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Oak trees may hold antibacterial to help infected citrus trees

Wise old oak trees may hold an extract that citrus growers can use to protect their fruit trees from the deadliest citrus crop disease the world has known.

The plant disease is called huanglongbing, or HLB, also known by its English name, citrus greening. The disease shows its presence when leaves turn lighter shades of green.

According to University of Florida Institute of Food and Agricultural Science’s (UF/IFAS) officials, HLB is responsible for a 90 percent reduction in the production of Florida’s most valuable crop.

“Research scientists work with a sense of urgency to contain the pathogen and to manage HLB’s impact on our important crop,” said Lorenzo Rossi, assistant professor of plant root biology at the UF/IFAS Indian River Research and Education Center (IRREC), located in Fort Pierce, at the center of the Indian River District. The district is known for its peerless grapefruit quality, where it borders the state’s central east coast, from its northernmost point in Micco, Florida, to its southernmost point in northern Palm Beach County.

For several years, growers across the state have noted that citrus trees that stood under oak tree canopies, or alongside oak trees, are healthy. However, grapefruit trees in a row or two away from the oak trees showed signs of HLB.

Rossi, along with his UF/IFAS and U.S. Department of Agriculture colleagues, works to develop management tactics for production of fruit on trees affected by HLB. Marco Pitino and Robert Shatters with the U.S. Department of Agriculture U.S. Horticultural Agricultural Service in Fort Pierce, along with Rossi, were responsible for design of the experiment and preparation of the manuscript. Liliana Cano, a plant pathologists with UF/IFAS, and Kasie Sturgeon, Christina Dorado and John Manthey were responsible for planning, conducting the experiment, and analysis of data and preparation of the manuscript.

Rossi’s co-workers who study citrus horticulture and hydrology developed water and nutrition management practices. Irrigation and plant nutrition remedies help HLB-affected trees tolerate the disease and extend their production years. Projects funded by the Citrus Research Development Foundation and the USDA are underway.

Rossi and his collaborative research scientists have also been conducting research experiments to test the growers’ field observations, which they found to be a positive option to help the growers manage operations with infected fruit trees. The scientists’ work appears in this month’s issue of Plant Physiology and Biochemistry, an internationally prominent science journal. “Quercus leaf extracts display curative effects against Candidatus Liberibacter asiaticus that restore leaf physiological parameters in HLB-affected citrus trees,” is the publication title. Quercus is Latin for oak; Candidatus Liberibacter asiaticus is the scientific name for the bacterium that causes HLB.

“We found that the application of oak leaf extracts in a greenhouse provides substantial inhibitory effects against the bacterium that causes HLB,” said Rossi.

The researchers’ findings were that citrus leaves treated with oak extracts showed a decrease in the presence of bacteria. Other research results were increased chlorophyll content and plant nutrition. The HLB-affected citrus plants treated with oak leaf extract were better able to uptake nutrients than were the citrus plants treated with only water.

“This study suggests that oak leaf extract will provide a new management treatment program to protect trees that have HLB,” said Rossi. “We will continue to develop a protocol for growers to produce our high-value citrus crops and to reduce the symptoms of HLB on the trees.

18 Comments on “Oak trees may hold antibacterial to help infected citrus trees

  1. Could new groves be set up with interplanting of oak and citrus trees? It seems like the citrus trees would have to be resprayed regularly, an expensive process.

    • If the extract of the Oak Tree leaves is effective against HLB, It would appear by developing a harvesting method for the leaves could be achieved and have the extract made into a finished spray in quanties at a processing plant like.Bayer chemicalThey being a good place to start. The challenge to Bayer would be to turn this into a systemic treatment which lasts longer than spraying. Bayer have technology in place which they use on the ash boer as an example.If effective systemically on HLB ,is the need to check the toxicology of the extract regarding potential human probably required. The toxicology study would be required for sprays as well.
      Currently existing for other application using systemics on tree can be effective for a year with one application to the base of the tree.The average cost to do an application tree using an application of 1 ounce per 1 inch of circumference of the trunk of the tree should be affordable.

      • What about integrating the fallen leaves into the soil? &/or using it as mulch?

  2. Please import 3D map of citrus + oak inter cropping method

  3. Check out a poductive feral citrus population videotaped in an oak understory and you can see the benefit. Search youtube for the following, “Wild Citrus in a Florida Forest? Why It’s a Big Deal.”

  4. So is it possibly people are not seeing the forest for the trees on this one. Is it possible that the soil is healthier around oak trees than in a monoculture environment and maybe there is more beneficial bacteria and mychorizae associated with them than a field type environment. ?

  5. I would be curious about the rest of the layers of plants around the citrus and the varietals of oak.

  6. I have several feral citrus trees growing under oak trees in Palm City. Some may be sour oranges, but based on where my dog used to bury grapefruit I believe some are the Duncan variety. I offer these trees for a UF trial study if that would be useful.

  7. If I was to make oak leaf tea to spray my citrus, does it matter if the oak leaves are green or dried brown?

      • Mimic nature. I’m trying it myself, I have nothing to go on but instinct. I’m soaking a 5 gallon bucket full of green leaves for two days, then straining and diluting in my 50 gallon sprayer. Haven’t seen much change but it’s only been 3 weeks, once a week.

  8. The naturally occurring benefits were on citrus trees growing near the canopy of oak trees. This would say to me that it must be the leaves falling from the oaks to the ground that is giving the citrus trees the oak leaf extract.Therefore, it’s brown leaves off the ground that you can use to make your oak leaf tea. I’ve just been brewing a 5gal. bucket of brown leaves, and watering my trees with the tea once a week. I’ve had normal looking fruit from my kumquat tree this spring already, so it might be working!

  9. My guess would be the tannins in the oak leaves have antibacterial components. Therefore mulching with oak leaves can only benefit and also feed the trees. A tea would be faster even if applied to the soil. I also think Justin has a good point with the soil culture.

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