Now through February is time to prune oaks to protect against disease

oak leaf with wilt
Oak leaf with wilt. Photo courtesy New York State Department of Environmental Conservation

Pruning oak trees now through the end of February 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 is caused by the oak wilt fungus. One way oak wilt spreads is by the fungal spores hitching rides on insects. Sap beetles, one of the main culprits, are extremely attracted to fresh tree wounds. If you prune when the insects aren’t active, it decreases the chances of the disease spreading.

That’s why you should prune oaks between October and February, not during the growing season when insects are active.

Oak wilt has been found in other parts of New York State. 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.

The oak wilt fungus clogs the trees’ transport vessels, cutting off water and food from leaves and the rest of the tree.

Besides helping to prevent disease, other reasons for pruning trees in fall or winter are:

  • 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.
  • Trees pruned in winter respond more vigorously in the spring, putting out new growth.
  • Removing weak and damaged branches before heavy snowfall reduces additional breakage.

Another thing that helps to prevent the spread of tree diseases is refraining from moving firewood. Firewood can transport oak wilt and other deadly pests and diseases to new areas.

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

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