Second aerial spraying scheduled early Wednesday for Duluth, Cloquet neighborhoods

The Minnesota Department of Agriculture aims to stop the spread of leaf-eating spongy moths.

spongy moth caterpillar
The leaf-eating, caterpillar stage of the spongy moth. Agencies in eastern Minnesota and western Wisconsin this summer will use aircraft to spray against the insects, including in Duluth and Cloquet, to reduce damage to forest trees.
Contributed / Minnesota Department of Agriculture
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DULUTH — Residents of some Duluth and Cloquet neighborhoods may again be awakened by the sound of a low-flying airplane Wednesday morning when the Minnesota Department of Agriculture is planning to spray trees to eradicate spongy moths, the invasive pest formerly known as gypsy moths.

This is the second spraying after the first occurred last Wednesday.

The aerial treatments will start as early as 5 a.m. in western Duluth followed by Cloquet. It may take up to two hours to complete both areas.

The Duluth site is approximately 75 acres in the Gary-New Duluth neighborhood, from 98th Avenue West to the railroad tracks and extending from Bowser Street to near Minnesota Highway 39. The Cloquet site encompasses approximately 500 acres around the Sappi mill property, including the area near the St. Louis River and Cloquet Avenue.

The low-flying airplane will be traveling up to a half-mile outside these treatment areas as it navigates through the insect infestation sites spraying Btk, a biological control chemical.


Aerial spraying for spongy moth is planned in eastern Minnesota and western Wisconsin this summer.

Btk is a biological product that is organic-certified for food crops. The department says Btk has no known health effects for humans, pets, birds, fish, livestock, bees or other non-caterpillar insects, although some critics say it can harm butterfly caterpillars if they are at the same life stage as the moth caterpillars.

spongy moth
A spongy moth.
Contributed / Iowa Department of Agriculture and Land Stewardship

The Department of Agriculture has set up a Report a Pest Info Line at 888-545-MOTH with the latest details about treatment dates and times. The department’s website,, also has information about spongy moths and control efforts. Residents can sign up for updates about treatment progress by texting “MDA MOTH” to 468311 to receive text notifications or texting “MDA MOTH (your email address here)” to 468311 to receive email notifications.

The residue does not cause damage to outdoor surfaces. Soapy water will remove any residue.

Eastern Minnesota and western Wisconsin are the national front line in the battle against invasive spongy moths as they continue a century-long push west across North America. The leaf-eating caterpillar stage of the moth are among America's most destructive tree pests, having caused millions of dollars in damage to eastern forests. If present in large numbers, gypsy moth caterpillars can defoliate large sections of forest. Oak, poplar, birch and willow are among their preferred hosts.

The moths spread slowly on their own, but people can unintentionally help them spread by transporting firewood or other items on which the moths have laid their eggs.

John Myers reports on the outdoors, natural resources and the environment for the Duluth News Tribune. You can reach him at
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