December 2017 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. In 2018 we have recorded the number of spores from field collected dead twigs from 2016 to August 2017. We have found relatively low numbers of spores from the twigs and we are unsure if this because limited numbers of spores are being produced or that we are not effectively capturing them. We have also started to evaluate the level of P. citricarpa DNA from the twig bark. We consistently find low level presence of P. citricarpa DNA but it increases over time. More data will tell us if this is a seasonal effect. The first four temperatures of the temperature and relative humidity (RH) experiment were conducted with twigs. Low numbers of pycnidia to none were formed at %RH less than 100%. This does not correspond with previous data but we have determined that the drying conditions post inoculation is likely the culprit. The fungus is not dead as pycnidia can form when the lower %RH treatments are placed at 100% RH for an additional month. We are working to resolve this problem with a less rigorous drying regimen. The temperature and relative humidity experiment on leaf tissue was more successful. Both temperature and relative humidity had a significant effect on the number of pycnidia formed on the leaf disks. As expected, pycnidia formation was slower at cooler temperatures (16 and 20C). Relative humidities less than 85% did not form pycnidia. Unfortunately, when the DNA data was examined, it was revealed the the growth had been the endophyte P. capitalensis, which may not have the same sporulation pattens as P. citricarpa. We will be repeating this experiment with autoclaved leaves. This is not as satisfying because we cannot look a the the infection process as well but at least we will be better able to study what P. citricarpa is doing rather than the endophyte. Decontamination work continued this year adding the factor of debris to the study. Debris significantly reduced the efficacy of the decontamination materials but they are still effective at the recommended rates of quaternary ammonium and bleach. Bleach was more affected by the presence of debris than quaternary ammonium. Interestingly, higher volumes of disinfectant were more effective than lower volumes.