Every time I enter my own driveway and see the once beautiful live oak tree on the right, completely void of leaves, whose life was snuffed out way too soon, I am reminded of the destructiveness of the dreaded but ever-present disease of Oak Wilt.
If you are like me, you get used to a particular tree on your property, the shade it provides, its beauty, a shelter for the birds. It is like losing a family member when it dies and you want to go into mourning.
This disease, in Texas, is robbing us of a precious natural resource - oak trees.
The fungus, Ceratocystis fagacearum, which clogs the water conducting vessels of infected trees causing them to wilt and die, causes Oak Wilt. It is considered to be one of the most destructive tree diseases in the U. S. According to Renee Burks with the Texas Forest Service, approximately 3000 trees have been lost to Oak Wilt in Somervell County alone. The types of trees that can get Oak Wilt are live oaks and red oaks (including Spanish oak and blackjack oak).
Oak Wilt can be spread in two ways:
* Underground, from one tree to another through connected roots, thus forming expanded patches of dead and dying trees. The rate of spread for live oaks is known to be about 75 -100 feet per year.
* 2) Above ground, from infected red oaks carry the Oak Wilt fungus to fresh wounds on uninfected oak trees.
For Oak Wilt to be introduced into an area several factors must exist. There must have been infected red oak wood in the area, which has produced the fungus spores. A nitidulid beetle (very small, black with yellow stripes) must land and feed on these spores (attracted by the fruity odor), then fly to a nearby tree which has a fresh wound; the beetle being attracted by the sap.
Symptoms of an infected tree are apparent first with characteristic patterns on the leaves: an out-of-season change of color. In live oaks, the veins on the leaf will turn yellow or brown, while the rest remains green. Occasionally there may be the reverse of this. Sometimes just the tips turn brown. It is noteworthy that a lightening strike can cause similar patterns. Leaf dropping occurs gradually as soon as the tree is infected and death could occur in 3 months to a year.
In red oaks, leaf symptoms are less distinct. Watch mainly for leaves quickly turning pale green to brown, still remaining attached to the tree for some time. Death occurs more quickly than live oaks. Once red oaks are infected, they will die within 2 weeks to a few months. Red oaks may also develop a dark gray, oblong fungal mat beneath their bark. The odor of the mat resembles that of rotting fruit. These mats are areas covered with spores, making the tree especially contagious. Fungal mats are not known to occur on live oaks and production of spores is accelerated by cool, moist weather.
We have found on our own property here in Somervell County that the key to possibly saving the tree is early detection and aggressive treatment. We have lost several trees, but we have also been able to save some and a few we are just waiting to see.
It is of utmost importance that any open wounds on your live trees are painted. The first 36 hours is critical, before the tree starts healing on its own. Pruning paint, even Elmer’s glue, or anything that will seal the wound to prevent infection should be used. It is believed that infected firewood, left unattended, has been the cause of the widespread disease, which has been noted in over 60 Texas counties. Cover with clear plastic, burn, bury or chip the cut red oak wood after pruning. The heat will kill the spores and the smoke will not aid the spread. It is important to disinfect all pruning tools between trees. Red or live oak root sprouts greater than 1/2 inch in diameter that have been cut down should also be sealed.
There are several options open to the landowner for treatment and /or prevention of Oak Wilt disease.
* Do nothing and hope the tree survives
* Trenching to attempt to stop the underground spread.
* Fungicide injections ( propiconazole)
* A combination of 2 and 3.
Trees with more than 30 percent canopy loss should not be treated. Once a tree is dead, it cannot support the fungus. Injection is mainly used to protect high-value oaks in advance that are within 50 - 150 feet from symptomatic trees. Although injections of fungicide have proven to be very effective, it does not prevent the spread of the fungus underground.
Gene Gehring, a Certified Arborist and owner of Urban Renewal, Inc. is an Oak Wilt Specialist. We have called on his services to inject 15 - 20 of our trees and it appears to have saved most of them. The key is early detection. At the first sign, usually when the leaves on the outside branches turn color, the tree should be injected. Even a few days could make a difference - and I speak from experience.
If an infected red oak is found, it should be brought down on the spot and the wood burned or covered with clear plastic in order to kill the spores and the beetles to prevent the spread of both.
In Southern history, live oaks were landmarks where people met to socialize and conduct business. In the opening scene of “Gone with the Wind” Scarlett O’Hara flirts with bachelors under live oaks at a barbecue. Similarly, Marjorie Kinnan Rawlings ends her book “ The Yearling” with the hero saying farewell to his childhood under the live oak trees. The USS Constitution got its name “Old Ironsides” for the strength of its live oak wood. Cannon balls bounced off its side in the War of 1812. Live oak wood is one of the most durable woods in the world. Its deep roots and relatively short stature help it to withstand strong winds thus providing protection to nearby structures. Lastly, red oaks and live oaks on your property provide beauty, shade, a home and food for wildlife and value.
Hopefully we can all work together to slow down this unfortunate malady that is altering the Texas landscapes.
More information and training about Oak Wilt Disease is available through the Texas Forest Service, Texas A&M University, www.texasoakwilt.org, and your Texas AgriLife- Extension Service.