COLUMBIA, Mo. – University of Missouri Extension’s Plant Diagnostic Clinic, in partnership with the Missouri Department of Conservation (MDC), will offer free testing for all common oak tree diseases in 2024.
“With this service, we hope to collect information on the location and host species of oak diseases across the state,” says Peng Tian, director of the Plant Diagnostic Clinic on the MU campus. “We are also actively scouting for new or invasive diseases of oaks to better assist MDC and the Missouri Department of Agriculture with controlling forest pest problems.”
Oaks are the most abundant trees in yards and forests across Missouri. Two common oak diseases are bacterial leaf scorch and oak wilt. Oak wilt weakens white oak trees and kills red oaks within weeks of infection. Bacterial leaf scorch is a chronic disease that worsens over several years. Both diseases spread to nearby oaks.
Oak wilt symptoms first appear in late spring or early summer in red oak. Leaves discolor, wilt and fall, first at the top of the tree and later at the tips of lateral branches. Leaves turn a dull, bronzed brown at the tips and along the outer margins. Similar symptoms appear in white oak trees in mid-to-late summer. Trees infected for two or more years commonly develop isolated dead branches in the crown.
Bacterial leaf scorch infects the xylem of susceptible trees and prevents water and nutrients from being transported. There is no cure for bacterial leaf scorch on oak, and trees die within five to eight years. Symptoms are similar to drought stress and can only be diagnosed by laboratory analysis.
If you suspect either disease in your trees, Tian recommends sending samples to the clinic for testing and confirmation.
You may first send three to five photos to the clinic. Go to https://mizzou.us/PDC-DSF for instructions on submitting photos online. Tian suggests submitting both close-up photos and photos from a distance. MU Plant Diagnostic Clinic staff will contact you about submitting physical samples, depending on the tree health problems observed in the photos.
For bacterial leaf scorch testing on oaks, select leaves that are still green but show leaf scorch symptoms, says Tian. Collect 20-30 leaves with the petiole (leaf stem) attached and pack them in a sealed plastic storage bag with a damp paper towel. Keep the leaves cool. Contact the lab about shipping recommendations.
For oak wilt testing, collect four to six branch sections that are about 8-12 inches long, roughly 0.5-1.5-inch in diameter and alive but showing symptoms of leaf wilt.
Keep the samples cool, but do not freeze them, says Tian. Samples that get hot during transit to the lab may not test positive for the fungus. Contact the lab about shipping recommendations and timing.
For more information on sample submission, visit the MU Plant Diagnostic Clinic website at http://muext.us/PlantClinic The clinic is at 28 Mumford Hall, 1100 University Ave., Columbia, and is open 9 a.m.-4 p.m. Monday to Friday.
