Tree health concern updates for Maine

by Jessica Bern

Mike Parisio, forest entomologist with the Maine Forest Service, recently presented an emerald ash borer (EAB) regulation update from late 2021. The three takeaways were that he expects the boundaries of the emergency order area to remain the same, although that could change as summer marks the time when they do most of their monitoring; all out of state firewood continues to be banned from Maine, except certified heat-treated wood; and the Maine Forestry Service continues to rely on the public to inform them how the spread of EAB is proceeding in regulated areas (and, if they feel comfortable, reporting any instances of untreated firewood being brought over the border into Maine).

Project Canopy is Maine’s urban and community forestry program. According to Jan Santerre, Project Canopy coordinator, their role is to assist “cities, towns, schools, nonprofits and educational institutions with technical assistance as well as provide grants to help guide the management of urban and community tree and forest resources.”

Santerre’s said Project Canopy is always looking to the public to volunteer to help them monitor the spread of EAB and to help educate the public about what EAB is and its effects on trees.

She also offered some advice on managing your inventory. “The single most important thing you can do is to keep an inventory of your trees as well as your community assets,” she said. “In addition, you need to ask yourself what your staffing capacity is, take a look at who the consulting arborists are within your area and pesticide applicators,” to name a few. She added that you cannot manage anything if you don’t know what you already have. She suggested developing a timeline for management based on your inventory and asking whether or not you want to preserve ash trees, whether you’re going do any treatment, how infested wood would be dealt with, etc.

Tom Shmeelk, a forest entomologist, spoke about winter and browntail moths. According to Shmeelk, “caterpillars are hatching out and they’ll be feeding now through the end of May.” They create shot hole damage on maple and oak leaves, but they have other hosts, such as blueberries. Shmeelk said they’ve been using a parasitic fly, Cyzenis albicans, as a form of biological control to help reduce the winter moth population. It’s been a huge success, to the point where there were almost non-detectable traces of winter moth in some Northeastern areas.

He then spoke briefly about browntail moth and the closely related spongy moth (formerly known as the gypsy moth). The total number of acres defoliated by browntail moth in 2021 was 198,000, 45,000 more acres than in 2020. “It’s quite an order of magnitude worse than we’ve seen in the past few decades,” he said. The spongy moth “explosion” caused “55,000 acres of damage located primarily along the border of New Hampshire, with an additional 30,000-plus acres of defoliation spanning into the state [of Maine].” According to Shmeelk, cool, wet conditions seem to help to reduce both the moth population and the resulting damage.

Speaking about oak wilt and beech leaf disease was Aaron Bergdahl, forest pathologist for MFS. Beech leaf disease is new to Maine but has already had an impact on beech trees. The disease can kill both American and European species of beech and impacts Asian beech as well. As of today, according to Bergdahl, beech leaf disease is found in 109 U.S. counties, from Maine southward to Pennsylvania and westward to Ohio.

The symptoms of beech leaf disease are most easily seen by looking up at the tree canopy. Bergdahl said there are “very distinct dark bands in between the veins. It’s a fairly uniform pattern; not all leaves are impacted. A healthy American beech leaf looks papery thin … (but) when impacted with beech leaf disease, they are leathery, thicker, kind of rough, distorted and sometimes have raised banding.”

Tree health concern updates for Maine

The symptoms of beech leaf disease. Photo courtesy of Yonghao Li, CAES, Bugwood.org

Causes of beech leaf disease are unknown. Why the symptoms have developed so quickly and drastically in New England is another question for which they have no answer. According to Bergdahl, in Ohio it took over five years for the disease to move from killing the understory into the overstory. Yet, in Maine, Rhode Island and Connecticut, “It’s gone from zero symptoms one year to really advanced symptoms in the next,” he said.

Oak wilt is a complicated pathogen that’s very difficult to manage and lethal to oak trees. Thankfully, he noted, it’s not yet been detected in Maine. However, according to Bergdahl, it’s important to understand that it’s a lot like Dutch elm disease because it’s vascular, but unlike Dutch elm disease, it can kill a mature oak within in a month.

Also, like Dutch elm disease, oak wilt is spread by sap-eating beetles that are attracted to wounds on oak trees. “The beetles visit diseased oak, get covered with spores, then visit un-diseased wounded or freshly pruned oaks and spread the disease. The red oak is more quickly impacted while the white oak can persist for several years after infection,” he said.

Bergdahl warned that if you have an introduction of oak wilt via beetle, the tree will likely succumb in the first year. “Once a fungus gets into a vascular system it spreads quickly,” he said. The take home message is to not prune oaks during the growing season (May to September). “If you have to make a pruning cut, seal your wounds with latex paint or an actual commercial wound sealer for pruning trees,” Bergdahl said. He warned that oak wilt can also be spread through the movement of firewood from one area to another.

The final presenter was John Petrosky, manager of the Maine Pesticide Programs at the Maine Board of Pesticide Control. Through the board, you can find out what pesticides are registered in the state, their rules and regulations, about how pesticides can be applied and recommendations of people and companies you can hire to apply them as well as standards for water quality protection and what kind of management options and protection equipment you should use.

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