COLUMBUS — Oak Wilt is a serious and often deadly vascular disease of oaks. The fungal pathogen, Ceratocystis fagacearum, is believed to be native to the United States and has been reported throughout the Midwest and Texas, including Ohio.
Which Trees Are Affected?
Oaks in the red oak group – Black Oak, Northern Red Oak, Northern Pin Oak and others with pointed leaf edges – are most easily infected by this disease. Oaks in the white oak group – White Oak, Swamp White Oak, Bur Oak and others with rounded leaf edges – are less susceptible.
What to Look For?
Leaves of oak trees usually begin withering in the upper canopy, producing “flags.” Flags are whole branches or crown portions turning red-brown. Leaves of red oaks typically show yellowing and browning of the leaf margins.
Control and Management of Oak Wilt Disease
To properly manage Oak Wilt, it is essential to understand its life cycle. The pathogen spreads from diseased to healthy trees in two ways: above ground and underground. The above ground disease is spread mainly by sap-feeding beetles, known as Picnic Beetles (Coleoptera: Nitidulidae), on fresh pruning cuts.
While insect spread is one mechanism for infection, it is estimated that 90% of new infections occur between neighboring trees through root grafts. It is essential that Oaks not be pruned during crucial months of disease transmission.
While the high risk of infection occurs from April-July, research states it is prudent to avoid pruning Oak trees from just prior to bud break to leaf drop. This means DO NOT PRUNE from April to November.
Avoid Wounding Oak Trees
New Oak Wilt sites have been traced to spring and early summer wounds from tree-climbing spikes, rights-of-way pruning, nailing signs on trees and accidental tree-barking; a wound created when the bark is removed via impact from equipment, falling trees and other causes.
If you suspect your Oak trees have this disease, the Ohio Chapter International Society of Arboriculture (ISA) recommends you work with an ISA Certified Arborist for diagnosis and treatment strategies.
What if you need to prune oak trees during the growing season?
Trees that must be pruned during the growing season, like storm damage, should be immediately treated with a tree wound dressing or latex-based paint to seal the wound.
It is imperative that the fresh wounds be treated immediately because the insects that carry spores of the pathogen are often attracted to these wounds within a very short time. Tree paints usually are not recommended for general use but using these products in this situation can help protect trees from oak wilt.
If whole trees are removed during the critical period, the stumps should also be treated with tree paint.
Over 1,000 Ohio Certified Arborists Ready to Help
There are over 1,000 qualified tree experts in the state of Ohio that have been designated by the ISA as Certified Arborists. These tree care profession have experienced rapid growth over the past decade and there is a significant amount of knowledge required to perform at the highest level. To find one in your area, visit www.treesaregood.org.
NOTE: The mission of the Ohio Chapter International Society of Arboriculture is to advance responsible tree care practices through research, technology, and education while promoting the benefits of trees.
