Pathogens Identified as Cause of Citrus Fruit Drop

Learn About Results and Solutions July 25, 2024 at the KeyPlex Citrus Symposium at SEVEN Sebring Raceway Hotel

WINTER PARK, FLORIDA, JUNE 20, 2024 – Eleven years of research conducted in EU have determined causes of fruit drop on citrus, and the results will help to guide the citrus industry into the future. Fruit drop, in particular, was thought to be caused by physiological conditions and other pathogens, such as huang long bing (HLB). However, research sponsored by the European Union and KeyPlex at the University of Torino in Italy 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.”

Email Gerald O’Connor at for a personal invitation.

Read the full report:
Lasiodiplodia iraniensis and Diaporthe spp. Are Associated with Twig Dieback and Fruit Stem-End Rot of Sweet Orange, Citrus sinensis, in Florida

About Vladimiro Guarnaccia: Dr. Guarnaccia is associate professor of Plant Pathology in the Department of Agricultural, Forest and Food Sciences, University of Torino, and researcher at the Interdepartmental Centre for the Innovation in the Agro-Environmental Sector, AGROINNOVA. In 2013, he obtained his Ph.D. in Plant Health Technologies and Protection of Agro-Ecosystems at University of Catania, Italy, working on fungal pathogens of citrus, avocado, and ornamental plants. He worked as a postdoc researcher at Westerdijk Institute in Utrecht, the Netherlands, and at University of Stellenbosch, South Africa, focusing on several citrus diseases caused by Colletotrichum, Diaporthe, Fusarium, Neofusicoccum, Lasiodiplodia, and Phyllosticta species. His current research includes fruit crops (blueberry, apple, citrus), grapevine, and hazelnut. He is currently working on disease etiology, epidemiology and control.

About Keyplex: Since its inception in 1980, KeyPlex has been a leader in plant nutrition, biocontrols, and oil-based botanical research. The company’s offerings are part art and part science — helping growers to unlock the complexity of plant health and vector control. Operating in more than 16 countries, KeyPlex serves the specialty fruits, vegetables, citrus, tree nuts, row crops, greenhouse, and turfgrass markets with highly effective plant nutrition and biopesticide products. KeyPlex provides a wide range of solutions to meet its customers’ unique needs.

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