Why oaks aren’t pruned in spring and early summer
Oak wilt has been found in Ontario. Timing your oak pruning is the simplest way to avoid helping it spread.
If you have an oak, the season matters more than it does for most trees. The advice is simple: don’t prune or wound oaks from April through July.
What oak wilt is
Oak wilt is a fungal disease that blocks the water-conducting tissue of oaks. It has been confirmed in Ontario. Trees in the red oak group, such as red and black oaks, are the most vulnerable and can die quickly once infected. White oaks are more tolerant but can still be affected.
How it spreads
- Beetles to fresh wounds. Small sap-feeding beetles carry the fungus from infected trees and are drawn to fresh cuts and wounds on oaks in the warm months.
- Root to root. Oaks growing near each other can share connected roots, which lets the disease move between neighbouring trees.
- Moving wood. Infected oak firewood can carry it to new areas.
When to prune oaks
Plan oak pruning for the dormant season, from late fall to late winter, when the beetles aren’t active. Avoid pruning or wounding oaks from April through July. If you can wait, wait for the dormant season.
For oaks, the season matters. Prune in the dormant season, and avoid April through July.
If an oak must be cut in summer
Storm damage and hazards don’t follow the calendar. If an oak has to be cut during the risk period, the fresh wounds should be covered right away with a wound dressing. For most trees wound paint isn’t needed; oaks in the warm months are the exception. The same goes for accidental wounds, such as bark damaged by equipment or roots cut during construction.
Signs to watch for
An oak with oak wilt often shows leaves wilting and turning brown or bronze from the edges inward, starting near the top of the crown, with leaves dropping in summer. Other problems can look similar, so the cause needs checking. Suspected oak wilt in Canada can be reported to the Canadian Food Inspection Agency.
Don’t move oak firewood, and buy firewood locally.
Oaks and oak wilt, in five lines
- Oak wilt has been confirmed in Ontario.
- Beetles carry it to fresh cuts in the warm months.
- Don’t prune or wound oaks from April through July.
- If an oak must be cut then, cover the wounds right away.
- Don’t move oak firewood, and report suspected cases.
This is general information. Every tree and site is different. For advice on a specific tree, get a free quote or book a Certified Arborist Assessment.
Jason Korkidakis
Jason is Koala Tree’s Owner and Lead Arborist in London, ON. He leads an 8-person crew and assesses trees for homeowners, condo boards and property managers.
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Learn moreHave an oak that needs work?
Get a free quote to schedule it in the dormant season, or book an assessment if you’d like Jason to look at the tree first.
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