Effects of rotation, stubble retention and cultivation on take-all and eyespot of wheat in northeastern Victoria, Australia

Abstract

The effects of different rotations and methods of seed-bed preparation on take-all ( Gaeumannomyces graminis var. tritici) ( Ggt) and eyespot ( Tapesia yallundae; anomorph Pseudocercosporella herpotrichoides) of wheat ( Triticum aestivum) were investigated in 1984–1986 in a long-term field experiment (established in 1981), on a fine sandy-clay loam in northeastern Victoria. One treatment, representing the conventional practice, involved burning stubble from the preceding crop followed by four passes with a scarifier in the autumn before sowing wheat each year. Other treatments were direct drilled each year (sown without prior cultivation) and included two stubble treatments (retained or burnt) in either continuously cropped wheat or in lupin ( Lupinus angustifolius)-wheat rotations. High levels of take-all and eyespot developed in the continuously cropped wheat (up to 79% and 66% plants affected, respectively). On the other hand, the incidence of plants with either disease was very low or negligible in wheat that was preceded by lupins. In continuous wheat the incidence of plants with Ggt lesions were up to two times higher in the conventionally cultivated treatment (14% 74% and 79% plants affected in 1984, 1985 and 1986, respectively) than in direct drilled treatment (5%, 36% and 39% plants affected, respectively). Generally, the incidence of plants with Ggt lesions and the severity of root symptoms in direct drilled wheat did not differ significantly between the two stubble treatments. The incidence of eyespot in direct drilled wheat was exacerbated by the retention of wheat stubble on the uncultivated plots (3%, 46% and 66% plants affected in 1984, 1985, and 1986, respectively) but was reduced by burning the stubble (4%, 19% and 33% plants affected in 1984, 1985, 1986, respectively). However, cultivating soil after burning stubble resulted in more plants with eyespot (14%, 39% and 46% plants affected in 1984, 1985 and 1986, respectively) than did burning stubble alone, and in one year the incidence of affected plants in the cultivated treatment was as high as in wheat direct drilled into stubble. The incidence of eyespot was positively correlated ( r=0.85, 0.84 and 0.61 in 1984, 1985 and 1986, respectively) with the incidence of lodged tillers. The incidence of lodging was, generally, highest each year in wheat sown directly into wheat stubble and was reduced by burning wheat stubble or by cropping wheat after lupins. Wojnowicia graminis was frequently isolated, as was Tapesia yallundae, from eyespot lesions suggesting that perhaps not all symptoms of lodging in Victoria can be attributed to Tapesia yallundae.