Foliar phosphate fertilization: a simple, inexpensive, and unregulated approach tto control HLB

Foliar phosphate fertilization: a simple, inexpensive, and unregulated approach tto control HLB

Report Date: 05/17/2019
Project: 18-024   Year: 2019
Category: Horticultural & Management
Author: Eric Triplett
Sponsor: Citrus Research and Development Foundation

The experimental design of the Polk County field trial is completed. Christopher Vincent has designed this trial carefully to include sufficient replication. He also planned the trial to reduce the effect of disease severity variablity on the results of the experiment. There will be ten replications for each of the four treatments and three trees per experimental unit. Only the middle tree will be sampled for CLas titer. The canopy denisty of each tree will also be measured.

The trees in the Poly County trial will be sampled next Tuesday prior to the first phosphate applications. This will give us baseline numbers on disease severity in each tree. The first phosphate spray applications will occur later that same week. Trees will be spray with one of four phosphate concentrations, including one treatment with no phosphate.

Another trial is being planned with Southern Gardens in Hendry County. With the two sites, we will have field trials in the two major soil types for citrus in Florida. We are delayed in the establishment of ths site as Southern Gardens continues its search for plots that would be suitable I do not expect this to take very long. Southern Gardens is committed to doing this.

The current plan is for Nian Wang’s lab at the CREC to determine CLas titer in samples from the Polk County trial. The Hendry County samples will be processed in Eric Triplett’s lab in Gainesville.

Meanwhile, the Triplett and Killiny labs have greenhouse experiments underway. In the Triplett lab, the optimal level of phosphate comcentration for foliar fertilization has been determined. Also, a new experiment is underway to compare calcium phosphate fertilizaiton on roots versus foliar phosphate fertilization. The former is expected to mimic field conditions where the plant is forced to reduce the pH to solubilize phosphate. The leaf sprays will mimic the intervention we have planned for the control of HLB.

In the Killiny lab, similar experiments are underway in the greenhouse as described in the paragraph above. In all of these greenhouse experiments, Killiny will measure citrate levels in leaf midribs from all treatments.

We will sample eight leaves per tree, four times each year for CLas titer. Canopy density will be used to measure disease severity. We plan to spray the plants four times a year.

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