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Former Extension Educator, Horticulture
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Tuesday, November 18, 2014
Posted by Veronica Shaughnessy -
In October, I was lucky enough to have the opportunity to attend the Upper Midwestern InvasiveSpecies Conference in Duluth, MN. I found this conference extremely informative! Although it would be impossible to share all the information from the conference, I would love to share some things that I found particularly interesting in my next two posts.
Today, I would like to talk about Bur Oak Blight which is present throughout much of the Midwest and has been confirmed in Illinois as well. Although Bur Oak Blight, or BOB for short, has been confirmed in Illinois for several years now. BOB is a leaf blight disease caused by a species of Tubakia iowensis. True to its name, BOB is only found on Bur Oaks. The symptoms of BOB have a wide range of severity. However,The most severe symptoms have been found on the smaller acorn producing variety of Bur Oak, Quercus macrocarpa var. oliviformis. BOB is more likely to occur in trees located on upland sites.
Symptoms of BOB typically begin to show in late July or August. Symptoms include: purple or brown lesions on the midvein and large lateral veins on the leaf's underside. Over time, lesions will get larger and darkened veins become noticeable on the upper surface of the leaves. Eventually, leaves develop necrosis in wedge shaped areas or even full portions of a leaf may die.To check for the presence of BOB, look along the underside of the leaves with the assistance of a handlens. Black pustules will be present on the major veins during the summer and also on leaf petioles inlate summer. In the fall, Bur Oaks infected with BOB tend to hold on to their leaves. BOB infections increase in severity with time. Symptoms first appear on lower branches and move upward.
What to do?
Here is the good news: in order to cause tree mortality, a tree usually has to be infected for many years or have a secondary issue. Because BOB over winters on petioles left on the tree, BOB cannot be successfully managed with sanitation. Fungicides have had some success in the management of BOB. However, treatment is expensive and is only recommended for use in high value trees.
More information and photos can be found at: