Oak Leaf Extracts Display Curative Effects Against HLB

Tacy Callies HLB Management

HLB-infected citrus leaves

As demand increases for a cure to huanglongbing (HLB), experts are studying the most effective ways to control the damaging citrus disease. A research project funded by the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is focusing on the effects of oak leaf extracts on CLas-infected citrus trees. CLas (Candidatus Liberibacter asiaticus) is the bacteria the causes HLB.

Robert Shatters, a U.S. Department of Agriculture (USDA) research molecular biologist, presented findings from the oak leaf extract research in a virtual education session on July 22. The Citrus Research and Development Foundation session was hosted by Florida Citrus Mutual.

For years, Florida growers have noticed that citrus trees standing under oak tree canopies or alongside oak trees appeared healthy with no HLB symptoms. However, citrus trees located a row or two away displayed signs of HLB.

To test the effects of oak leaf extracts on citrus trees, a team of UF/IFAS and USDA researchers grew citrus trees in the screened U.S. Horticultural Research Laboratory greenhouse in Fort Pierce, Florida, using routine horticultural practices.

Plants were graft-inoculated with 3- to 4-centimeter CLas-positive Valencia bud sticks. Three symptomatic CLas-infected citrus plants were supplied with the oak extract, receiving bi-weekly applications for two months. For each treatment, 50 milliliters of the oak extract were foliar applied, and 200 milliliters of the extract were drench applied. As a control, distilled water was applied to three CLas-infected plants.

Based on the results of the study, researchers found that citrus leaves treated with oak leaf extracts showed a decrease in the presence of bacteria. Other results from the study suggest that oak leaf extract treatments significantly increased root nutrient uptake and increased chlorophyll content and plant nutrition.

Oak leaf extracts represent a potential organic tool to manage HLB. Although there is more research to be done, this study suggests that oak leaf extracts will provide a new treatment program for trees with HLB.

Ashley Robinson, AgNet Media communications intern, wrote this article.