July 2019 The objectives for this proposal are 1) Conduct field trials of new products and fungicide programs for PFD management as well as validation trials for the Citrus Advisory System (CAS); 2) Investigate the reasons for the movement of Postbloom fruit drop (PFD) to new areas and recent major outbreaks; 3) Evaluate methods for initial inoculum reduction on leaves so that early fungicide applications could be more effective and identify the constituents of the flower extracts using omics techniques. Objective 1 was mostly covered by project 16-010C and activities are also reported there. In 2019, a field trial was set up and treatments were applied in a Valencia grove in Ft. Meade. There were few predicted infection events this year and only one application was made based on the PFD-FAD or CAS model predictions. Button counts were collected. There were also two CAS model validation trials and button data were also collected for both of these. Fruit data should be collected by the end of July for all the trials. The experiments with the wind tunnel located at the ARS facilities in Ft. Pierce have commenced although access is still limited as progress is made for the USDA screening process. We hope to finish the screening process in the very near future for greater access. Preliminary trials with Colletotrichum acutatum in the wind tunnel indicates that the spores are able to move considerable distances in the wind alone. The modelling to indicate possible distances and gradient are very preliminary but indicate that some modifications to the experimental set up may be needed including increasing the number of repetitions since the variability was high. Work on modelling of leaf wetness to better predict PFD outbreaks in Florida is on-going. Five FAWN weather stations were selected for this work and are equiped with leaf wetness sensors. The recorded data was compared to the output of four leaf wetness estimation models, singly and in combination. The most accurate models were considered for modifying the citrus advisory system (CAS). Analyses to look at the number of recommended sprays and model accuracy are underway. Experiments to assess the effect of available fungicides on the secondary conidiation of C. acutatum on citrus leaves. In the intial experiment, pyraclostrobin was used and no difference was seen in the secondary conidiation regardless if sugar or water were used for stimulation of conidia. In subsequent experiments, ferbam was used instead. To stimulate sporulation, leaves were exposed to sterile water or 2.5% sucrose solutions with or without ferbam. Once the treatments were complete, the leaves were coated with nail polish and the conidia and appressoria stripped from the leaf surface and counted. Ferbam affected the viability of the spores but not the number produced. It also signficantly reduced the number of appressoria. These techniques are being used to assess the effect of the water, methanol, and ethyl acetate extracts of the flowers. Preliminary trials with the extracts are underway to make sure that the experimental procedures developed for the fungicides will be adequate or if modifications will be necessary. Flowers were collected and extracted using water, methanol and ethyl acetate. The yields of all the extracts have been calculated for future reference. All the extracts have been dried for testing their antifungal effects. Once we receive the antifungal effects of the extracts, we will start the composition analyses. Preliminary metabolomics analyses are planned once some data from the fungal tests are available.