Influence of Primary Weather Variables on Sorghum Leaf Blight Severity in Southern Africa

Abstract

A study was conducted on the effect of climatic factors (rainfall, min. and max. air temp.) on severity of leaf blight (Exserohilum turcicum [Setosphaeria turcica]) over several locations and years in southern Africa (Malawi, Swaziland, Tanzania, Zambia, Zimbabwe). The weather data used were from 2 weeks before sowing to 3 weeks after sowing. Temp. was the most important variable predicting disease severity after dough stage of the crop. High disease severities coincided with min. temp. between 14 and 16°C and mean temp. of 20.8-22.2°. Low severity at dough stage of the sorghum or absence of leaf blight was associated with min. temp. >16° from 2 weeks before sowing to 3 weeks after sowing. Discriminant analysis conducted using temp. from very early in the season correctly classified 88% of the cases into 3 disease severity categories: no, low and medium-high disease. It is concluded that, primary weather variables, in particular air temp., may be valuable predictors of disease severity early in the season. The results may be used to identify and map disease levels for large areas using past temp. data