A common problem that many citrus growers face annually is post-bloom fruit drop. This disease is caused by a fungus known as Colletotrichum Acutatum. The fungus survives between bloom periods as resistant structures on the buttons, leaves, and twigs.
When flowers first open on a tree, this fungus begins to germinate and form spores. These spores are moved via rain to the owers, where they are able to germinate and infect more owers while producing more spores. These spores are then transported to the surrounding owers via rainfall. is disease is highly dependent on rainfall. Because of this, weather events such as El Niño and groves or cultivars that have multiple or extended blooms tend to make post-bloom fruit drop more prevalent.
“The spores of the fungus are produced directly on the surface of infected petals and then splash- dispersed by rain to adjacent healthy owers. Once the owers are infected, the young fruitlets will drop from the tree, thereby reducing the crop,” says Dr. Stephen Futch, a UF/IFAS extension agent that specializes in citrus production and weed control.
Groves with persistent calyxes from previous years should be closely examined once the bloom begins. If infected owers are present on scattered early bloom, fungicide application recommendations should be followed once suffcient bloom is present for the fungicide application to be economical. Groves with a history of post-bloom fruit drop should be checked twice weekly during the bloom period.
As far as what’s being done to control this disease, Dr. Futch explains “researchers are conducting trials to continue to optimize chemical rates as well as timing to obtain the best control of the fungus.”
As we inch closer to bloom, be mindful of post-bloom fruit drop and the conditions that cause the fungus to thrive. Be proactive and check your trees and cultivars regularly, especially during rainy weather or if you’ve had a history of the fungus in previous years.