Pesticide application will limit use of Portland’s Deering Oaks

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Despite calls from some members of the public to use less damaging methods, Portland officials are planning to spray pesticides in Deering Oaks Park to eliminate what they say could be millions of destructive browntail moths.

Parks Director Alex Marshall informed the City Council last week the two biggest concerns driving the decision are overall tree health in the park and the public nuisance that browntail moths create in their caterpillar stage.

Browntail moth caterpillars on a tree. (Courtesy Maine CDC)

The caterpillars are covered in hair that can give some people a rash similar to poison ivy, and can also create respiratory problems. Parks and Recreation Director Ethan Hipple and Jeff Tarling, the city arborist, also said the caterpillars can be harmful to park trees, many of which are more than 200 years old.

“Deering Oaks is the (browntail moth) epicenter in greater Portland,” Tarling said.

The city surveyed more than 300 trees in the park, and Marshall said the city found more than 20,000 webs. Each web can yield up to 400 caterpillars.

The officials said the city has previously prioritized manually removing the webs, but Hipple said this year the numbers have spiked. One year isn’t catastrophic, he said, but the city is now entering the third straight year of high numbers of the webs. Marshall said many of the trees in Deering Oaks are also too tall to use a crane to manually remove webs, and there are just too many to get to.

Spraying a pesticide is the best approach the officials said, although they have not decided which one to use. They also described organic pesticide as a “wolf in sheep’s clothing,” since a pesticide is a pesticide.

The park will have to be closed for several days when the spraying begins in May, and for six weeks after the application changes in park programming will be necessary. The farmers’ market usually held in the park, for example, will be shifted to Payson Park until late June or early July.