Watch out for oak wilt in July, August

oak leaves showing symptoms of oak wilt
Leaves from a tree infected with oak wilt disease may brown from the outside of the leaf toward the stem. Photo courtesy New York State Department of Environmental Conservation

The good news is that oak wilt, a serious disease for oak trees, hasn’t been spotted in Western New York yet. The bad news is that it has been identified in Ontario County, southeast of Rochester, as well as in other parts of New York State. See a map here.

The good news is that if oak wilt is found, steps can be taken to keep it from spreading.

July and August is the time to spot oak wilt disease, according to the New York State Department of Environmental Conservation (DEC). Oaks infected with the disease often stand out among healthy, green-leafed trees.

Oak wilt symptoms

Oak wilt symptoms include:

  • Leaves browning from the outer edge back towards the stem
  • Dieback starting in the top of the tree and progressing downward
  • Leaves of all colors will fall off, and many will still have green on them
  • Most or all leaves fall off in July and August.

In red oak species, symptoms can appear and progress quickly, sometimes leading to the death of the tree in as little as four to six weeks. White oak species typically die back just one or two branches at a time and may take years to succumb to the disease.

See more on oak wilt here.

Report oak wilt

If you suspect you’ve seen oak wilt, you can e-mail pictures of the tree (leaves, trunk, entire tree) and location information to foresthealth@dec.ny.gov. You can also call 1-866-640-0652.

Other ways you can help

Don’t prune oaks in spring or summer

Avoid pruning or wounding oak trees in the spring and summer, when spore mats are present and beetles are the most active. If an oak wound occurs during spring or summer, it should be sealed immediately with wound dressing. This will slow wound recovery but also deter beetles from landing on those areas, which will reduce the risk of oak wilt spreading. Learn more about the benefits of pruning oaks in the dormant season.

Avoid moving wood

To help prevent the spread of oak wilt disease, quarantine districts (areas where oak wilt has been identified) have been established in the towns of South Bristol, Canandaigua and Glenville; the borough of Brooklyn, and all of Suffolk County.

You can’t take oak logs or branches out of the quarantine districts. Also prohibited from leaving the quarantine districts are wood pieces less than 29 inches long, no matter the species.

In other areas, don’t move firewood from any tree more than 50 miles from its source. That rule is in place to help prevent the movement of several kinds of forest pests.

Some invasive pests of concern and their respective hosts are:

  • Asian loghorned beetle – maple, birch, ash, sycamore, poplar, willow, elm, hackberry, mountain ash, horsechestnut
  • Emerald ash borer – all ash species (white, black, green)
  • Asian gypsy moth – over 500 hosts including oak, basswood, birch, poplar, alder, willow, larch, hemlock, pine, and spruce
  • Light brown apple moth – apple, oak, pine, poplar, walnut
  • Brown spruce longhorned beetle – spruce
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