2019 ASHS Annual Conference

Nutritional programs being used in Florida in efforts to maintain productivity from HLB-infected trees were initially focused on foliar nutrient applications. However, we subsequently learned that secondary and micronutrient deficiencies in HLB-compromised trees were twice as great in the roots than in the leaves. Foliar micronutrient applications only temporarily alleviate deficiencies in the leaves, and do not correct deficiencies in the roots. These deficiencies must be corrected in the roots for trees to regain adequate vascular function as necessary to regrow and preserve functional feeder roots. There are several methods available to accomplish this, but we have found soil applications of controlled release fertilizers (CRF) containing enhance micronutrient packages to be quite effective. Fertigation and additional standard dry soluble fertilizer applications have also been successful in various grower programs. Our greenhouse and field data indicates that HLB-impacted trees require a constant supply of the impacted nutrients. Trees under good programs are showing good recovery and productivity, including higher yields of improved quality fruit, and little or no symptomatic fruit. We have also investigated the effects of overdoses of selected micronutrients, and we now have data from multiple experiments showing a therapeutic effect from high manganese. Trees with high leaf manganese content (delivered via the roots) from multiple experiments are showing reduced bacterial (CLas) populations, with qPCR CT values indicating no active infection in many cases. Trees with leaf manganese levels exceeding 60 ppm generally show a strong recovery, and trees exceeding 100 ppm show the therapeutic effect. Data will be presented from two such experiments in commercial groves with no psyllid control, suggesting that focus on root health is much more important than psyllid control, and that growers can go back to more affordable and sustainable IPM programs enhanced for psyllid control.