Watch Out for Oak Wilt

Tree with oak wilt. Photo by NYS DEC staff.

In 2016 oak wilt was found at new locations in Islip, Riverhead, Southhold, Brooklyn and Canandaigua in addition to a known location in Glenville, New York. Since so many new locations surrounding our region were discovered last year, it is important that we are all aware of what the signs of this disease are and that any new locations are discovered quickly and reported.

Oak wilt (Ceratocysis fagacearum) is a fungus that infects the conductive tissue (water carrying cells) of oak trees.  The fungus blocks the flow of water and nutrients from the roots to the crown of the tree. Susceptibility depends on the species of oak.  Species in the red oak group may die within 1-5 weeks, while species in the white oak group may persist for years. In red oaks, fungal spores can be transported through all parts of the tree as the tree nears death; but in white oaks the distribution of spores only occur in the xylem of the current year’s growth.

Oak wilt was first discovered in Wisconsin in 1944 and has spread through the Midwest from Minnesota to Texas.  It was first found in New York State in 2008 at the Glenville site.  

Symptoms of oak wilt include browning of the leaves from the tip and edges moving in towards the midrib of the leaf.  Trees will shed leaves in late spring to early summer.  Infected red oaks lose their leaves from the top down, while in the white oak group leaves are lost in sections. 

Necrosis of the leaves from tips and margins. Photo by NYS DEC staff.

The fungus can spread naturally in two ways: above ground by beetles and below ground through root grafts. The fungus produces a fruity smelling mat of fungal spores under the bark of oak trees killed by the oak wilt fungus. These spore mats attract sap feeding beetles which can carry the spores from diseased trees to healthy trees. The sticky spores from these mats adhere to the insects’ bodies, and the beetles carry the spores to wounds on healthy trees. Oak wilt is also transmitted from tree to tree by underground connections called root grafts. Fine root grafts commonly occur between trees.

Humans can also spread the fungus over long distances by moving infected wood products or nursery stock.

If you observe an oak tree dropping leaves in early summer, and suspect that you are seeing symptoms of oak wilt, please take pictures of symptoms and report your sighting to DEC Forest Health or call 1-866-650-0652.  To learn more about oak wilt and Early Detection in our region, watch for upcoming CRISP events!