Field efficacy and post-application persistence of a new strain of Cordyceps javanica

A naturally occurring strain of Cordyceps javanica (Wf GA17) caused widespread epizootics among whitefly, Bemisia tabaci, populations in cotton fields located in southern Georgia in 2017. Previously, laboratory tests showed that this strain of C. javanica demonstrated higher virulence against B. tabaci and better temperature tolerance than the commercial strain of C. fumosorosea (Apopka97). The overall goal of this study was to evaluate field efficacy against B. tabaci and post-application persistence of C. javanica Wf GA17 compared to C. fumosorosea Apopka97. Specific objectives were to 1) assess the survival of conidia versus blastospores of both fungi at different times after spray, and 2) test if horticultural oils could enhance field persistence and efficacy of blastospores against B. tabaci. In field persistence assays, percentage deposition and propagule survival were determined separately on upper and lower leaf surfaces by assessing the number of colony forming units recovered after application. In field efficacy tests, immature B. tabaci mortality and mycosis levels were evaluated by sampling infested cotton leaves at 0, 7, 14, 21 and 28 days after application. We hypothesized that C. javanica Wf GA17 would have superior field persistence compared with C. fumosorosea Apopka97 and achieve equivalent or higher field efficacy for managing whiteflies under favorable conditions.