BROWN LEAF-SPOT DISEASE AND FERTILIZER INTERACTION IN IRRIGATED RICE GROWING ON DIFFERENT SOIL TYPES

Studies have been undertaken in a 1000 ha area of irrigated rice (Oryz ica sativa) at Caroni (1975) Limited to determine the effect of the fe rtilizer programme on-the incidence of important diseases. Over a peri od of three years higher levels of brown leaf spot (Cochliobolus miyab eanus) on rice varieties Oryzica 1 and Oryzica 5 on three different so il types were associated with increasing levels of leaf P, from a low of 0.149% of dry matter (DM) to a high of 0.396% DM. On the Washington silty clay loam series (Inceptisol) brown leaf spot incidence was low est when leaf P was between 0.135% and 0.149% of DM. However, disease incidence was higher when leaf P levels fell to 0.133% of DM or rose a bove 0.149%, under conditions where N was more than adequate. The mode rate levels of the disease experienced over the period had no effect o n yield, as grain infection was minimal. The results support the concl usion that the incidence of brown leaf spot on irrigated rice at Caron i is influenced by sub-optimal levels paticularly of P. Careful monito ring and managememt of P nutrition is seen as an important part in the overall strategy for controlling the disease.