Evaluation of fungicide efficacy and application frequency for the control of ascochyta blight in chickpea

Field experiments were conducted during 2002-2004 at Saskatoon, Swift Current and Kyle, Saskatchewan to assess the effect of application frequency, timing and rotation of different fungicides on the suppression of ascochyta blight, and on yield and seed quality of chickpea cultivars 'Myles', 'Sanford' and 'CDC Yuma'. Fungicides tested included chlorothalonil, azoxystrobin, pyraclostrobin, mancozeb and boscalid. Ascochyta blight severity ranged from 21 to 99% in untreated control plots and was significantly reduced through fungicide applications to levels below 25% in the most efficacious treatments. Increasing the number of fungicide applications was beneficial under high disease pressure, but was not always correlated with better ascochyta blight control. A pre-flower application had a positive effect by suppressing ascochyta blight severity, increasing seed yield or one-thousand seed weight in almost all experiments. Higher numbers of applications were not always correlated with higher seed yield and better seed quality. This may be due in part to poor yields in 2004 at Saskatoon and Kyle where above-average rainfall resulted in excessive vegetative growth. Different fungicide rotations had less of an impact on ascochyta blight management than the timing and the number of applications, but under moderate to high disease pressure, including strobilurin fungicides was beneficial. Five applications of mancozeb at two-week intervals were significantly less efficacious compared with rotations with other products.