Pesticide Use in the Wildlands

Pesticide Use in the Wildlands

September 2019

Colored text is links to other resources. 

Note: Pesticide is the general term for substances that kill undesirable things; herbicide refers to plants, insecticide to insects

GPMCT’s goal in the Wildlands is to protect and manage the property for wildlife habitat, sustainable forestry and public recreation. Sometimes, to fulfill that mandate, the considered and judicious use of pesticides is justified and sometimes essential. 

History of Wildlands Management

Although the Wildlands was initially relatively pristine forest, 20 years ago it was largely clear cut which dramatically altered ecosystems, encouraged many non-native species, and caused major erosion problems. Since then, to protect the streams, ponds and wetlands, the Trust has spent hundreds of thousands of dollars to rebuild and improve the roads, bridges, culverts and trails in order to control erosion and recreate the natural passageways of aquatic organisms. 

We have spent similar amounts, with the guidance of several highly-regarded foresters, to rebuild the forest, not only to bring back the magnificent Northern Forest that was once thriving there, but also to rebuild the habitat to encourage the return of native wildlife. So far, we have been very successful. Because of the earlier human interventions, as well as some of our early construction projects, several species of invasives (aggressive imported plants that have few natural enemies, like barberry, autumn olive, japanese knotweed, and others, that crowd out native species) are present. However, given the size of  the property and the environmental indignities visited on it, the Wildlands are remarkably free from major invasive problems. We have worked to keep it that way for fifteen years. 

Reasons for Current Pesticide Use

It is in this current context of rebuilding the forest and controlling invasives that we use pesticides- in this case herbicides. We have been using them since 2006 in very specific locations and situations. Although we can envision a time when we may need to also use insecticides to protect trees from invasives like the emerald ash borer and wooly adelgid infestations that are killing centuries old ash and hemlock trees in other parts of New England, we do not currently. Occasionally we apply herbicide to poison ivy when it is in an area where people are working (usually in forestry management) or where many people, especially children and dogs, congregate.

We are not advocates of pesticides. Where there are appropriate alternatives, we use them. But in some cases, the safest, least environmentally damaging solution, is pesticides.  We are not alone. Almost all large conservation landowners, including land trusts, reluctantly use pesticides. Most land trusts in Maine, at least occasionally, use pesticides. The National Audubon Society, the Trust for Public Land, The Nature Conservancy (TNC), the State and National Forest Services, and the State and National Park systems all use pesticides. Most of these organizations, including GPMCT, use alternatives where they are effective and efficient. We use pesticides to manage forests and invasive species because the alternative is much worse. 

This article discusses the trade-offs land managers make and how herbicides are a small but essential part of their work battling invasives. It’s not written by a pesticide industry apologist, but by The Nature Conservancy (TNC), a global environmental nonprofit that employs more than 400 scientists in 72 countries across six continents.

Allowing invasives a foothold can cause major changes in the ecosystem. In the case of autumn olive, which we have in the Wildlands, it out-competes and displaces native plants by creating a dense shade that hinders the growth of plants that need lots of sun. It can produce up to 200,000 seeds each year, and can spread over a variety of habitats as its nitrogen-fixing root nodules allows the plant to grow in even the most unfavorable soils. Birds scatter the seeds along roadsides and forest edges, often completely taking over log yarding areas.

Japanese knotweed (often called bamboo), another invasive present in the Wildlands, is extremely aggressive and very difficult to eradicate. It has completely colonized the entire corridor of hundreds of streams in New England. Once in the water course, it establishes itself quickly and kills off all other stream/river bank vegetation. This eliminates the native species that insects feed on, and in turn reduces or eliminates fish populations. Stream and river banks colonized by knotweed are much more susceptible to erosion, which in turn compromises the water quality and ecosystem. Knotweed reproduces easily from small pieces of stems or roots, as well as from seed. The current pattern of knotweed infestation is best managed by application of herbicide on individual plants.

In managing the Wildlands forests, one of the main challenges is the invasive beech bark scale insect and its accompanying fungus that decimate the American beech. These diseased beech are significantly altering the whole forest by reproducing so rapidly that they crowd out other species. Without intervention, parts of the Wildlands will evolve into stands dominated by diseased beech. Pesticides are one tool among many we use and we continue to experiment with alternative management techniques.

Current Specific Uses of of Pesticides

We have generally used guidelines published by TNC. They recommend science-based practices for managing invasives, including the use of pesticides when there isn’t another viable solution. 

In the past we have hired a contractor to treat phragmites (a wetland  invasive reed) with herbicides. It is currently under control and we are monitoring it.

Pesticides were used on Russian Olive in 2012 & 13, combined with several mowings; it was successfully eradicated. We have also used pesticides on autumn olive, and while it has not been eradicated entirely, it is tentatively under control. . This summer we have used mechanical methods (digging, cutting) to remove it, but cutting can cause spreading as the shrub germinates easily. We are monitoring it at present, but expect some of the larger roots may require herbicide. 

We have successfully eliminated several patches of knotweed in the past with herbicide. We are currently using herbicide on 2 single plants and 1 small area about 10 feet square, all of them in or next to water courses where mechanical disturbance is likely to send plant material that can regenerate downstream. Their location is of special concern because of knotweed’s predilection to take over water courses very quickly. Although the patch, which is near the bank of Hot Hole stream, was treated experimentally with salt and vinegar and covering with a tarp, we  concluded that salt that close to the stream may be toxic to fish. 

