Plan to prune now

January is an excellent time to finish oak pruning.

Oak wilt poses an ongoing threat to the majestic oak trees that grace San Antonio landscapes. This vascular disease — caused by the fungus Bretziella fagacearum (formerly Ceratocystis fagacearum) — disrupts a tree’s water-conducting vessels, ultimately leading to decline and death. For oaks, January is the season to finish up any pruning – because it’s the time when oak wilt spread is at its slowest.

Any oak tree can be susceptible to oak wilt, but red oaks are some of the worst affected, with mortality occurring in as little as 2-6 weeks. In addition, local live oaks are very vulnerable due to their often interconnected roots, allowing fungus to spread underground from tree to tree.

While oak wilt is very serious and can be transmitted year-round, the risks diminish during winter in south-central Texas when sap-feeding beetles that carry the fungus are less active. This reduction creates a narrow window for tree pruning in late fall and right now in January.

When in doubt, call a licensed arborist to assist as they have the tools and training to safely remove limbs where dangerous situations may exist.

Always adhere to these steps and precautions to prevent unintentional disease transmission when pruning oaks:

  1. Thoroughly disinfect pruning tools between cuts using a solution of 10% bleach or Lysol.
  2. Prune during dry weather to minimize the attraction of beetles to fresh wounds on the trees. They feed on the oozing sap a tree exudes.
  3. Immediately paint any cuts with tree wound dressing or latex-based paint. Paint after each cut is made and before the next cut is initiated.

Of course, fluctuating temperatures can occasionally create conditions conducive to beetle activity — even in winter — so always use caution. By February, beetles are expected to become very active; many localities and neighborhoods prohibit any tree pruning in spring, from February to June.

Understanding oak wilt, its transmission and the seasonally varying risk factors is essential for effective tree management in San Antonio.

By adopting proper procedures, including tool sterilization, careful timing and responsible disposal of pruned material, you can do your part to prevent the spread of oak wilt, safeguarding the health and longevity of San Antonio’s cherished oak canopy.

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Seth Patterson
A naturalist by nature, Seth spent his early childhood crawling through creeks and caves of the Hill Country before moving to South Texas where he found his passion in nature photography. Now an avid scuba diver and underwater photographer, Seth follows the water wherever he lands and truly takes to heart his role as a conservation consultant for San Antonio Water System.
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