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Bur Oak Blight

Michelle Grabowski, UMN Extension Educator

T. Harrington, ISU

Photo 1: Leaves killed by Bur Oak Blight clinging to the tree after fall leaf drop

A healthy bur oak will drop all of it's leaves in the fall. Leaves that are infected with the fungal pathogen (Tubakia sp.) that causes Bur Oak Blight (BOB) remain attached to the tree into the winter. As a result, now is a good time to examine landscape bur oaks for possible infection with BOB.

Bur Oak Blight causes leaves of bur oak trees to develop brown wedge shaped lesions in July and August. This fungal disease often starts in the lower canopy and progresses up the tree in following years. Some bur oak trees are highly susceptible to BOB. After several years of infection, the entire canopy can appear brown and scorched. These severely infected trees are weakened and often fall prey to secondary pests like two lined chestnut borer and Armillaria root rot. It is possible for bur oaks to be killed by this combination of fungal and insect attackers.

Bur Oak Blight was first identified in Minnesota in 2010. Since then BOB has been found in 20 Minnesota counties including Mille Lacs, Sherburne, Hennepin, Ramsey, Washington, Anoka, Wright, Dakota, Carver, Pennington, Beltrami, Pope, Lac Qui Parle, Ottertail, Stearns, Polk, Marshall, Mower, McLeod, and Morrison.

If you suspect your bur oak tree is infected with BOB, contact the University of Minnesota Plant Disease Clinic about how to submit a sample for diagnosis. For more information about BOB, read the USDA Forest Service Pest Alert about BOB.
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