Pathogens Identified as Cause of Citrus Fruit Drop

Cindy Zimmerman

Research conducted in the European Union by KeyPlex at the University of Torino in Italy have determined causes of fruit drop on citrus, and the results will help to guide the citrus industry into the future.

While fruit drop was thought to be caused by physiological conditions and other pathogens such as huang long bing (HLB), the research has clearly identified Colletotrichum gloeosporioides and further fungal pathogens as playing a major role.

Since fruit drop causes significant crop loss in oranges, lemons, grapefruit, limes, and other types of citrus, it is a major concern for the industry. Dr. Vladimiro Guarnaccia, associate professor of Plant pathology at the University of Torino and a lead researcher on this project, will present the methods and results of his team’s two years of work at the third and final KeyPlex Citrus Symposium on July 25, 2024, at Seven Sebring Raceway Hotel in Sebring, Florida. Most importantly, he will present solutions to aid citrus growers, such as agronomic practices and control methods based on his observations and preliminary tested conclusions.

“We started hypothesizing that Glomerella cingulata — the sexual phase of C. gloeosporioides — was the main cause of early fruit drop in citrus, not HLB, as has been long presumed,” says Gerald O’Connor, CEO of KeyPlex. “We scoured the world looking for information on this and came across Dr. Guarnaccia, who was already working on it at the University of Torino. We are excited to present the results of this groundbreaking research — the result of many years of work — that will help the citrus industry.”

Contact O’Connor at for a personal invitation.

Citrus, Research