Talk:Oak wilt

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WAGING WAR ON OAK WILT

Article Written by: Maggie Ambrosino, Certified Arborist Owner of Brown and Green Tree Consultants, Austin, Texas

Skeletons of dead oaks, standing gruesome and gray, are common sightings along the landscape and, closer to home, our neighborhood streets and parks. These images are far too haunting to ignore their existence. Many of our once grand oaks are now canopies of sparse and riddled decline, existing to the point of asset vs. liability—and many of the dead are left standing in testament to a dreadful disease too long ignored. Our live oaks are worth saving. Our live oaks are worth protecting. What other trees grace us with their 100-foot canopies of cool, sweet shade, and waylay against our harsh eco system to showcase their majesty for generations of beauty and enjoyment? The battle against oak wilt is far from over, and the fungal disease continues to progress approximately 80 feet per year. A contaminated oak can infect healthy adjacent oaks underground up to 200 feet away. Knowing what we now know, or should know, about oak wilt—that it is one of the most destructive tree diseases in the United States and the lethal fungus, ceratocystis fagacearum, spreads and kills in epidemic proportions by invading and disabling the water-conducting vessels in vulnerable trees—it is evident that pruning oaks should be done with knowledge and vigilance. We also know that oak wilt is spread two ways: by insect vectors that land on fresh cuts or wounds, and through grafted root systems. By acting on what we do know, with due diligence, we can make great strides against the disease. How do we recognize oak wilt? Look for the telltale signs evidenced by leaf symptoms, patterns of spreading decline, tip die-back, rate of tree mortality and close proximity of other oak wilt centers. Out-of-season browning, leaf drop and veinal necrosis are also warning signs, but words of caution please: Obtain a professional diagnosis. These symptoms are not all strictly indicative of oak wilt, and oak wilt is not strictly limited to these symptoms. How do we further manage oak wilt? First and foremost, make wise and informed choices on how we prune our trees. The daily buzz of chain saws can seem more like open season than pruning season. When choosing an arborist, make sure they are certified. Ask for that ISA card (International Society of Arboriculture) and ask for insurance! The inability to prove-up such requests should cast doubt. Drive-thru businesses leaving door-hangers and pulling trailers are not always your certified best bet, and though their labor costs are attractive, the value of resistance has a payback in the long run. It is better to save one tree at a time, if that’s all the budget allows, rather than accept that rock-bottom price for substandard work and risk spreading the disease. Ensure all tools are sterilized. Do it between every tree. Use pruning sealant on those oaks—on every single wound—whether it is from a saw or weed-eater or lawn mower scuffs across a lateral surface root. Vectors, which transport the disease from tree to tree, love the fruity smell of sap oozing from a fresh wound. Pruning paint or sealant helps to mask that smell. Prune live tissue from July to the end of January or in the hottest of summer and coldest of winter. Avoid pruning in the spring when the insect population is high and roots are vigorous. The bulk of the infection is transferred below ground, through grafted roots. It is the healthy oaks, more so than the contaminated oaks, which warrant our attention and protection, and a tree that still retains at least 30% of its canopy deserves any and all attempts to restore its health and vigor. How do we engage in direct battle with oak wilt? We can fight toward its prevention and suppression. The key to success with oak wilt, as with any disease, is recognition and swift response. Have those valued oaks injected by a professional, licensed applicator with an oak wilt-specific fungicide, or propiconazole, and avoid ineffective broad-spectrum fungicides; trench at a sufficient width and depth to sever root systems in areas where streets or utility work has not already done the job for you; and remove, wrap, dispose of or burn dead and dying red oaks immediately and never store the wood for firewood. The white oak family, which includes live oaks, is vulnerable to the red oak family which produces the deadly fungal mats responsible for the spread of the disease. White oaks can show symptoms over many years. The red oaks die quickly and suddenly, harboring lethal fungal mats beneath the bark. If cut wood cannot be removed off-site immediately, it should be covered with a clear plastic tarp and the edges of the tarp buried below soil level. Lastly, if it’s oaks you love, consider diversifying your shade tree plantings to a more oak wilt resistant variety such as the burr oak, Monterrey or Mexican white oak, or chinquapin oak. There are also other natives and adapted species that are well worth considering. Unfortunately there is no complete cure for oak wilt. But there is a high rate of success in suppressing the disease and prolonging the life and beauty of our oaks for many more years to come if we remain as aggressive as the disease and, like our mighty oaks, hold our ground. For more information you may contact Maggie Ambrosino, 922-4649 or tjambro@sbcglobal.net, the Texas Forest Service, or check out these websites: www.isa-arbor.com/ www.texasoakwilt.org www.ci.austin.tx.us/oakwilt/ www.treetalkusa.com/