Roots, Shoots, Fruits & Flowers: Oak Treehoppers, Southern Bacterial Wilt, and the “Ooze” Test

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Oak treehoppers.
Photo: John Stebbins.

Oak treehoppers

John S. sent in several images of some colorful insects, and sent this email, “What are these? I noticed a group of about 50 of these beauties on a saw-tooth oak in late spring 2019. I likely would have overlooked one as they are only about 1/2 the size of a grain of short grain rice. some of them have a horn-like protrusion on the head and others don't. [I am] assuming [a] male- female [difference]. They did not appear to be able to fly with the wings that some had. I assume they may be juvenile. I was so amazed at their size and beauty. Thanks for your help in identifying them.”

Dr. Sebe Brown, an insect specialist with the AgCenter, identified this insect, “Those are oak treehoppers (OTH). They’re cousins to three-cornered alfalfa hoppers in soybeans.” The University of Florida reports only minor damage by OTH, “Damage by a colony of this species of treehopper is minor and essentially confined to small oviposition [or egg laying] scars in twigs.” Because the damage is light, no treatments are needed.

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A tomato plant with southern bacterial wilt.
Photo: Dr. Don Ferrin.

Tomato plant with southern bacterial wilt

Richard sent in a soil sample to the Plant Diagnostic Lab (PDL) because his tomatoes were wilting, and he suspected soil-borne disease. Dr. Raj Singh, the AgCenter’s “Plant Doctor” confirmed Richard’s suspicion, “The soil from tomato bed tested positive for southern bacterial wilt [SBW] caused by Ralstonia solanacearum. It is a soil-borne bacterial pathogen and may survive in contaminated soils for several years. Prevention is the key in reducing the disease spread to new un-infected sites.”

Dr. Singh also shares these recommendations for managing SBW:

  • There are no effective chemicals registered to manage bacterial wilt.
  • Avoid fields with previous history of bacterial wilt.
  • Rotation with non-host crop, such as corn, beans, and cucurbits for 2-3 years, reduces bacterial population. [Cucurbits include cucumbers, squash, watermelons and other “viney” vegetables.]
  • Soil solarization of contaminated fields during summer may help in reducing the initial population of bacterium in the soil.
    • [The solarization process involves covering the ground with a tarp, usually a transparent polyethylene cover, to trap solar energy. The sun heats the soil to temperatures that kill bacteria, fungi, insects, nematodes, mites, weeds, and weed seeds. Source: Texas A&M Agrilife Extension]
  • Plant in well-drained, fertile soils.
  • Plant on raised beds and use plastic mulch bed covers.
  • Growers must follow good sanitation practices to reduce the spread of the disease including avoiding movement of infested soils, avoiding movement of stakes from known infested sites to new sites and proper cleaning of tools.

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Ooze test showing bacteria streaming from an infected stem. Photo: Richard Raid, University of Florida


Bacteria streaming from an infected stem

Richard sent a soil sample to PDL in Baton Rouge for a diagnosis. However, home gardeners can do a diagnostic test at home called the “ooze” test if they suspect SBW. According to the LSU AgCenter’s website, “The [home] test does not require any type of magnification; it only requires a clear drinking glass or small jar, clean water, and a sharp blade. A cross section through the symptomatic tissue is made, followed by suspending the tissue in water for 30 seconds to 1 minute.” Toothpicks are handy for suspending a plant stem in water.

If your plant is infected with bacteria, then then the bacteria will stream a white ooze as shown in the image. Viral infections and fungal infections will NOT stream like a bacteria infection will. The ooze test can also be a science experiment for school children studying at home.

If the ooze test comes out “positive” for SBW, then Dr. Singh’s treatment recommendations listed above will help gardeners have a productive garden despite SBW.

If you want to contact Roots, Shoots, Fruits and Flowers, please send your questions and pictures to Keith Hawkins, Area Horticulture Agent (AHA), 337-463-7006 or khawkins@agcenter.lsu.edu. Also, you can be on the “green thumbs” email list by emailing your request to the address above.

“This work has been supported, in part, by the USDA National Institute of Food and Agriculture, Renewable Resources Extension Act Award, Accession Number 1011417.”

4/7/2020 6:45:33 PM
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