Factors associated with stem base and root diseases of New Zealand wheat and barley crops

Abstract

The incidence of stem base and root diseases of cereals in New Zealand was measured over a 3-year period to determine their relationships with soil and crop management factors. Samples were collected from 142 New Zealand wheat and barley crops during the milky ripe stage of crop growth and the proportion of tillers affected by stem base and root diseases in each crop was assessed. Take-all (caused by Gaeumannomyces graminis), and sharp eyespot (caused by Rhizoctonia cerealis) were common, whereas crown rot (caused by Fusarium spp.) was present at only low levels and eyespot (caused by Tapesia spp.) was not recorded. Incidence of both take-all and sharp eyespot was greater in wheat crops (mean of 8.3 and 12.6% tillers infected, respectively) than in barley (1.7 and 4.4%). Previous crop was the main factor associated with take-all in wheat crops. Incidence was highest where wheat followed wheat (mean of 29.3% tillers infected), and higher after barley, grass or clover than after other break crops. Although take-all incidence was high in most successive wheat crops, incidence was low (<20%) in a substantial proportion. A 1-year break from wheat was almost as effective as a longer break in reducing take-all levels in a subsequent wheat crop. Sowing month was the factor most closely associated with sharp eyespot incidence in wheat. Crops sown in early autumn had the highest incidence, whereas crops sown in winter and spring had only low levels of sharp eyespot. Several Fusarium species were associated with crown rot in wheat and barley. Fusarium avenaceum, F. crookwellense and F. culmorum were present in all regions, but F. pseudograminearum, F. semitectum and Microdochium nivale were more limited in distribution.