Question of the Week: November 30, 2017

“Neil, when is it OK to prune our live oak trees? I hear there are times when we shouldn’t prune.”

You’re probably referring to the oak wilt fungus that has been killing live oaks and other oak species for decades. It’s not a reason to avoid planting oaks, but it does give us reason to be cautious in how and when we prune our trees.

Oak wilt is spread in several ways. One of them is via insects that invade open wounds made by pruning tools.

Photo: Mature live oaks are often pruned by skilled arborists to keep them from rubbing rooftops, also to lessen likelihood of limbs breaking in wind, ice or snowstorms. Sometimes people will have them pruned to get more light to plants beneath them, but that will often need to be redone every year or two as the trees continue to grow. This pruning must be done at the right time and in the right way.

Here’s how to prune oaks…
Veteran pathologists and foresters give us these guidelines to pruning oaks:

Prune only while the oak wilt fungus is inactive. That certainly includes mid-winter (Thanksgiving until Valentine’s Day). But more recent research found that you can also prune from mid-summer on. So the OK time is July 1 through January 31. The time to avoid is February 1 through June 30 (think “springtime”) – while oak wilt’s fungal mats are active in infected trees.

Make cuts almost completely flush with the trunk or with another branch. Leave a short section of branch collar for quickest healing.

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Coat all cuts as large as your thumb with black pruning sealant to keep insects from entering.

Photo: This recently pruned branch should be treated immediately with pruning sealant. Photo borrowed from Texas Oak Wilt website.

Disinfect pruning tools with a 10-percent solution of chlorine bleach or Lysol between every cut.

If you’d like to read the whole story about oak wilt and its suppression, here is the fine website from the Texas Oak Wilt Coalition.

Posted by Neil Sperry
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