Bur oak blight, (Tubakia iowensis) 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 this pathogen requires a highly specific environment to develop and survive; which may prevent widespread pathogen distribution.
Bur oak blight should be managed using a tool box approach. Alamo macro-injections will suppress disease symptoms and soil applications of Cambistat will suppress disease symptoms, improve fine root development, drought tolerance and overall tree health. Preventive insecticide treatment of Transtect or Xytect should be applied to manage two lined chestnut borer and other secondary insect pests. Mectinite can also be applied as a tree injection treatment for protection against two lined chestnut borer for tree injection situations.
In addition, practices aimed at improving the soil and root environment should also be considered to improve the overall health of oak trees. These practices would include the use of the air spade to alleviate compaction, prescription fertilizer and application of organic matter or other soil amendments. Preliminary results have shown that this approach will yield the best results to date.
Other Treatment Practices
- Practices aimed at improving the soil and root environment should also be considered to improve the overall health of oak trees. These practices would include the use of the air spade to alleviate compaction, prescription fertilizer and application of organic matter or other soil amendments.
- Remove fallen leaves throughout the year underneath the canopy to help reduce the amount of inoculum present for reinfection during the spring time.
- If applying Mectinite for two lined chestnut borer, use the same drill holes or tank mix.
For best results both Alamo and Cambistat should be applied in most treatment strategies. In addition, a preventive insecticide treatment of Transtect or Xytect should be applied to manage two lined chestnut borer and other secondary insect pests. Recent research has shown that Alamo treatments applied at bud break significantly reduce any chance for leaf phytotoxicity. Alamo applications made after full leaf out may result in greater phytotoxicity and leaf defoliation. Longer uptake time (up to a few hours or more) for Alamo applications can be experienced on treatments made during bud break. To alleviate this use multiple tanks and harness set ups to set up and treat multiple trees on site at once.
Signs of Damage
- 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. 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
Trees At Risk
- Bur Oak (Quercus macrocarpa) only
- 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.
Harrington, Thomas., Mcnew, Doug., Yun, Hye Young. “Bur oak blight, a new disease on Quercus macrocarpa caused by Tubakia iowensis sp. nov.” Mycologia. 104(1), pp. 79-92, 2012.
Harrington, Thomas. Personal Communication., 2012
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