Gaeumannomyces graminis var. tritici attacks wheat, barley, rye and may attack some grass species, particularly couch grass (Elymus repens). Oats are immune.
Gaeumannomyces graminis var. avenae attacks oats, wheat, barley, rye and many grass species.
The take-all fungus attacks the roots of plants as it is soil-borne. If diseased plants are pulled up, the roots can be seen to be blackened and rotten and have a "rat-tail" appearance. In severe outbreaks the base of infected plants may also show blackening. Above ground symptoms are seen as patches of stunted plants and white-heads ("bleached" ears) in mature plants. White-heads generally contain small grains or, occasionally, no grain at all.
Take-all survives the winter primarily as mycelium on roots or stubble debris, volunteer cereals, early autumn-sown crops and some grass weeds. Primary infection occurs in autumn from inoculums in the soil. Secondary (root-to-root) infection occurs mostly in spring and summer. The disease spreads from infected seedling roots to developing crown roots. 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 white-heads and often poor grain filling.
Take-all is arguably the most important disease of wheat in the UK, partly because it is not easily controlled chemically or by varietal resistance 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 wheat. Grain from plants showing white-heads are usually small and shriveled. 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 (take-all decline).
Most employ cultural control of take-all by ensuring a sensible crop rotation. A one year break from susceptible crops will usually prevent the disease causing problems in the subsequent cereal crop. Early drilled crops are particularly prone to severe disease attacks. It is therefore advisable to sow first wheat crops first, long-term wheat next and second and third wheat last. Seedbeds should be well consolidated and fields well drained with good soil structure, particularly in light soils. Volunteers and grass weeds should be controlled to prevent carry-over of the disease when non cereal crops are grown. If successive cereal crops are grown take-all will generally build up during the second or third years. However, take-all will almost invariably decline during subsequent years until it reaches a stable position when yields are acceptable. The yields of long term cereals where take-all decline is established are never as high as those of first wheat but may allow the crop to continue to be grown economically. If a run of continuous cereals is broken by a non-susceptible crop, the process of take-all decline will be repeated in subsequent cereal crops. A set-aside break is usually not sufficient to destroy the take-all decline position and cereals can often be re-introduced without suffering yield loss.
Disease resistance in wheat, barley and oats to the respective subspecies of G. graminis is low. However, G. graminis var. avenae is not widespread in the UK and in most areas it is possible to exploit the resistance of oats to take-all and use the crop as a break crop in a rotation. There is some evidence of good levels of resistance in some triticale varieties.