Management strategies for Alternaria leaf spot of soybean (Glycine max) caused by Alternaria alternata

Abstract

Alternaria leaf spot disease caused by Alternaria alternata is one of the most economically important disease insoybean production. Efficacy of four fungicides and two botanical formulations were tested against six isolates ofA. alternata collected from major soybean [Glycine max (L.) Merr] growing areas of Rajasthan during rainy (kharif)season 2018 and 2019 at Department of Plant Pathology, Rajasthan College of Agriculture, Udaipur. Among thefungicides tested, Azoxystrobin 8.3% + Mancozeb 66.7% wg was the most effective fungicide that caused 100%inhibition of mycelial growth of all the six isolates of A. alternata followed by Azoxystrobin 23% sc at 500 and 1000ppm, and neem oil at 0.5% was found most effective in vitro. In field condition most virulent isolate (UDP Aa-1)were used for artificial inoculation with spore suspension having concentration 1 × 103 conidia/ml on the plants of45 DAS. Among the ten treatments, combination of Azoxystrobin 8.3% + Mancozeb 66.7% wg at 0.36% + Neemoil at 0.5% was found most effective in reducing the disease intensity and increase seed yield followed by individualapplications of Azoxystrobin 8.3% + Mancozeb 66.7% wg at 0.36% over untreated control. These results suggest thatbotanical extract with fungicides has a great potential to control the leaf spot disease of soybean in eco-friendly way.