By Fernando Alferez and Saoussen Ben Abdallah
The risk of citrus plantings to become infected with HLB is especially high for young trees, which flush frequently and attract more psyllids than mature trees. Individual protective covers (IPCs) are now being increasingly adopted to protect newly planted citrus trees from psyllid colonization.
However, even though IPCs effectively protect young trees from HLB, it is only for the first two to three years after planting. Eventually, covers must be removed, which exposes trees to the disease vector. Under these circumstances, it is advantageous to prolong tree health by means affordable to growers, so trees have several years of high-quality fruit production and increased yield.
Brassinosteroids (BRs) are a natural group of hormones approved for use commercially in citrus in Florida. BRs have shown promise in reducing pests and diseases. University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) researchers have shown that with BR treatment, HLB progression is delayed in newly planted trees. Furthermore, psyllid colonization and egg deposition are reduced in new flushes, and rust mite incidence is reduced as well.
With funding from the U.S. Department of Agriculture National Institute of Food and Agriculture, UF/IFAS researchers are now investigating the combined use of IPCs and BRs for enhanced protection of citrus trees against HLB as well as other diseases that limit citrus production in Florida. Testing is taking place using different varieties, including Tango and Early Pride mandarins, as well as Hamlin and Valencia oranges. This research is now in its third year.
After IPC removal in the third year, following monthly foliar spray applications of BRs at a rate of 6.2 fluid ounces of product in 100 gallons of water, trees remain HLB-negative for about six months. In addition, fruit yield is increased by 30% on average in BR-treated trees. Tree growth is significantly increased with monthly applications of BRs. HLB infection eventually progresses in these trees, but healthier trees may cope better with antibiotic injections.
Acknowledgement: This research is funded by USDA-NIFA project 2022-70029-38481.
Fernando Alferez is an associate professor, and Saoussen Ben Abdallah is a postdoctoral associate, both at the UF/IFAS Southwest Florida Research and Education Center in Immokalee.
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