Oak wilt can attack suddenly and kill quickly. Trees can rarely be saved once they’ve been infected, but careful observation and good tree-care practices can reduce the chance of infection.
Here’s what you can do:
• Have your oaks inspected periodically by an arborist or tree-care company that’s familiar with oak wilt and knows whether other trees have been infected in your area. Some larger companies will inspect trees for free, said Gordon Matthews of the Davey Tree Expert Co.
• Don’t prune or otherwise wound oak trees from April through June, an active time for the picnic beetles that are the prime culprits in the spread of the disease. An even more conservative approach is to avoid pruning from April until early October, the Ohio State University Extension says.
Any wound is a potential entry point for the fungal spores that cause oak wilt, even damage from wildlife or nicks from lawn mowers or weed trimmers. So are the wounds from tree-climbing spurs, which are sometimes used by tree pruners who are less than knowledgeable, said Alan Siewert of the Ohio Division of Forestry.
Siewert said spurs should never be worn when a tree is being pruned, only when one is being felled.
• If an oak becomes wounded, immediately paint the wound with a light coating of latex spray paint. This is the one exception to the general rule against painting tree wounds, Siewert said.
Use a cheap paint that doesn’t contain rust inhibitors, he said. Don’t use an oil-based product, which can kill the cambium, a tissue layer below the bark. Apply just enough paint to color the wound, not seal it.
Siewert said it’s believed the paint masks the smell of fresh sap, which attracts sap-feeding beetles.
Don’t delay. If the wound is more than eight days old, he said, painting it won’t help.
• When you prune an oak tree, disinfect pruning tools such as chain saws and pruning saws afterward before using those tools on another oak. Siewert said any household disinfectant will work, such as Lysol or a bleach-water solution.
• If you hire someone to prune or work on your trees, Siewert recommended hiring an arborist certified by the International Society of Arboriculture or a company that has an ISA-certified arborist on staff. You can find an arborist on the association’s consumer website, www.treesaregood.com.
• If you suspect an infection, call in a reputable tree-care professional with experience in treating oak tree wilt. The company will evaluate the tree and determine whether treatment is worthwhile.
Treatment may involve injecting healthy trees with fungicide and possibly cutting trenches between trees to sever their shared roots. The OSU Extension recommends leaving those treatments to experienced professionals.
Those methods can be expensive, but Siefert said they may save trees that are worth thousands of dollar and provide shade that significantly reduces cooling bills.
• Diseased wood should be disposed of properly. If you want to use the wood for firewood, stack it in a sunny area and cover it with a 4-mil-thick, clear or black plastic tarp so the heat will kill the fungus.
Mend any punctures in the tarp with duct tape, weigh down the edges of the tarp on the ground and cover the edges with soil so beetles can’t get in and out.
Leave the tarp in place for at least a year, and don’t remove it till October, once the danger of spreading the fungus has passed.
More information is in the OSU Extension’s Oak Wilt fact sheet, found at http://tinyurl.com/oak wiltohio.
— Mary Beth Breckenridge