EFFECT OF SOWING POINT DESIGN AND TILLAGE PRACTICE ON THE INCIDENCE OF RHIZOCTONIA ROOT-ROT, TAKE-ALL AND CEREAL CYST-NEMATODE IN WHEAT ANDBARLEY

Effect of tillage treatments on the cereal root diseases, rhizoctonia root rot, take-all and cereal cyst nematode, and on grain yield of cer eals were tested in 4 field experiments over 3 years. Conventionally c ultivated treatments were compared with a range of direct-drill treatm ents using either a standard tined seed drill equipped with 10 cm sowi ng points, a specialised drill designed to give minimal soil disturban ce or a standard tined seed drill equipped with a range of commercial or modified narrow points designed to provide soil disturbance from 0 to 5.0 cm below seed depth. Direct-drilled treatments that disturbed t he soil below seed depth (DDD) and treatments that included 1 cultivat ion prior to sowing (CPS) resulted in a reduction of rhizoctonia root rot when compared with direct-drilled treatments that did not disturb the soil below seed depth (DDN). When seasonal conditions encouraged v olunteer plant growth before sowing, a chemical fallow treatment appli ed 3 weeks before sowing significantly reduced rhizoctonia root rot in all direct-drilled plots. This was a significant factor in DDD treatm ents providing effective control of rhizoctonia root rot. Take-all was present in 3 of the 4 experiments. In 2 experiments, take-all was sig nificantly higher in plots following DDN treatments than DDD or CPS tr eatments and in 1 experiment there was no effect of tillage. Cereal cy st nematode was present in 1 of the 4 experiments. The level of root d amage from cereal cyst nematode was least in plots following DDN treat ments, higher following DDD treatments and highest following CPS treat ments. The influence of tillage practice on grain yield was closely re lated to the effect of tillage on cereal root disease when levels of d isease were moderate to high. Where the incidence of root disease was low, grain yield differences due to tillage treatments were generally related to agronomic factors such as seed depth and seedbed condition.