To our readers,

The COVID-19 pandemic is a once-in-a-century type story, ... Click here to continue

Invasive pests and plants continue to pose problems in Midcoast

By Gabriel Blodgett | Jul 23, 2019
Photo by: Gabriel Blodgett Japanese knotweed grows on Route 17 in Rockland.

Rockport — As we move past the worst of the 2019 brown-tail moth invasion, there are still myriad invasive pests and plants in our midst and on the horizon that require vigilant attention.

Hildy Ellis, program manager at Knox-Lincoln Soil & Water Conservation District, will be giving a free presentation on invasive forest pests at Merryspring Nature Center Saturday, July 27 from 10 a.m. to noon. The pests she will discuss include emerald ash borers, hemlock woolly adelgids, and Asian longhorned beetles.

One of the biggest potential threats to Maine forests is the emerald ash borer, which has been found in York and Aroostook counties. The Maine Department of Agriculture, Conservation and Forestry issued a quarantine on the insect and “material that may harbor it” April 17, which includes all species of ash found in the state. Recently, the Maine Forest Service released parasitoids, which are “tiny non-stinging wasps that feed in or on EAB by attacking immature (larvae) EAB under the bark of ash trees and parasitizing eggs on the surface of the bark,” according to a DACF press release.

Locally, posters have been attached to elm trees to increase awareness of the potential threat and remind people not to transport firewood.

Like many invasive insects, the size of the EAB – it fits easily on a penny – makes it difficult to spot, so the best way to identify its presence is to look for changes in the environment.

“Most discoveries of invasive expansion are by people who recognize signs of decline,” said Ellis.

For that reason, much of the work of conservation districts consists of education and outreach through events like the one at Merryspring and presentations and information booths at fairs and shows. She said they also speak at town offices and libraries, as well as providing training for government employees like highway workers, who spend a lot of time on roads and may be more likely to spot changes in the landscape that indicate the spread of invasive pests and plants.

A main difficulty, however, is reaching the people who do not attend workshops or go to fairs, and for that reason she said it is important to engage with neighbors and friends to help spread awareness.

Pests are not the only invaders threatening local habitats. The Maine Natural Areas Program of the DACF recently released an updated advisory list of invasive plants that now includes 124 species it recommends avoiding in gardens. This list expands on the state horticulture program’s 33 species list of plants that are illegal to sell, import or intentionally propagate.

Nancy Olmstead, who has worked for five years as an invasive plant biologist for the MNAP, said it is hard to determine whether invasive plants are spreading more quickly or people are becoming more aware of them, but “once [people] recognize them, they’re amazed at how widespread they are.”

She pointed to Japanese knotweed and glossy buckthorn as two plants having especially large impacts in the state. Knotweed, which looks like bamboo, grows from tiny rhizomes, allowing it to spread easily through rivers and waterways, where it “tends to infest areas that are difficult to treat.”

This includes the northern woods, where very few invasive species have taken hold.

She said that glossy buckthorn, which many people would confuse with young cherry or birch trees, has spread in diverse habitats because of its ability to flourish in both sun and shade. She said it has dense infestations along remote rivers and poses a threat to both forests and wetlands by out-competing native tree species.

With both invasive pests and plants, one of the major issues is that when they are introduced to a new environment, it is often devoid of diseases and predators that have kept them in check in their native habitat.

Control of invasive species generally requires a combination of cultural, mechanical and biological methods, but Ellis said that eradication is often not a reasonable goal.

“Certain plants and insects are here to stay.”

An example of cultural control is smothering with a tarp, while mechanical control is generally physical removal, and biological or chemical control is the use of pesticides or the introduction of a biological control agent like the parasitoid wasps for EAB or several species of beetles that were introduced to help stop the spread of purple loosestrife.

Management often requires a combination of the three, and while Ellis said it is often best to start with “the least toxic reasonable method,” sometimes chemicals are necessary and there are ways to “limit the exposure of chemicals to the environment.”

She cited the example of brushing chemicals on cut trunks of Norway maples as a method that is effective and does not have a particularly adverse impact on the environment.

Ellis suggested always monitoring the area first and rather than attacking the biggest problem section, prioritizing areas that are important and useful, and attacking from the outside in.

She also stressed the need for a plan after eradication, as uprooted soil is prone to the same species reasserting its position or even another invasive species taking advantage of the opening.

While Ellis said managing invasive species on your own property can be possible, provided you have the appropriate tools and time to dedicate, on larger plots of land and farms, dealing with invasive species can be much more of a burden.

According to Ellis, invasive species cost the United States billions of dollars every year in control efforts, not accounting for the loss of revenue for commercial farmers caused by these incursions.

In 2015, along with the Kennebec Soil and Water Conservation District, Knox-Lincoln SWCD received a Conservation Innovation Grant to help farmland and woodland producers identify, map and strategize ways to deal with invasive species. Ellis said the grant, which was spearheaded by MNAP, has been effective in keeping producers informed on what issues are facing other farms and forests throughout the state and sharing successful management practices. Participation can also help farms get future grants to help offset losses in revenue caused by invasive species by showing that the owner has already made an effort to deal with the issue. Ellis said the grant is continuing, showing that the state, and the Midcoast in particular, is on the cutting edge of the invasives movement.

There are also a number of secondary consequences that invasive plants have on the environment that cannot be easily measured. Ellis said the fruits of many invasive species are not as nutritious as native plants, and are often higher in carbohydrates and lower in lipids. The fruits generally grow during the time of migrations, making it more difficult for birds who require lasting energy to complete their journeys.

Monarch butterflies can only grow on milkweed, and while Ellis said not all butterflies are as host-specific, they all evolved with native plants, which are pushed out by invasive species.

Overall, she said, native wildlife requires at least 70 percent native plants to get enough food.

Ellis said there is an increasing number of ways for people to engage with the fight against the spread of invasive plants.

Recently MNAP released a Maine Invasive Plants Field Guide that is waterproof and in full color for $18. Discoveries can be logged on a relatively new website,, that lets people to mark invasive species on a map, allowing the department and the public track their spread.

Ellis said there is also a plant identification app called PlantSnap that can help people determine whether they are looking at an invasive species.

There is also the matter of making sure that your own property contains a majority of native plants.

“We have total control over what we grow in our yards,” said Ellis.

Anyone wishing to attend the invasive forest pests workshop should contact Knox-Lincoln SWCD to register.

If you appreciated reading this news story and want to support local journalism, consider subscribing today.
Call (207) 594-4401 or join online at
Donate directly to keeping quality journalism alive at
Comments (0)
If you wish to comment, please login.
Note: If you signed up using our new subscriber portal, your username is the email address you registered with and your password is in all caps