Effect of short chemical fallow on Rhizoctonia bare patch and root rot of wheat at Esperance, Western Australia

Abstract

The effects of short chemical fallows after ryegrass pasture on rhizoctonia bare patch and root rot ofwheat were studied in 2 experiments at the Esperance Downs Research Station, 35 km north of Esperance, W.A. In 1 experiment the subterranean-clover dominant pasture was sprayed with a paraquat-diquat mixture prior to resowing with annual ryegrass at densities ranging from 3 to about 400 plants m-2. The ryegrass was allowed to grow for either 42 or 63 days prior to treatment with a desiccant herbicide (paraquat-diquat) followed by a short chemical fallow of 26 or 5 days, respectively, before sowing with wheat using minimum tillage. Some treatments were cultivated twice to 10 cm. Neither the ryegrass density nor the length of chemical fallow had any effect (P=0.05) on rhizoctonia bare patch score or incidence or severity of root rot. However, cultivation caused 76% reduction in mean patch score and a 38 and 68% reduction in mean rhizoctonia incidence and severity respectively. Yield was negatively correlated with rhizoctonia incidence and severity: each 1% increase in incidence percentage resulted in 17 kg ha-1 reduction in grain yield of wheat. In another experiment, chemical fallow periods of 66, 52, 24 or 1 day prior to sowing wheat had no effect (P= 0.05) on rhizoctonia root rot incidence.