The citrus session at the Florida Grower Citrus Show started off with a special award acknowledgement by Ron Cave, director of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center (IRREC). Cave recognized Pasco Avery for his induction into the 2022 class of the IPM Hall of Fame from the Southern IPM Center. A biological scientist at IRREC, Avery is a world leader in the study of entomopathogenic fungi used for biocontrol.
Michelle Heck, research molecular biologist with the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) spoke about her research on symbionts to treat HLB. Symbionts, which can be used in both established groves and new plantings, produce and deliver therapeutic molecules directly into citrus trees to improve their health. Trees are not altered in any way; modification is limited to the symbiont. This strategy is working in the greenhouse, and field trial planning is underway. The technique is a continuous whole plant treatment without repeated spraying.
WORK WITH DRONES
John Chater, UF/IFAS assistant professor, summarized his work using drones to measure citrus tree health. Drones were flown over 1,337 acres of citrus, including 91 sites composed of scion and rootstock trials, commercial groves and germplasm repositories. The goals of the study included providing an inventory of what is planted and a list of top performers. While data is still being analyzed, among the shining stars for sweet oranges are N13-32 on UFR-4 rootstock and the OLL varieties.
NEW NUTRIENT RECOMMENDATIONS
Kelly Morgan, UF/IFAS professor, shared recent updates to citrus nutrient guidelines. The recommendations for foliar manganese and zinc have increased from 3–5 pounds per acre per year to 15 pounds per acre per year. For soil applications, the amount has increased from 7–10 pounds to 25 pounds. Currently, UF/IFAS has no set recommendations for calcium and magnesium other than pH maintenance.
There were several take-home messages from Tripti Vashisth’s presentation on plant growth regulators (PGRs) to improve the health of HLB-affected trees. The UF/IFAS associate professor stressed that more leaves mean more potential for fruit production, and timely PGR application is critical. Gibberellic acid can improve yield efficiency in Hamlin and Valencia, while 2,4-D is showing promise in reducing fruit drop. Cytokinin, a growth hormone, may also be helpful in holding fruit on trees.
LEBBECK MEALYBUG IDENTIFICATION
In 2020, lebbeck mealybugs became a problem in Florida citrus. The pest can be difficult to distinguish from other mealybugs, but Muhammed Ahmed, USDA ARS research entomologist, discussed an easy, five-minute method for identifying the pest. He tested 57 species of mealybugs and only lebbeck mealybug turns green when dipped in potassium. This applies to all life stages of the pest.
SCIONS AND ROOTSTOCKS
Several citrus breeders gave updates on variety and rootstock research.
Kim Bowman, USDA ARS research geneticist, detailed two new SuperSour rootstocks with exceptional performance. US-1688 and US-1709 (tentatively named US SuperSour #4 and US SuperSour #5, respectively) are expected to be commercially released later this year. Both have demonstrated superior multi-year performance with Valencia and Hamlin scions on Flatwoods and Ridge sites. These rootstocks produced better yield, canopy health and total soluble solids than Swingle, Sour Orange and other rootstocks.
Among the selections UF/IFAS professor Jude Grosser called attention to in his presentation were UF-1859 sweet orange-like hybrid and C2-5-3 grapefruit-like hybrid. UF-1859 has good HLB tolerance and high Brix. C2-5-3 is a new and distinct early-season fruit for the fresh market. It is more tolerant of HLB than standard grapefruit and is also tolerant to citrus canker. Both UF-1859 and C2-5-3 have been released.
Other USDA ARS speakers were Yong Ping Duan, who discussed evaluation of citrus bud sports for HLB resistance/tolerance; Anne Plotto, who spoke on potential HLB-tolerant citrus hybrids for orange juice; and Matt Mattia, who presented information on new citrus scion selections. Mark Ritenour, UF/IFAS professor, concluded the seminars with an update on the Millennium Block grapefruit scion/rootstock trials at IRREC.
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