Take‐all in spring‐sown cereals under continuous cultivation: disease progress and decline in relation to crop succession and nitrogen

SUMMARY Incidence and severity of the take‐all disease in spring wheat and spring barley caused by Gaeumannomyces graminis (syn. Ophiobolus graminis ) were studied during seven years of monoculture. The fungus apparently survived for much longer periods in the soil under non‐susceptible break‐crops than previously recorded. The incidence and severity of infection increased progressively with each successive cereal crop from initially low levels to a maximum within 3–7 years, which was followed by a progressive but limited decline in the disease. Spring wheat was more susceptible to take‐all than spring barley and the development of take‐all decline (TAD) was recorded earlier in the sequences of wheat than of barley crops. Nitrogen did not influence the disease until the point of maximum incidence and severity, when it caused a reduction in disease levels in addition to that associated with TAD. Factors influencing the time of onset and the rate of development of take‐all and of TAD are discussed and possible explanations for TAD are suggested.