APS Homepage

POSTERS: Chemical control

Fungicide applications prevent Colletotrichum acutatum secondary conidiation from appressoria and conidiogenous hyphae on citrus leaves
André Bueno Gama - University of Florida. Megan Dewdney- University of Florida, Natalia Peres- University of Florida - Gulf Coast Research and Education Center

Colletotrichum acutatum causes postbloom fruit drop of citrus (PFD), an important disease in the tropics that may result in significant yield losses during rainy seasons. PFD epidemics are initiated by conidia produced from quiescent appressoria when bloom occurs. The appressoria germinate on leaves and produce a small number of conidia when stimulated by substances that are washed-off from flowers or by sucrose. Conidia that successfully infect flowers produce acervuli on which copious conidia are formed. Our objective was to investigate new management approaches to control PFD that focus on reducing inoculum density or preventing the production of secondary conidia from hyphae or appressoria. We tested the effect of a multi-site fungicide (ferbam) applied to leaves with or without a sucrose stimulant. Two experiments assessed the effect of ferbam (1.8 g.L-1) on conidiogenous hyphae and appressoria. Two other experiments assessed the effect of ferbam on melanized appressoria. The number of conidia, appressoria, and colony forming units (CFU) was counted. Ferbam hindered secondary conidiation in all experiments. The number of conidia and CFU in treatments that received the fungicide application was, respectively, 49-98% and 82-100% lower than in those on which sucrose was applied. Ferbam applications during periods of secondary conidiation stimulation suppress inoculum production and might be applied as a new strategy to manage PFD in citrus orchards.