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: 09/09/2020
Project: 18-024   Year: 2020
Category: Horticultural & Management
Author: Eric Triplett
Sponsor: Citrus Research and Development Foundation

At the start of this quarter, we halfway through the funding period of the project. Our field results in Polk County are showing some early signs of the efficacy of foliar phosphate fertilization. We have been spraying citrus with four levels of potassium phoshate every two months since April 2019 at Polk County and since August 2019 in Collier County.

The copy number of the CLas terC gene per ng of DNA had declined significantly with the 2 mM phosphate spray after one-year of treatment (p-value = 0.029). We were surprised to see such a result so early in this study. We expect to see yield improvements next spring.

Data is still being analysed from the Imokalee trial. We hope to have those done by the end of this month. This will give a sense of the progress from one year of spraying in Collier County.

Meanwhile, a greenhouse trial continues to show great promise for prevention of HLB by spraying phosphate on uninfected trees. Nabil Killiny’s group graft infected young saplings with in February 2019. These plants were given a potassium phosphate foliar spray, a calcium phosphate soil drench (to mimic FL soils), or no added phosphate other than what is in the typical fertilizer mix. Eighteen months later, the K-phosphate treated plants have no symptoms. The other treatments show severe symptoms. We jut sampled this plants and hope to have CLas titer done very soon.

We plan to submit a paper soon based on the results from the grafting experiment.

I am pleased to report that this project is working as planned so far. Earlier we showed that foliar potassium phosphate does reduce citrate levels and the levels of other organic acids in phloem. As organic acids, particularly citrate, are the preferred carbon source for Liberibacter crescens, we expect this treatment to starve the pathogen.

We are seeing that foliar K-phosphate prevents HLB symptoms in young saplings. We are seeing the beginnings of improvements in older trees with high titers. CLas is decling in the Polk County plots. To early to see symptom relief in the older field trees. We expect to see a yield improvement in the spring.

Our team (Triplett, Vincent, Killiny, and Wang) are working very well together and meet to discuss the project regularly.

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