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Results from a series of crop sequence and single-year experiments that tested different straw and cultivation treatments in a total of 11 site–season combinations confirmed previous evidence that the development of eyespot disease in cereals can be decreased by debris in the seed bed even if that debris includes eyespot-infected stem bases, which are the principal sources of primary inoculum. Two of the experiments, which followed non-cereal break crops and tested the effects of crop debris applied after ploughing or tining on eyespot in winter wheat that was artificially inoculated with Oculimacula spp., provided convincing evidence that the effects can be attributed to the debris per se, and not to any associated husbandry practices. There were often larger effects on disease in summer than in spring or on severity than on incidence suggesting that the effects of debris cannot be explained solely by effects on inoculum or initial infection, and that debris has a disease-suppressive effect. [ABSTRACT FROM AUTHOR]

Three separate experiments showed that wheat tissue infected with the cereal eyespot fungus, Pseudocercosporella herpotrichoides, produced fewer spores in the presence of chopped wheat straw than when it was absent. This provides a possible explanation for earlier observations that there was often less eyespot in plots where straw had been incorporated than where it had been burnt. Sporulation on eyespot infected wheat tissue was not closely correlated with the viability of P. herpotrichoides, which could usually be isolated from infected tissue for some time after it had apparently lost the ability to produce spores. Many of the colonies that were isolated from such tissue also failed to sporulate under the conditions used but non sporulating colonies were less common amongst those isolated from tissue that had been mixed with chopped straw than from tissue that had not. [ABSTRACT FROM AUTHOR]

Fungicides, applied to control powdery mildew (Erysiphe cruciferarum Opiz ex L. Junell) on swedes (Brassica napus L. var. napobrassica Peterm), increased root yield by up to 66, 57 and 45 per cent in 1974, 1975 and 1976 respectively. In 1975, early-sown swedes yielded more than late-sown swedes when sprayed to control mildew. Untreated swedes gave similar yields whether sown early or late. Early sowing also increased the incidence of virus diseases. Insecticide sprays decreased aphid numbers but had little effect on virus incidence; they significantly increased root yield when tested in 1975 but not in 1976. [ABSTRACT FROM AUTHOR]

In field experiments with winter wheat in Hertfordshire, seed infection with Septoria nodorum and the incorporation of infected straw into seedbeds were often correlated with reduced seedling establishment and increased seedling infection. Artificially infected straw was a less effective source of inoculum than naturally infected straw, which gave rise to the most severe leaf symptoms in one season when heavy rain favoured the development of an epidemic. In an experiment where a severe epidemic did not develop, organomercury seed treatment was the most important factor increasing seedling emergence and grain yield, also apparently leading to decreased Septoria infection of the flag leaf sheath. Spores from lesions which developed after plots were sprayed with a suspension of pycnidiospores of S. nodorum were not always morphologically typical of that species. [ABSTRACT FROM AUTHOR]

Mildew on winter cereals in autumn was increased by early sowing and proximity to infected plots sown earlier but, in all years, very little could be detected during late winter and early spring, even where there had been much in autumn. Differences in amounts of autumn mildew between plots, whether due to different sowing dates or proximity to areas of differently treated stubble, did not persist beyond spring, and in summer there was usually most mildew on, those crops sown late which had earlier been least infected. [ABSTRACT FROM AUTHOR]