Variations in Cereal Yield Losses associated with Heterodera avenae in England and Wales1

Many field experiments in England and Wales during the past 20 years have measured cereal yield losses and established regressions of yield on numbers of Heterodera avenae. Yield benefits from soil sterilants were greatest where most H avenae was present. Isogenic selections of barley and oats resistant and susceptible to H. avenae were extensively grown to assess the losses caused by this nematode alone. In some experiments these losses were identical with those measured by nematicide use, but in others (notably where broad spectrum biocides were used) losses were greater than those attributable to H. avenae and could be explained only by the known incidence of accompanying pathogens. Some yield loss may be due to migratory nematodes, e.g. Pratylenchus spp. occurring with H. avenae. Barley and wheat yields in the last 30 years have increased by 63 and 84 % due to improvements in cultivars and farming practice. Smaller percentage loss in a high yielding crop can be as costly as large percentage loss in poor crops grown on dry light soils. Many factors - soil type, rainfall, nutrients, other pathogens etc. - can greatly modify crop responses to similar popuiation levels of H. avenae.