Key to decreasing Oak Wilt spread
From the Texas A&M University system comes news that the Texas Forest Service is encouraging Texans to be careful when collecting and purchasing firewood at this time of year.
Transporting and storing diseased wood is a known means of spreading the devastating oak wilt fungus to previously uninfected neighborhoods. Utilizing these prevention steps is the key to safeguarding against spreading the disease through the selection and use of firewood:
Select well-seasoned firewood. Well-seasoned wood is cut before the summer and is typically dry with loose bark and cracked ends. Avoid oak wood that appears unseasoned, that may have tight bark and cut ends which show no cracks or signs of aging. The extreme heat and drying of a full Texas summer effectively destroys the fungus in cut firewood.
• Safely store unknown sources of firewood. If the oak wood comes from an unknown source and it is not well seasoned, cover the woodpile with a clear piece of plastic. Burying the edges of the plastic will prevent the entry or exit of insects that might have been attracted to diseased wood and fungal mats.
• Destroy diseased red oaks. A knowledgeable arborist or forester should diagnose red oaks (i.e., Spanish, Texas red, blackjack or shumard oak) that die rapidly (2-3 weeks) or in groups (2 or more trees over several years) for oak wilt. Trees suspected to have died recently from oak wilt should be destroyed by burning, burying or chipping. The heat of a fire destroys the fungus and the smoke emitted poses no threat to healthy trees. Red oaks that have died from oak wilt should not be stored or used for firewood. When planning to do any outdoor burning, be sure you check with local officials to see if an outdoor burning ban is in place for your county and take care not to burn on windy days with low humidity.
• Avoid wounding oaks during vulnerable seasons. The general recommendation is to avoid injuries to oaks from February through June. The best times for pruning of oaks are during the heat of summer (minimal spore production) or the cold of winter (minimal insect activity).
• Paint all oak wounds including pruning cuts. Throughout the year, immediately apply a thin coat of latex or pruning paint to all fresh wounds and other injuries that expose the inner bark or sapwood of oaks. This prevents contaminated sap beetles from infecting the wound with oak wilt spores.
Oak firewood is an important commodity to Texans, whether it’s used for firing up the barbecue pit or for warming up the home on a cold winter’s day. By selecting well-seasoned, disease-free firewood and by following other disease prevention guidelines, homeowners are taking the correct steps to prevent a new oak wilt disease outbreak in their neighborhood.
For more information, visit www.texasoakwilt.org or call Jim Houser, TFS Coordinator for Oak Wilt at 512-339-4589.
1. What is oak wilt?
Oak wilt is one of the most destructive tree diseases in the United States. The disease has killed more than one million trees in Central Texas. Oak wilt is caused by the fungus Ceratocystis fagacearum. The spores of the fungus invade and clog the tree’s water conducting system, called xylem.
2. Will my oak trees get oak wilt?
All oaks are susceptible, but white oaks are the least susceptible. Very few have been identified with oak wilt in Texas. They generally survive for a number of years with the disease. Common White Oaks - Post, Bur, Chinkapin, Monterrey.
Red oaks are the most susceptible. They typically die within two to four weeks of symptom appearance. Common red oaks are Spanish, Texas, Shumard, Pin and Blackjack.
Live oaks die in the greatest numbers, most often in expanding areas called Oak Wilt Centers.
3. How does oak wilt spread?
Oak wilt is spread by two methods, root transmission and by sap-feeding (Nitidulid) beetles. The fungus spreads from tree to tree through connected roots, either by root grafts or through a common root system.
4. How quickly can oak wilt spread?
Because live oaks tend to grow from root spouts and can form root grafts very readily, all of the live oaks within a given area share a common root system. The pathogen can spread through this system at an average rate of 75 feet per year.
5. How can I treat my trees if they have oak wilt?
There are two main recommendations that are generally given to treat oak wilt infection areas:
A. Stopping the spread through the roots
Measures can be taken to break root connections between live oaks or dense groups of red 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, rocksaws or ripper bars.
B. Fungicide treatment
The fungicide propiconazole (Alamo) can be used as a preventative to reduce oak wilt symptoms in live oaks when applied before infection. Limited success may also be achieved in trees with therapeutic injections during the earliest stages of infection. The fungicide is injected into the tree’s water-conducting vascular system through small holes drilled into the root flare at the base of the tree.
Treatment success depends on the health condition of the candidate tree, application rate, and injection technique. Injection should be done only by trained applicators. Fungicide injection does not stop root transmission of the fungus. This treatment, therefore, is used best in conjunction with trenching or to protect individual high-value trees in situations where trenching is impractical.
More information at www.texasoakwilt.org