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POSTERS: Chemical control

Zinc nanoparticles offer systemic efficacy against ‘Candidatus Liberibacter asiaticus’ improving yield
Evan Johnson - University of Florida. Swadeshmukul Santra- University of Central Florida, Mayara Mari Murata- University of Florida, Megan Dewdney- University of Florida

Huanglongbing (HLB), caused by the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus’ (CLas), is the yield limiting factor in many citrus producing regions. Because of the difficulty to reach phloem tissue with chemical treatments, a 2-3 nm zinc oxide-based nanoparticle, Zinkicide, was designed for systemic activity with traditional foliar spray or soil drench application. A canker bioassay demonstrated systemic efficacy. Greenhouse trials have confirmed significant reduction in CLas populations by an average 2.54 log in 20 weeks when applied at a biweekly schedule to maintain an effective dose in the phloem. Multiple field trials on grapefruit and sweet orange were carried out for multiple years on trees of varied age and size. Surprisingly, when the nanoparticle synthesis was reformulated to tolerate impurities in agricultural grade starting materials, nanoparticle size became smaller and field efficacy improved leading to yield increases up to 73%. Young grapefruit trees have responded better than mature sweet orange trees. Dilution effects, preventing effective doses existing systemically, are the likely cause of this apparent tree size dependent efficacy. Hurricane Irma provided a unique opportunity to observe that Zinkicide reduced leaf loosening, leading to much less leaf drop damage from hurricane force winds in young non-bearing trees. Zinkicide nanoparticles show promise as a management tool for young plantings to reach profitability.