September 2015 The objectives of this proposal are 1) To determine the temperature and relative humidity optima for Guignardia citricarpa pycnidiospore infection and production on citrus twigs, leaf litter, and fruit; 2) To determine the relative potential of Guignardia citricarpa to form pycnidiospores on citrus twigs, leaf litter, and fruit; 3) To determine whether Guignardia citricarpa can survive and reproduce on citrus debris on grove equipment. Experiments to confirm initial relative humidity findings continue. A new set of twigs was inoculated and incubation started but it is unlikely to see structures for at least 4-6 weeks. An employee was hired to assist with this project. A site has tentatively been found to conduct field experiments of inoculum potential and some preliminary work is underway. Assays to determine the survival of P. citricarpa pycnidiospores following exposure to temperatures ranging from 5 to 50�C, for periods of 1 to 48h were completed. We have determined that spore germination increases with increasing temperature to a maximum at 25�C and declines at 30�C and above. Over time, incubation periods of up to 3h do not have an impact on the survival of the pycnidiospores at temperatures of 15-30�C. Across all time and temperature treatments, exposure of spores to drying and subsequent low relative humidity was significant, essentially eliminating spore viability. These results are providing valuable information for modeling the potential for spore survival in and on equipment associated with grove operations. Additional experiments to assess the environmental conditions associated with optimal pycnidiospore production have been established and are ongoing. Preliminary results suggest no, or only a modest influence of light on spore production in culture and experiments to test the influence of temperature and relative humidity are ongoing.