How Far can the Inoculum for Citrus Black Spot Travel Up?
Posted August 2025
Researchers: Megan Dewdney
Contact: Megan Dewdney, UF/IFAS CREC mmdewdney@ufl.edu
Summary:
Citrus black spot is a quarantine disease that causes fruit symptoms that can lead to significant yield loss in bad years. To date, it is primarily in the southwest Florida citrus production region, although it has been found further north more recently. In Florida, only one type of spore is present to cause disease rather than the two found in most other places. The spores present in Florida are moved by splash short distances (less than 32 inches), mostly downwards from their source. They are recorded to only travel 3 inches upwards. However, when looking for the major source of spores, we discovered that they were primarily in the leaf litter throughout the year. The question that needs to be answered is are those spores in the leaf litter traveling up into the canopy and if so, how. We are developing a spore trapping system to collect spores in an array from the grove floor to the top of the canopy to see how many spores are collected and what the weather conditions were like at the time they were captured. This will help establish how far these spores can travel under the wind-blown rain conditions found in Florida. The information will help us understand how this disease, which is not supposed to spread quickly or far is being moved long distances and help us understand the role of extreme weather events like tropical storms. Currently, the spore trap towers are under construction and should be deployed soon.
Take Home Message:
- It is unusual to have only the splash dispersed form of spores for citrus black spot.
- It is not understood how the spores move from the high inoculum leaf litter to the top of the tree canopy.
- The data from this study will help us understand how the spores move within a grove and spread the disease.
