EFFECTS OF SOWING WINTER BARLEY ON DIFFERENT DATES IN AUTUMN ON THE SEVERITY OF TAKE-ALL (GAEUMANNOMYCES-GRAMINIS VAR TRITICI) IN THOSE AND THE SUBSEQUENT CROPS

Experiments on winter barley at Rothamsted, testing different sowing dates, were sampled in 1987-89 to measure effects on take-all caused by the fungus Gaeumannomyces graminis var. tritici. The experiments used the same plots in each year, and in 1988 and 1989 the randomization was restricted so that sowing dates were balanced for sowing dates in the previous year. The site had been used to grow barley since at least 1979 (spring barley from 1979 until 1985), and take-all was much more severe than expected. It was usually most severe in the earliest-sown plots and decreased almost linearly as sowing was delayed. There was also evidence that the sowing dates of the preceding crop had a continuing, residual effect. In the two years that the effects of previous sowing dates were tested, there was usually least take-all in plots where the crop followed one sown very early or very late in the previous year, and most where it followed one sown at the end of September or in early October. These effects probably reflect differences in amounts of inoculum and in the rate of development of take-all decline.