Ash and oak are two of the most familiar trees around the Roanoke Valley, and both face serious threats. For ash, it is the emerald ash borer, an invasive insect that has killed ash trees across much of North America. For oaks, the concern most homeowners can act on is oak wilt, a fungal disease spread in part by beetles attracted to fresh wounds. Knowing the symptoms and the timing rules helps you decide whether to treat, prune, wait or remove.
Emerald ash borer (EAB)
What it does
The Virginia Department of Forestry (DOF) describes EAB as an insect native to Asia whose larvae feed under the bark on the tree's vascular tissue, disrupting the flow of water and nutrients. DOF states that all native ash trees in Virginia are susceptible and that a healthy ash can be killed within a few years of the first symptoms.
Symptoms
- A thinning canopy, often starting at the top.
- Sprouts from the trunk (epicormic branching).
- S-shaped (serpentine) galleries under loose bark.
- Small D-shaped exit holes in the bark.
- Increased woodpecker activity in winter.
Treat or remove?
DOF says the most effective treatment is trunk injection with the insecticide emamectin benzoate, for trees with a live crown of at least 70 percent, and that these injections have been shown to protect trees for up to three years. Treatment is an ongoing commitment, so it makes most sense for healthy, valuable ash in good locations. Ash that is already heavily declined is usually a removal candidate.
Virginia DOF cost-share
DOF runs an Emerald Ash Borer Treatment Cost-Share Program. According to DOF's program page, it can cover up to 70 percent of the cost of emamectin benzoate stem injections, with eligible trees being native ash species at least 12 inches in diameter at breast height with no more than 30 percent crown loss, assessed by a DOF forester before enrollment. Payment caps and application windows apply; DOF listed an application window of April 20 to June 18 for 2026. Check DOF's page for the current year's terms and contact your local DOF forester.
Why dead ash should not wait
Dead ash dries out and becomes brittle, which makes it more likely to drop limbs or snap, and more dangerous for climbers. Removal may require a bucket truck or crane rather than climbing, which can cost more. If you have dead ash near a house, driveway or road, put it near the top of the list. Do not move ash firewood long distances; DOF and other agencies warn that moving wood spreads pests. See tree removal.
Oak wilt
What it is
Oak wilt is a fungal disease. Extension sources describe how sap-feeding beetles carry spores to fresh wounds on oaks, and how infected trees can pass the disease to nearby oaks through connected roots. Trees in the red oak group (pointed leaf lobes) are especially susceptible; the white oak group (rounded lobes) is less so.
Pruning timing
Virginia Cooperative Extension's deciduous pruning calendar marks oaks for dormant-season pruning, and Extension-affiliated Master Gardener guidance recommends November and December and avoiding pruning from March through August. If an oak must be pruned in the growing season because of storm damage or a safety hazard, that guidance suggests sealing the wound. This is one of the few cases where wound dressing is advised.
Symptoms
Rapid leaf loss in summer with wilting starting at the top, especially in red oaks. Confirming oak wilt requires lab testing; many other problems, including drought, root damage and other diseases, can look similar.
Other oak decline
Many declining oaks in the valley are suffering from root damage, soil compaction, grade changes from construction, or drought stress rather than a specific disease. An arborist assessment helps distinguish them.
What we recommend
- Identify your ash trees and decide early whether any are worth treating.
- Remove dead ash near targets promptly.
- Schedule oak pruning in the dormant season.
- Get declining oaks assessed before deciding to remove.
Sources
- Virginia DOF, EAB Treatment Cost-Share Program: https://dof.virginia.gov/forest-management-health/forest-health/financial-assistance-program/emerald-ash-borer-treatment-program/
- Virginia DOF, Deadly Jewels of Virginia Forests: https://dof.virginia.gov/deadly-jewels-of-virginia-forests/
- Virginia DOF, DOF Can Help Protect Your Ash Trees: https://www.dof.virginia.gov/dof-can-help-protect-your-ash-trees/
- Virginia Cooperative Extension, Deciduous Tree Pruning Calendar (pub. 430-460)
- Piedmont Master Gardeners, Timing of Pruning Oak Trees: https://piedmontmastergardeners.org/timing-of-pruning-oak-trees/
Common questions
Can an ash tree with emerald ash borer be saved?
Virginia DOF says trunk injection with emamectin benzoate is the most effective treatment for trees with at least 70 percent live crown. Heavily declined trees are usually removed.
When should I prune oak trees in Virginia?
Extension guidance favors the dormant season, with November and December recommended, and avoiding March through August.
Does Virginia help pay for ash treatment?
DOF runs a cost-share program covering up to 70 percent of eligible treatment costs, subject to eligibility rules, caps and an annual application window.