In vitro sensitivity of Corynespora cassiicola isolated from soybean to different chemical fungicides in northwestern Argentina.

REZNIKOV, S.; BLECKWEDEL, J.; CLAPS, M.P.; GONZALEZ, V.; SAUTUA, F.J.; CARMONA, M.A.; PLOPER, L.D.

Viena

Congreso; World Soybean Research Conference XI (WSRC XI); 2023

Donau Soja Association (Vienna, Austria) - Institute of Field and Vegetable Crops (Novi Sad, Serbia)

Book of Abstracts “Soybean Research for Sustainable Development. p. 438. Target spot of soybean, caused by Corynespora cassiicola, has become an important disease in northwestern Argentina (NWA). The Fungicide Resistance Action Committee (FRAC) classifies C. cassiicola as a high-risk pathogen for the development of fungicide resistance. The objective of this study was to determine the fungicide sensitivity of six C. cassiicola isolates to different commercial fungicides. These isolates were collected during the 2014/2015 growing season from soybean fields located in the provinces of Tucumán and Salta, in NWA. The 50% effective concentration (EC50) values were estimated by the relative mycelium growth reduction on PDA medium added with fungicides doses of 0, 0.1, 1, 10, 100 and 1000 ppm of active ingredient. The fungicides used contained: azoxystrobin 25%, trifloxystrobin 50%, pyraclostrobin 25%, difenoconazole 25%, pydiflumetofen 20%, thiophanate-methyl 50%, mixtures containing epoxiconazole 5.0% + pyraclostrobin 13.3%, trifloxystrobin 15.0% + prothioconazole 17.5% + bixafen 12.5%, difenoconazole 12.5% + pydiflumetofen 7.5%, and fluxapyroxad 5.0% + pyraclostrobin 8.1% + epoxiconazole 5.0%. At 7 days, CE50 was estimated for each isolate and chemical product using the methodology by Kataria and Grover (1978). Azoxystrobin and trifloxystrobin were inefficient to control all isolates (EC50 >1,891.3 ppm and >3,103.2 ppm, respectively). Pyraclostrobin was inefficient for four isolates (EC50 >148.8 ppm) and slightly efficient for two isolates (EC50 19.6 to 49.8 ppm). Difenoconazole was moderately efficient for 5 isolates (EC50 1.6 to 6.2 ppm) and slightly efficient for one isolate (EC50 44.2), pydiflumetofen was moderately efficient (EC50 1.7 to 5.8 ppm), the mixture of epoxiconazole + pyraclostrobin was also moderately efficient (EC50 1.8 to 8.1 ppm) and so was trifloxystrobin + prothioconazole + bixafen (EC50 1.1 to 4.1 ppm). Thiophanate-methyl was inefficient for one isolate (EC50 10,471.3 ppm), moderately efficient for another (EC50 3.6 ppm), and highly efficient for four isolates (EC50