ABSTRACT
Soybean target spot, caused by the fungus Corynespora cassiicola, can be controlled by using cultivars less susceptible to the fungus, crop rotation and fungicide applications. The most recently registered group of site-specific fungicides are succinate dehydrogenase inhibitors (SDHI). However, excessive use of these site-specific fungicides can contribute to the selection of less sensitive populations. The present study aimed to assess the sensitivity of 54 C. cassiicola isolates to the SDHI fungicides bixafen and fluxapyroxad. The isolates were obtained from soybean (n=53) and cotton (n=1) leaves collected in five soybean-producing regions in Brazil (MT, PR, GO, MS and MA) from 2014 to 2018. The half-maximal effective concentration (EC50) was determined by using the colorimetric microtiter plate assay. The EC50 values ranged from 0.02 μg mL-1 to 37.80 μg mL-1 for bixafen and <0.0125 μg mL-1 to 44.40 μg mL-1 for fluxapyroxad, indicating the presence of C. cassiicola isolates with lower sensitivity to the tested fungicides. Isolates with higher and lower sensitivity were found in the same location, emphasizing the importance of adopting anti-resistance strategies, such as limiting the number of applications of one same chemical group and combining site-specific with multi-site fungicides to prevent the increase in less sensitive populations.
Keywords
chemical control; target spot; carboxamide; resistanc