Reduction of cladode brown spot in cactus pear in semiarid growing areas and yield increase using fungicides

Cladode brown spot (CBS) is the most common disease in cactus pear in Brazil. It has been associated with fungal species belonging to different genera, including Alternaria, Colletotrichum, Curvularia, Fusarium, Lasiodiplodia, Neofusicoccum, Neopestalotiopsis, and Nigrospora. Due to this complex etiology, the effective control of CBS is difficult. In this study, we analyzed the potential of the fungicides cyproconazole, metiram, difenoconazole, pyraclostrobin, and thiophanate-methyl to control the growth of pathogens in vitro and to control the disease in semiarid growing areas. A total of 15 isolates representing different species associated with CBS were grown in PDA media amended with the fungicides at different concentrations. The concentration of fungicide to inhibit the mycelial growth by 50% (EC50) was obtained, and ranged from 0.1 to >300 μg∙mL−1. Overall, the fungal species were more sensitive to difenoconazole (EC50 average of 0.77 μg∙mL−1) and less sensitive to thiophanate-methyl (EC50 average of up to 40 μg∙mL−1). The effectiveness of the fungicides was also evaluated in vivo, by applying the fungicides in naturally infected plants in cactus pear growing areas. All fungicides were able to reduce CBS, and pyraclostrobin showed the best results, not only in controlling the disease, but mainly in providing the highest yield increase.