Deering Oaks will be temporarily closed to apply pesticides and the Portland Farmers Market will move to Payson Park for up to six weeks as the city battles an infestation of browntail moths.

Portland parks and recreation staff will present its plan for controlling the infestation during a City Council virtual workshop at 5 p.m. Wednesday.

The city’s Pesticide Ordinance contains an exemption that would allow pesticide use if public health and oak trees as old as two centuries are at risk, according to Ethan Hipple, director of the Parks, Recreation and Facilities Department. That means using pesticides in Deering Oaks will not require a waiver from the city, said Hipple.

“We are making the council aware of our plans,” Hipple said Tuesday evening.

Under the plan, published Tuesday on the city’s website, Portland will close the park for one or two days while infested trees and their canopies are sprayed during the first week of “budbreak,” or the week of May 20.

Hipple said the city also is moving large-scale events out of the park for six weeks because of the effects the caterpillar hairs can have on the public, such as causing itchy rashes or respiratory problems. Except for the temporary closure to apply pesticides, the park would remain open.


Hipple said the city has been talking with representatives of the Farmer’s Market about relocating to Payson Park. City staff recommend it be relocated from May 17 to July 2. City staff have also been working with representatives of Wednesday’s farmers market, which typically operates out of Monument Square, but was moved to Deering Oaks last year because of COVID spacing concerns, and might do so again.

A browntail moth caterpillar Maine CDC photo

The city’s top priority during spraying will be to protect public health as well as the health of the 1,000 trees in Deering Oaks, Hipple said. Many of the trees are heritage white oak trees with historical value, and he estimated there are dozens of trees in the park that are up to 235 years old. Browntail moths defoliate trees and, if left unchecked, can kill them.

“That means they were seedlings around 1785 which puts in perspective how precious these trees are,” Hipple said.

A survey by the city and the Maine Forest Service, completed in January, showed that 313 of 316 trees had browntail moth nests. Three heritage oak trees had more than 1,000 nests each and two others had 500 to 1,000 nests. Hundreds of nests were found on dozens of other oak trees.

In his report to the City Council, which was posted Tuesday on the city’s website, parks Director Alex Marshall said drought conditions in 2020 accelerated the browntail infestation. A soil-based fungus controls the moth population, but the lack of moisture curbed fungus growth and opened the door for the population boom.

“Over the past few years, staff have attempted to manage the browntail moth population by clipping nests and injecting infected trees with a pesticide. However, due to the 2020 drought the population grew to a size where those techniques are no longer effective,” Marshall said in his report. “Their impact on the health of the Parks’ trees, and the Park itself, is increasingly negative and problematic. The defoliation caused by browntail moths can lead to branch dieback within just a couple years. This will lead to the death of many of the Parks’ trees, including its heritage oaks, over the next few years unless we intervene now.”


The moths also pose a public health threat because they have tiny, poisonous hairs that can cause a dermatitis reaction similar to poison ivy on sensitive individuals. The hairs also can cause breathing problems if they are inhaled. Reactions in humans can last for a few hours up to several days.

“I wouldn’t call this a public health crisis and no we’re not going to close the park to the public, but visitors to the park will see signs posted warning them about the browntail moths,” Hipple said. “Now, we need to be more assertive in addressing this problem.”

It is not clear whether Portland Protectors, a grassroots organization that advocates reducing the use of pesticides, will object to the use of pesticides in one of the city’s most heavily used parks. A spokesperson for the group could not be reached Tuesday.

Portland Protectors helped convince the city to adopt an ordinance in 2018 regulating pesticide use. Since July 1, 2019, residents and city workers cannot freely use synthetic pesticides in Maine’s largest city, except in a few limited cases.

Note: This story was updated Feb. 10 to clarify that large-scale events will be moved because of the risk of people being exposed to the caterpillar hairs and not because of the pesticide application.

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