Fruit drop has plagued Florida citrus groves in recent years. The problem has been a major factor in tumbling yields. The February 2022 U.S. Department of Agriculture’s citrus crop forecast put Florida’s orange estimate at 43.5 million boxes. If realized, it would represent an 18% decline in the crop from last season.
Growers are turning over every stone to seek solutions to the problem, whether it be postbloom fruit drop (PFD) or preharvest drop. While it is known HLB is a key factor driving the problem, there could be many other factors causing fruit drop. HLB only enhances those other factors.
More than 80 growers gathered at Streamsong Golf Resort in Bowling Green, Florida, in early February to attend a symposium hosted by KeyPlex to address the challenge. The focus of the event was the role fungal pathogens play in fruit drop. There is a clear indication that the genus Colletotrichum fungus is playing a vital role. Colletotrichum acutatum has been identified as the main culprit in PFD. Colletotrichum interacting with the fruit and calyx may be contributing to preharvest drop as well. There are nearly 200 species of the fungus, but Colletotrichum gloeosporioides is considered among the most important. It is the pathogen that causes anthracnose.
KeyPlex invited Vladimiro Guarnaccia, a plant pathologist with the University of Torino in Italy, to speak on his twelve years of research on the impacts of Colletotrichum on various crops, including citrus. Guarnaccia has conducted extensive research on the fungal pathogen.
Guarnaccia noted the fungus causes various maladies in crops including both forms of fruit drop, fruit lesions, twig dieback and more. The climate in various regions around the world influences how the symptoms of fungal infection manifest.
He added that C. gloeosporioides is omnipresent in citrus groves. Fruit and leaves that drop to the ground are an excellent source of inoculum for the pathogen. Years of preharvest fruit drop in groves have supercharged populations of the fungus.
Mauricio Flores, a research consultant with KeyPlex, updated symposium attendees on the company’s ongoing research on the pathogen’s influence on drop. The company has pulled leaf and fruit samples in groves that shows large populations of the fungus Glomerella cingulata, which is the sexual stage of the C. gloeosporioides fungi. More than 1,000 samples have been pulled and analyzed since last summer.
With these fungi omnipresent in groves, Flores suggested that growers make fungicide applications part of their production programs to help stem potential fruit drop. While he said timing and rates are still being fine-tuned, the current recommendation is a rotation of fungicides — two in the spring when the calyx is forming and two in the fall before ethylene production takes place. Flores recommended KeyPlex KP-120 be applied with all these applications, because the peptide-based formulation has been shown to contain the spread of Colletotrichum. He said company trials show the synergy between the peptide and fungicide has reduced fruit drop and twig dieback.
“All indications from our research are pointing to controlling Glomerella cingulata will reduce fruit drop,” KeyPlex CEO Gerald O’Connor noted.
Flores added growers should consider management measures aimed at fruit and leaf debris on the ground. He suggested applications of biological digester materials that include beneficial microbes and humic acid to help reduce spores of Colletotrichum being produced as debris decays. He added pest control should be considered part of the equation as insects are likely spreading the fungal pathogens as they move about in groves.
KeyPlex has contracted with Guarnaccia and the University of Torino to further study the connection between Colletotrichum and citrus fruit drop in Florida.
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