Prune oak trees now to protect against spreading disease called oak wilt

January 17, 2017
oak wilt

Symptoms of oak wilt. Photo courtesy Joseph OBrien, USDA Forest Service, Bugwood.org

Pruning oak trees in winter can help protect the oaks from becoming infected with oak wilt, a fungal disease that can be deadly for oaks, according to the New York State Department of Environmental Conservation.

The disease was discovered in six new locations in New York State last year and can be spread by beetles that are attracted to freshly cut or injured trees.

Benefits of winter pruning:

  • Diseases are rarely spread during this time, since insects and fungi are inactive.
  • A tree’s branch pattern and damaged limbs are easier to see without leaves.
  • Leafless cut branches are lighter and easier to carry.
  • Nearby plants are less likely to be damaged by falling branches and trampling.
  • Removing weak and damaged branches before heavy snowfall reduces additional breakage.
  • Trees pruned in winter respond more vigorously in the spring, putting out new growth.

How does oak wilt spread and kill trees?

The oak wilt fungus clogs the trees’ transport vessels, cutting off water and food from leaves and the rest of the tree. One way oak wilt spreads is when fungal spores hitch rides on insects. Sap beetles, one of the main culprits, are extremely attracted to fresh tree wounds. Pruning oaks during the growing season greatly increases the chances of insects infecting them with oak wilt.

What else can I do to protect my oak trees?

  • Prune oaks between October and February, not during the growing season.
  • Follow existing regulations and quarantines meant to protect our trees and forests.
  • Don’t move firewood. Firewood can transport oak wilt and other deadly pests and diseases to new areas.
  • Learn to identify the symptoms of oak wilt, which include discoloration around the entire leaf edge and sudden loss of a substantial portion of leaves during the summer.

For questions, contact the DEC Forest Health office at 1-866-640-0652, or email photos of tree symptoms to foresthealth@dec.ny.gov.

Visit the DEC website for more information on oak wilt.

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