Bur oak blight, (Tubakia iowensis sp. nov. – a subspecies of Tubakia) is a disease that causes petiole and leaf necrosis. The pathogen may have come from Europe or Asia but is potentially a localized mutation of Tubakia to the Midwest. This pathogen is a long term pest (the disease intensifies year after year) that requires many growing seasons to build a strong enough pathogen population to cause tree death. The pathogen has been positively identified in Iowa, Minnesota, Missouri, Arkansas, Illinois, and many other states believe they have the pathogen. However, the movement of the pathogen to new areas is relatively slow. It is possible that Bur Oak Blight requires a highly specific environment to develop and survive; which may prevent widespread pathogen distribution.
Due to the limited trial research available regarding this pest, much of this is based upon preliminary studies and the treatment of similar pathogens. A root flare injection to control the infection occurring in the petioles and leaves using Alamo fungicide is the most effective known treatment for Bur Oak Blight. Only 2/3 of Bur Oaks have shown a response to treatment with Alamo, the reason for this is not understood. Monitoring is crucial as much of the management is yet unknown. Bur oaks should also be treated preventively with Xytect insecticide to prevent against two-lined chestnut borer.
Cultural practices such as mulching trees in turf grass environments, regular watering, fertilization, or use of Cambistat to promote tree health can also help increase tree vigor and mitigate the impacts of Bur Oak Blight.
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Bur Oak Blight Treatment Option 1
Find out more about quick tips on oak wilt treatments.
Application Type – Low Volume Macro-Infusion
DIY Product/Equipment Needed:
• Shovel and hand trowel
• Stiff bristled hand brush
Bur Oak Blight Treatment Option 2
Cambistat®, a growth hormone regulator, has been shown to increase drought tolerance and vigor in trees with compromised root systems, a common predisposing factor for tubakia infections. By slowing top growth, energy is directed to roots, encouraging the development of an extensive, fibrous root system. In addition to increased drought tolerance, leaves are often smaller, greener and have a thicker waxy covering. Not only are these leaves more efficient in making “food”, they are less prone to foliar infections because the coating is more difficult to penetrate. Cambistat® is a soil applied product that lasts for three years in the tree.
Application Type – Soil drench
DIY Product/Equipment Needed:
• Measuring or diameter tape
• Graduated cylinder measuring in mL
• Bucket or watering can
How Is It Spread?
Black fruiting bodies develop in leaves that have been killed and remain on tree. They will develop in the fall/winter at the base of the petiole. In spring they are mature and spores from them will be splashed through rain onto new leaves. This makes the disease very severe because re-infection is so common
Bur Oaks (Quercus macrocarpa)
Leaves when they first leaf out appear healthy each year.
This is a late season disease with symptoms appearing in late July, August, and September. Veinal browning occurs in late summer. Leaves initially have brown spots that eventually coalesce resulting in complete leaf browning and leaf curling. New flushes of growth in September will be killed by the fungus as well. Leaves stay hanging on the tree through the winter, which is unusual for Bur Oaks. Petioles will hang on through summer. Infections typically start in the lower portion of the crown and spreads higher up in subsequent years.
Black fruiting bodies develop at the base of the petiole in the fall and infected leaves will hang on throughout the winter and early spring months. The black fruiting bodies (spores) are on the petioles that overwinter and hang on to the tree and these spores become the overwintering inoculum to infect the tree the following year in May/June.
Two-line chestnut borer can cause dieback in limbs, and is found in stressed trees; therefore, it may be in bur oak blight infected trees, along with the Tubakia pathogen.
Anthracnose looks similar, but works from the bottom up, and leaves do not persist like bur oak blight. Bur oak blight infected trees show browning on most leaves on entire branches. Leaves hanging on bur oak in winter are very distinctive of bur oak blight.
Two-lined Chestnut Borer (TLCB)
Spring through Summer
Risk of Spreading