All Eyes Are on the Oak Trees

Keep a watch on your oak trees this summer. By season’s end, it will likely be obvious if any have been struck by oak wilt disease, a fungus that is readily spread and easily kills the trees.

Infected oaks must be taken out and the wood properly disposed of. Pruning can spread the disease by exposing oak-wilt spore, which attracts beetles that carry it to other trees, so it should be left until the fall.

Earlier this year, after several infected trees were found in Southold and Wading River, as well as upstate, the State Department of Environmental Conservation issued a ban affecting all of Suffolk County, prohibiting the moving of oak branches, logs, stumps, or any kind of firewood less than 29 inches long, either in or out of the county. A total of 15 infected trees were found and removed last year.

The D.E.C. will conduct aerial surveys over the East End this month and in September, and take samples to look for infected trees. Residents have been asked to monitor their properties and report possible infection.

There is “one property unique to this disease, the tendency to drop leaves in the middle of the summer,” Margery Daughtrey, a plant pathologist at Cornell University’s research and extension service in Riverhead, said this week.

At other times of year, she said, particularly in spring, squirrels might be the culprits if oak leaves are found scattered on the lawn and tooth marks are found on branches. This past spring was cool and rainy, which could have delayed the onset of symptoms in infected trees, Ms. Daughtrey said, so residents should be especially watchful now.

Leaf loss and browning leaves are “key symptoms” of oak wilt. “The other clue is sudden death of an oak,” Ms. Daughtrey said. “The only other thing that does a quick kill is a lightning strike.”

“Dying from the top down,” she said, “is characteristic of this disease.” Red oaks in particular may quickly succumb.

Dieback generally starts at the top of the tree’s canopy and moves down, with brown coloration on leaves starting at their outer edge and progressing inward. Leaves suddenly wilt, and may fall when green or brown. Fungal spore mats may develop under the bark, causing it to raise and split.

When reporting a suspected case of oak wilt to the D.E.C., homeowners should provide good photographs of the whole tree, as well as close-up pictures of the leaves. If there has been a recent lightning storm nearby they are asked to note it.

An infected tree must go, said Ms. Daughtrey, “because it represents a danger to the other trees in the area.” The D.E.C. has worked with homeowners to make arrangements for tree removal and disposal.

People who see oak trees that are suddenly bare of all or most of their leaves this month or next have been asked to call the D.E.C.’s forest health information line at 1-866-640-0652, or send an email to [email protected].  Photographs of the damage are encouraged.

“I think we’ll have a better handle on this by the end of the growing season,” Ms. Daughtrey said.