Free Testing for Oak Wilt and Leaf Scorch in Missouri

By Blake Jackson

The University of Missouri (MU) Extension’s Plant Diagnostic Clinic, in collaboration with the Missouri Department of Conservation (MDC), will continue offering free testing for common oak tree diseases throughout 2025.

“We had a great season in 2024 as we received a total of 93 oak samples and diagnosed diseases including oak wilt, bacterial leaf scorch, tubakia leaf spot, anthracnose, cicada damage and so on,” said Peng Tian, director of the Plant Diagnostic Clinic on the MU campus.

“This allowed us to monitor the prevalence of the common diseases currently in Missouri and scout for new or invasive diseases of oaks to better assist MDC and the Missouri Department of Agriculture with controlling forest pest problems,” Tian added.

“With this service, we hope to continue collecting information on the location and host species of oak diseases across the state and monitor the tree health of the state.”

Oaks dominate both urban landscapes and forested areas across Missouri. Two of the most serious threats are oak wilt and bacterial leaf scorch.

Oak wilt can kill red oaks within weeks, while bacterial leaf scorch is a progressive disease that can take five to eight years to kill a tree. Both can spread to nearby oaks.

Oak wilt symptoms in red oaks usually appear in late spring or early summer, with leaves wilting, browning at the edges, and falling from the top of the tree downward. White oaks show similar symptoms later in the summer and may develop isolated dead branches over multiple years.

Bacterial leaf scorch blocks water and nutrient movement within the tree. Its symptoms can resemble drought stress, making lab testing essential for confirmation.

Tian advises anyone suspecting these diseases to submit samples for analysis. Start by sending 3-5 photos both close-ups and wider shots through the clinic’s digital submission system. Fees listed on the clinic’s website will be waived for oak disease tests.

For bacterial leaf scorch, collect 20-30 symptomatic but still-green leaves with stems attached, sealed in a plastic bag with a damp paper towel, and kept cool.

For oak wilt, include 20-30 leaves plus 4-6 live branch segments, 8-12 inches long and 0.5-1.5 inches in diameter. Keep samples cool but never frozen, and contact the clinic for specific shipping guidelines.

Photo Credit:pexels-vladimirsrajber