In last week’s blog post, we went over what Oak Wilt is. Now, we’ll discuss oak wilt management. There are three primary approaches to oak wilt management that are used in Central Texas. Successful control usually depends on incorporating measures from all three approaches. The first approach attempts to prevent the formation of new oak wilt infection centers by eliminating diseased red oaks, handling firewood properly and painting wounds on healthy oaks so they don’t get infected in the first place. The second approach involves trenching or other measures which disrupt root connections responsible for transmission of the pathogen. Finally, injections of the fungicide propiconazole into individual, high-value trees help reduce crown loss and may extend the life of the tree. These measures do not cure oak wilt, but they can significantly reduce tree losses.
Preventing new infections
Infected oaks that die in late summer, fall or early winter should be cut down and burned, buried or chipped soon after discovery to prevent fungal mats that may form on these trees the following spring. If this is not possible, you should inject the trees should be injected with herbicide or deeply girdled with an ax and stripped of bark 2 to 3 feet above the soil line. Drying of the wood before spring also discourages the formation of fungal mats.
All wounding of oaks, including pruning, should be avoided from February through June. The least hazardous periods for pruning are during the coldest days in winter and the extended hot period in mid-to-late summer. Regardless of the season, all pruning cuts or other wounds to oak trees, including freshly cut stumps and damaged surface roots, should be treated immediately with paint to prevent exposure to contaminated insect vectors. Any type of paint will suffice.
Care should also be taken when transporting unseasoned firewood from diseased oaks. There is a slight potential to transport the oak wilt fungus. Oak wilt cannot be transmitted by burning diseased firewood. However, fungal mats may form on wood that is kept in storage. Never store your firewood near your oak trees just to be safe. Your best bet is to purchase wood that has been thoroughly dried for at least one full year.
Stopping spread of Oak Wilt through the roots
Measures can be taken to break root connections between live oaks or dense groups of other oaks to reduce or stop root transmission of the oak wilt fungus. The most common technique is to sever roots by trenching at least 4 feet deep with trenching machines, rock saws or ripper bars. Trenches more than 4 feet deep may be needed to assure control in deeper soils.
Correct placement of the trench is critical for successful protection of uninfected trees. There is a delay between colonization of the oak wilt fungus and the appearance of symptoms in the crown. You should carefully identify all infected trees first. The trench should be placed a minimum of 100 feet beyond the symptomatic trees even though there may be ‘healthy’ trees at risk of infection in the trench. Trees within a 100 foot barrier, especially those without symptoms, can be uprooted or cut down and removed to improve the barrier. If you must remove any trees, it’s best to do so after the trenching has been done. You start with healthy trees adjacent to the trench and gradually move inside the trench to include the symptomatic trees. Oak wilt infection centers are best suppressed when detected early, before they become too large. You will want to monitor your trees for several years at least.
Propiconazole is the only fungicide that has been scientifically tested and proven effective for use as a preventative treatment to protect live oaks. It also has limited success with trees that are treated with therapeutic injections during the earliest stage of infection. You inject the fungicide into the tree’s water-conducting vascular system through small holes that are drilled into the root flares at the base of the tree. Treatment success depends on the health of the candidate tree, application rate and injection technique. It’s best to have an experienced hand do the injections. Fungicide injection doesn’t stop root transmission of oak wilt so you should do this in conjunction with trenching or to protect high-value trees that you can’t trench.
For more information on managing oak wilt, we encourage you to call us at Austin Tree Service. Our phone number is 512-341-8888. Thank you.