Effects of ploughing or direct drilling with three methods of straw disposal on amounts of inoculum of Pyrenophora teres, and on frequency of infection and severity of net blotch in the autumn, were studied in winter barley. Prior to ploughing, many conidia of P. teres were caught above areas where infected straw from a previous crop of winter barley had been bated and removed leaving culm bases, or where barley straw had been chopped and left in situ, but relatively few were caught above areas where straw had been burnt. Thereafter, where ploughing had buried surface residues, irrespective of the method of straw disposal, conidia were not caught for at least 3 weeks, and subsequently were substantially fewer than in direct-drilled areas where many spores were caught. Production of conidia (measured as numbers per unit length of straw) was greatest on chopped straw, less on culm bases and least on burnt straw residues. Sporulation on volunteer barley plants was much reduced by application of paraquat + diquat, but some still occurred on visually‘dead’volunteer barley.
All direct-drilled barley plants were diseased within 27 days of sowing, whereas 42 days elapsed before all plants sown in ploughed areas were diseased. Disease on individual plants was also more severe in direct-drilled areas: 20% of the area of the first leaf to emerge was diseased 19 days after crop emergence in direct-drilled plots, whereas less than 9% was diseased in ploughed areas 50 days after emergence.
There was an additive effect of straw disposal methods and direct-drilling on disease, which in turn affected plant vigour. The adverse effect of direct-drilling on the incidence and severity of net blotch appeared to be far greater than that of the straw disposal methods.