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OAK WILT
oak leafs with oak wilt.Oak wilt is a disease that affects oak trees. It is caused by Bretziella fagacearum, a fungus that develops in the xylem, the water carrying cells of trees. All oaks are susceptible to the fungus, but the red oak group (with pointed leaf tips) often die much faster than white oaks (rounded leaf tips).

Threat to Oaks

The oak wilt fungus blocks the flow of water and nutrients from the roots to the crown, causing the leaves to wilt and fall off, usually killing the tree. Red oaks (scarlet oak, pin oak, black oak, etc.) can die within a few weeks to six months, and the disease spreads quickly from tree to tree. White oaks (bur oak, chestnut oak, etc.), often take years to die and the disease usually cannot spread to additional trees.

Origin of Oak Wilt

Oak wilt was first discovered in Wisconsin in 1944, but where it originated is still unknown. It has spread throughout the Midwest and Texas and has killed tens of thousands of trees in the U.S.

How Oak Wilt Spread

There are two main ways oak wilt is spread:

1) above ground by beetles

Fungal spore mats form just under the bark of infected red oaks after they have died from the disease. During the warmer months, these spore mats emit a sweet odor that attracts sap-feeding beetles and bark beetles, which can pick up fungal spores as they crawl around. The beetles are also highly attracted to fresh wounds in other trees-often caused by pruning. In this way, they spread the fungus from infected trees to healthy trees sometimes miles away. Infected firewood and other wood materials also pose a threat because they can harbor the fungus and/or beetles that can spread the disease.

2) below ground through tree roots.

Spread underground occurs when roots of nearby red oaks graft to each other (fuse together), creating a connection through which nutrients and the disease can move. In the Midwest, large blocks of red oak forests have died from the disease in a single season due to their vast network of interconnected roots. In contrast, white oaks are much less likely to create root grafts, and spore mats rarely form under their bark, significantly reducing the chance of spread from these trees.

Disease Symptoms

Symptomatic leaves from an oak wilt infected tree.

Symptoms of oak wilt infection are often very noticeable in red oak species, but aren't easily seen in white oaks.

  • Brown coloration develops on leaves starting at the outer edge and progressing inward toward the mid-vein of the leaf.
  • Branch dieback starts at the top of the tree's canopy and progresses downward.
  • Leaves suddenly wilt in the spring and summer and individuals may fall from the tree, typically while there is still some green on them. Most infected trees will lose over half of their leaves.
  • Fungal spore mats may develop under the bark of infected trees after the tree dies.

New York State Locations

Oak wilt has been found in four locations in Glenville, Schenectady County. Oak wilt was first was confirmed here in 2008, but resurfaced after treatment in 2013. Two new locations were found in 2017, and one new location was found in 2018. In 2016 oak wilt was then discovered in Islip, Riverhead, and Southold in Suffolk County; Brooklyn in Kings County; and Canandaigua in Ontario County. In 2018 and 2019, oak wilt was found in South Bristol in Ontario County and Middlesex in Yates County, respectively.

How Can You Help

  • Learn to recognize the symptoms of oak wilt including leaf discoloration, branch dieback, and fungal spore mats.
  • 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 water-based spray paint or 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 at www.dec.ny.gov/lands/46919.html

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