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Bacterial Leaf Scorch Testing

August 29, 2006
The U of I Plant Clinic will be testing trees for Xyllella, the pathogen that causes bacterial leaf scorch (BLS) of trees. Common lab procedures to detect bacteria, such as sectioning and culturing, do not work with this one. We need to assay with ELISA (enzyme-linked immunosorbant assay). The clinic runs this particular ELISA only in the fall. If you have a suspect tree, send a sample in for testing. We will run assays the last week in August and the first week of September at the normal clinic fee of $12.50. We can accept only Illinois samples at this time.

How do you know if your tree may be infected? Refer to issue no. 14 of this newsletter, “Scorched Trees, a Closer Look.” Large trees that have healthy leaves each spring, develop scorched foliage by midsummer, and seem to be getting worse each year are most suspect. Infected trees show scorching weeks before surrounding trees begin to dry down in the fall, as seen in the image of an infected pin oal surrounded by healthy trees.

Careful examination of the trunk a few inches belowground does not reveal girdling roots. Some possible tree hosts include pin, red, scarlet, bur, white, willow, and shingle oaks; silver, sugar, and red maples; sweetgum; sycamore; planetree; hackberry; American elm; and red mulberry. For more information on symptoms, as well as plenty of images, go to this site by the National Arboretum: http://www.usna.usda.gov/Research/BacterialLeafScorch.html.

How do I prepare a sample for testing? We are going to grind the sample and extract plant sap to use in the ELISA.

For this reason, we need live plant material showing symptoms. Send three branch tips, each about 3 inches long, with all the leaves attached. Flatten and place these in a zip-lock plastic bag, labeled with the tree species and the words “for BLS testing.” Enclose a completed specimen data form (http://plantclinic.cropsci.uiuc.edu/hortdf.pdf) and your check payable to the University of Illinois for $12.50. Send by overnight express or one-day service to Plant Clinic, 1401 W. St. Mary’s Rd, Urbana, IL 61802. Call (217)333-0519 if you have questions.