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

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

Report Date: 11/10/2021
Project: 18-024   Year: 2021
Category: ACP Vector
Author: Eric Triplett
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them: Objective 1: Determine the level of foliar phosphate fertilization required to reduce phloem citrate levels to less than 0.5 mM, a level that does not support L.crescens growth. A phosphate spray of 6mM reduced citrate levels in the phloem significantly more than other treatments, to a level of ~28mM. Objective 3: Use the phosphate level from Objective 1 in the field trials to demonstrate the reduction in phloem citrate levels and reduction in phloem CLas titers as well as effects on fruit quality and yield.  CLas titers were not significantly reduced by phosphate spray treatments of 0.667, 2.0, 6.0, 18.0mM when compared to a 0.0mM control in 2019, 2020, and 2021.  Effects on fruit quality and yield were measured using Leaf Area Index (LAI), fruit number/m^2, and fruit weight/10 fruit (kg) in two separate field trials (Immokalee and Hamilton field trials). Hamilton results for LAI show an increase in leaf area index from 2019 to 2020 for all treatments, and a slight decrease from 2020 levels in 2021.  Yield results are lower from 2020 to 2021. For the Immokalee trial, LAI results improve and are more uniform in 2021 compared to 2019 and 2020.  Yield results improve for all treatments from 2020 to 2021.  2.  Please state what work is anticipated for next quarter:CLas titers will continue to be monitored in our field trials.  LAI measurements and yield data will be collected seeing that there is an improvemet over the years and in 2021.  Furthermore, compared to 2020, in the year 2021 all tree managment was resumed to pre-COVID 19 pandemic regimes therefore we expect to have definitive data in 2022.  A no-cost extension would allow us to complete the objectives.  In particularly, we want to see if CLas titer in psyllids has declined – which is an objective of the proposal. In addition, we need to measure citrate levels in leaf petioles in our groves.We also need to complete three manuscripts.  3. Please state budget status (underspend or overspend, and why): The project took time to get off the ground.  It took longer than expected to identify the grove we could use in two locations.  The budget remaining is $55,341.70 in direct costs and $6,641.09 in indirect costs.    


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