering sources of inoculum . The main infections of cereal roots occur from late May onwards in the UK when temperatures exceed 10°C. However, autumn infection occurs commonly in early-sown crops when weather conditions are mild. As the disease progresses during the season, the root area lost to the disease increases and the ability of the plant to absorb water and nutrients from the soil declines. When root rotting is severe plants are unable to absorb water and nutrients. As a result the plants ripen prematurely, resulting in whiteheads.
Take-all is arguably the most important disease of wheat in the UK, partly because it cannot be fully controlled chemically and relies on rotational strategies for control. Even on chalky boulder clay soil losses of 10-20% are common in second and third wheat crops. On less well bodied soils yield losses can be much higher or indeed it may be impossible to grow second or subsequent wheats. Grain from plants showing whiteheads is usually small and shrivelled or, in severe attacks, there may be no grain present in the ear. Take-all causes most damage on light soils, particularly if they are alkaline in nature. Severe attacks can also occur in acid patches. Poor drainage and nutrient status also encourage the disease. Take-all is particularly encouraged by early sowing and light, puffy seedbeds. The disease is usually most severe in the third or fourth successive cereal crop, but generally declines in importance in continuous cereals.
