HOULTON, Maine — Although autumn is right around the corner, a number of maple trees in the Shiretown have already started to, and in some cases completely lost their leaves, leaving many to ponder what is the cause.
Jane Torres, the executive director for the Greater Houlton Chamber of Commerce, said she first noticed a couple of weeks ago that some of the town’s large maple trees had bypassed the changing of colors from green to yellow and red and went straight to brown before falling to the ground.
“For those of you who have maple trees in your yard you may have noticed that many of them are losing their leaves in a rather alarming fashion,” Torres said. “On my nightly walks around town I have noticed this predominantly on the Norway maples, but some of the royal reds are being hit too.”
Torres contacted Dan Jacobs, a member of the Maine Forest Service who resides in Littleton, who is the town’s go-to person for all things tree-related. According to Jacobs the trees have a fungus-type disease commonly known as “Tar Leaf Spot.”
“I have looked at a number of the trees and it appears they are affected with Tar Leaf Spot,” he said. “The species I found it in primarily is the Norway maple, however it can be in other species of maples as well.”
According to the Maine Forest Service’s website, Tar Leaf Spot, can be caused by several different types of fungi. “The three fungi affecting maple are in the genus rhytisma. All species of maples in Maine can be affected by tar spot, but the particular pathogen that is most damaging to Norway maples is rhytisma acerinum. The tar spots that can occur on sugar maple, red maple, and our other native maple species is caused by one of two other species of rhytisma (R. americanum and R. punctatum). Tar leaf spot diseases that occur on our native maple species are occasionally observed, but cause inconsequential damage.”
Determining which trees are affected is tough to pinpoint.
“Early in the growing season it is difficult to see it,” Jacobs said. “Later in the growing season, you see these black spots on the leaves. If there are multiple infections in one leaf, it will turn brown and fall off.”
Jacobs said he classified the level of infection in Houlton as “moderate,” but there were some individual properties that fell into the “severe” category. Trees along Court Street and Pierce Park, which is where the town’s “Boy and the Boot” statue is located, are among the hardest hit areas, Jacobs said.
“It’s actually good that the defoliation happened this late in the growing season,” he said. “The leaves have basically already done their job. So most likely the trees will be fine next year.”
The disease has little detrimental effect on the long-term health of the affected trees. Infected leaves retain most of their photosynthetic capabilities throughout most of the growing season, according to Jacobs. The buds for growth next year have already been set. Leaf drop is late enough in the season so that a refoliation by the tree is not triggered. This means that the energy reserves already stored will be sufficient to allow the tree to develop normally next spring.
The only way to treat the disease is through a fungicide application, Jacobs added.
“That application would have to be done very early in the growing season, in May or early June,” he said. “That also has to be done by someone who is licensed. I don’t recommend any homeowner to do this on their own.”
Chances are high that an infected tree will have a similar problem next year, as the fungus will survive throughout the winter and return next spring. He suggested visiting the Pesticide Licensing Board on the www.maine.gov website to find a list of those individuals certified to treat trees. Consulting a licensed arborist is another option.
Jacobs added it was important not to leave the diseased leaves on the ground or in compost piles as which will allow the fungus to grow.
“The have to get rid of the leaves,” he said. “Whether that be by burning or hauling (the leaves) away is the best way.”
