2019-12_18-034C – Improved postbloom fruit drop management and exploring PFD spread in Florida

Improved postbloom fruit drop management and exploring PFD spread in Florida

Report Date: 02/05/2020
Project: 18-034C   Year: 2020
Category: Other
Author: Megan Dewdney
Sponsor: Citrus Research and Development Foundation, Inc.

January 2020
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.
Planning commenced for the upcoming spring’s field trial. Some infected flowers and persistent calyxes have been seen in groves in the state. We are looking for a site for the timing trial that is a hot spot for PFD in priority but hopefully another site for a fungicide trial. Treatments are being decided upon.
Despite obtaining interesting data in the wind tunnel trials, we failed to obtain enough flowers to study the dispersal of C. acutatum from infected flowers. It would be very interesting to better understand the dispersal of conidia produced during this life stage of the pathogen, since it is the most important for inoculum production and PFD epidemics. We are currently attempting to obtain flowers from greenhouse plants. We intend to test the same treatments as assessed before in the wind tunnels with PFD-symptomatic flowers.
We have yet to finish developing the risk map for PFD in partnership with UF’s agricultural and biological engineering department.
We gathered data on the number of alerts within a season for several locations and seasons. We intend to develop a database to show growers the importance of weather to PFD epidemics. The database will be the base for the development a risk map for PFD in the future. So far, we have noticed that recent seasons were not very conducive to PFD development, especially when compared to 2015/16. We have shared this info with some growers recently. We calculated daily PFD risks using the model adapted from Lima et al. (2011) and currently used in the Citrus Advisory System. Our data corroborates with our hypothesis that the disease was more important to FL growers when conditions were more conducive to PFD according to our model.
The experiments with the flower extracts did not work because of unexpected fungal contamination of the extracts twice. New trials are to be started shortly after filter sterilizing the extracts to remove what are apparent contaminents. All other components were sterile and so we think the extracts were the source of the fungal contaminents.
Dr. Yu Wang’s lab was starting a more comprehensive analysis of the consitituents of the water extracted flowers from the different developmental stages.

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