DECLINE IN ROOT-ROT (RHIZOCTONIA-SOLANI AG-8) IN WHEAT IN A TILLAGE AND ROTATION EXPERIMENT AT AVON, SOUTH AUSTRALIA

Studies of a tillage x rotation field experiment begun in 1978 at Avon , South Australia, have demonstrated a decline in rhizoctonia root rot of wheat. In direct-drilled treatments the severity of rhizoctonia ro ot rot culminated in 1983, with patches of poor plant growth accountin g for up to 46% of the crop area, and then declined to negligible leve ls by 1990. Disease severity was significantly less in cultivated than direct-drilled treatments. In cultivated treatments the onset of decl ine was more difficult to determine, but by 1990 there was negligible rhizoctonia root rot in either tillage treatment, with no increase in disease from 1990 to 1994. Decline in rhizoctonia root rot occurred la rgely independent of rotation, although there were significant differe nces in root damage and patch area between rotations, with disease gen erally being more severe in wheat following pasture than following pea s, medic, or wheat. When inoculum of R. solani was added to soil colle cted from the experimental site in 1985, wheat grown in soil from dire ct-drilled plots had significantly less disease than wheat grown in so il from cultivated treatments, indicating a possible development of su ppression.