Take-all

"Gaeumannomyces graminis" var "tritici", syn. "Ophiobolus graminis" var "tritici"

A disease of cereal roots common in temperate climates. All varieties of wheat and barley are susceptible. It is an important disease in winter wheat in Western Europe particularly, and is favoured by conditions of intensive production and exacerbated by monoculture.

The fungus attacks the plant roots at any growth stage, early infections causing stunting and yellowing. Affected roots are blackened, sometimes severely. After earing in spring patches of the crop appear stunted. In severe attacks the worst affected plants are bleached and dead even before flowering. These symptoms give rise to an alternative name for the disease, "whiteheads". Yield loss levels of 40 to 50 % are often recorded in severe attacks.

Chemical control measures have traditionally had little success, although a modern seed treatment shows promise. Crop nutrition imbalances exacerbate the disease, as does excessive liming. Modern varieties are stiff and short-strawed which allows relatively high spring nitrogen applications without serious lodging. This can limit damage from the disease.

The most appropriate control measure is the use of a clean one-year break crop of a non-cereal crop. This reduces the fungus to an acceptably low soil contamination level in about 10 months although the existence of volunteer grasses may nullify any beneficial effects.

There exists a phenomenon known as "take-all decline". Experiments performed on the famous "Broadbalk" field at Rothamsted Experimental Station where continuous monoculture winter wheat is grown, show that take-all build-up occurs in successive crops to reach a peak in the 3rd to 5th cropping year, after which the disease declines, ultimately restoring yields to 80 to 90 % of 1st and 2nd year levels. The decline cycle is destroyed by the introduction of a crop other than wheat or barley.

References

Cereal Pests and Diseases (Gair, Jenkins, Lester) 1987 Farming Press ISBN 978-0-85236-164-1