In the quest for better fruit retention in HLB-infected citrus, there has been a good deal of attention placed on the use of plant growth regulators to fight fruit drop. Gibberellic acid (GA) has been the focus of new research in recent years to establish refined timing of applications to optimize results in Florida citrus.
Much of that research has been conducted by Tripti Vashisth, an associate professor of horticultural science with the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS). Her research has uncovered the benefits of multiple applications of GA.
That work prompted Valent U.S.A., manufacturer of ProGibb LV Plus, to seek a supplemental label from the U.S. Environmental Protection Agency (EPA) that would allow more applications of the GA product.
Because of the interest and questions she was getting from growers, Ajia Paolillo, UF/IFAS multi-county citrus Extension agent, hosted a meeting in Wauchula, Florida, with Valent to share information with growers.
“What the supplemental label allows is up to four applications of the product from August to December no closer than four weeks apart,” said Craig Campbell, Valent senior field market development specialist. “This is important because our previous label didn’t allow for four applications. I am sure everyone in the room knows about the UF/IFAS research that shows that four or five applications dramatically improves growth of citrus trees and reduces fruit drop. It also helps improve fruit set with later applications by reducing the amount of bloom.”
Campbell added he fully supports the research and recommendations coming out UF/IFAS in terms of applications of GA. He reminded growers that while the supplemental label only covers four applications, they can still follow UF/IFAS recommendations of up to five applications.
“Our full label and the use patterns on our supplemental label are not mutually exclusive. So, if you want to make five applications on Valencia, we have you covered,” he said. “You just can’t make applications closer than 30 days apart.”
Growers had many questions during the meeting about timings of applications, potential for root drenching of gibberellic acid, and the nexus between flush induced by the product and the need for supplemental fertilizer applications. Campbell acknowledged all were good questions, but some needed further research and/or label updates.
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