If your oaks need pruning, the heat in July and August presents a good opportunity to do that while protecting them from oak wilt.
Oak wilt is a deadly fungal disease that can affect all oaks. In San Antonio landscapes, live oaks and red oaks are particularly susceptible.
While many methods have been developed to treat the disease, there is no cure. The beetles carrying it can fly up to a mile from any infected tree.
Since pruning oaks can spread oak wilt, the pruning season for live oaks and red oaks is limited, especially between Feb. 1 and July 1 when the fungus is most active. However, the form of fungus that spreads the disease (and the beetle that transports the spores of that fungus) are nearly non-existent in the latter half of summer — providing a brief pruning window over the next few weeks.
Although oak wilt slows down in summer, never let your guard down. When pruning oaks, always follow these rules to ensure proper pruning and prevent oak wilt:
- In the City of San Antonio, a contractor doing tree work is required to have a city-issued tree maintenance license.
- Paint all cuts and wounds on oak trees within 30 minutes. Any oil or latex based paint is appropriate. Be creative. Use different colors. Mix and match with the house.
- Always keep tools sharp and clean them with fungicide (Lysol, for example) between trees.
- To promote healthy wood and minimize damage, only remove dead, damaged, diseased and dangerous branches, especially in summer. For drought-stressed trees, avoid excessive pruning and leave some low branches to shade the trunk.
- Large branches (greater than 1 inch) should be undercut to minimize additional damage and help the wound heal faster.
- Remove any red oaks that have been identified with oak wilt.
Know where your firewood comes from. Beware of unseasoned firewood from diseased red oaks, which may contain oak wilt fungal mats.
Pruning in summer can mitigate some of the risk of oak wilt. If you miss the brief opportunity, winter is the next best time for oak pruning. (In fact, winter is normally the best time to prune any tree — except for those like redbud and Texas mountain laurel that flower on new wood in early spring.)
Consult with a certified or licensed arborist before doing any major pruning and follow their recommendations. The San Antonio Arborist Association or the International Society of Arboriculture offer member lists. They can help identify oak wilt and other issues that can affect stressed trees.