For forestry purposes, we have treated stands of small, diseased Beech with herbicide manually applied to a small section of bark. We have also treated freshly-cut stumps of beech to prevent root-sprouting and further proliferation of diseased trees. Last year we also experimented with “high-stump” cutting. We think it may be a reasonable alternative to pesticide treatment, but has its own environmental impact. It requires running 2-stroke chainsaws with high levels of exhaust and oil emissions for hours at a time.

The Maine Natural Areas program publishes excellent resources for managing invasives. It lists Japanese knotweed as severely invasive and recommends:

New patches (<20 stems) can be cut repeatedly throughout the growing season*, as often as once/week, for several years. Larger patches cannot be controlled manually without a persistent, reliable labor source. Smothering with heavy black landscaping cloth or erosion control fabric can be successful but requires biweekly maintenance and must be repeated for up to 10 years; see references for sources of information on this method. Herbicides† are effective. For small patches, use stem injection or cut-drip applications of glyphosate*. Be sure to dispose of cut stems carefully. For large patches, cut or mow when plants are approximately 3′ tall, then apply glyphosate as foliar spray when plants have re-grown to 3-5′ tall later in the same growing season, or apply to uncut, mature stems just before flowering. Avoid application of foliar herbicide during flowering as bees are attracted to this species. Follow-up will be needed in almost all circumstances. 

Autumn olive is listed as very invasive and the recommendation is:

Small plants and seedlings may be pulled up by the roots when soil is moist; larger plants can be cut, but re-sprouting will occur*. Persistent cutting or burning of the the root crown multiple times during the growing season over several years may kill the plant, but diligence is required. Mowing can prevent seedlings from establishing. Goats and sheep will browse it but repeated, heavy damage over multiple years is required to kill established shrubs. Herbicides† are effective as foliar applications (glyphosate or triclopyr solution), cut-stump application (glyphosate or triclopyr solution applied immediately after cutting except in early spring), or basal bark application (triclopyr ester in bark oil). 

Alternatives to Pesticides

As noted above, we have frequently opted for alternatives to pesticides; some of them work, some don’t. An internet search will produce dozens of supposed alternatives, but many of them either don’t work in our particular situation or have more environmental impact than the pesticide they replace.

  • Vinegar : There are commercially available herbicides that use high (20%) concentrations of vinegar. They work on some plants, but  they are toxic to fish and aquatic invertebrates. They are also not effective on knotweed because they do not reach the root system.
  • Salt: same issues as vinegar and is toxic to many of the surrounding plants
  • Tarps: can be used with other methods to control knotweed and other invasives, but require smooth ground or addition of material to ensure a close-fitting cover. Generally takes several years to completely eradicate
  • Mowing: can be part of solution, but takes years to eliminate
  • Goats: a possible solution in some areas with large infestations; knotweed requires cutting down to the ground many times each season over a few years, so it’s impractical with very small patches. Also, farm animal droppings on stream banks are more damaging to the water quality than appropriate application of pesticide

Types of Herbicides Currently in Use


The active ingredient in Roundup® and many other brands of herbicides. 

Glyphosate is the most widely used post-emergence herbicide for several reasons:

  • It is effective. Glyphosate is a systemic herbicide that moves from the treated foliage to other plant parts, including the roots. 
  • Glyphosate has little or no soil residual. It is rapidly bound by clay particles in the soil rendering it inactive. This means that glyphosate that comes in contact with the ground will not run off into water systems and becomes inactive. 
  • It is considered to be one of the least toxic and environmentally benign herbicides in use.
  • Spraying food crops directly with glyphosate, as opposed to spot-treating invasives, is another matter. As traces of glyphosate have started appearing in food, we need to understand the risks and encourage regulators and corporations to better assess, test and regulate pesticides.

GPMCT uses glyphosate as a spot treatment on specific invasive plants. We do not “spray,” but drip a solution of 2% Roundup® directly onto the leaves of each plant. We do not use Roundup® on invasives on the banks of streams, or in the water (where phragmites, an invasive wetland reed grows),  because the “inert” ingredient in Roundup®, a surfactant, can be toxic to aquatic life. Other formulations of glyphosate are safer in water. We also know glyphosate may be harmful to bees. Treating invasives before or after they flower eliminates this possibility.

For more information on glyphosate, see the National Pesticide Information Center website.


The active ingredient in Garlon, Renovate, Pathfinder and many other brands of herbicide. Triclopyr is often used to treat urasian milfoil in lakes. It is a relatively safe herbicide when used appropriately. We have spot-sprayed it on phragmites, as well as on freshly-cut stumps of diseased beech. We anticipate using it on autumn olive where mechanical removal hasn’t been effective.

For more information on glyphosate, see the  National Pesticide Information Center website.

The Future

The use of herbicides and management of invasives is evolving and GPMCT will likely change its practices as other herbicides and herbicide alternatives are developed, and as other threats emerge, such as Hemlock Wooly Adelgid and Emerald Ash Borer. 

We are currently developing a pesticide policy that reflects our current use and directs our future use of pesticides. It will require us to do more documentation of the specific areas, pesticides and purposes for the applications, as well as documented  follow-up. We will also notify Wildlands users if pesticides are used on roads or trails or other places people are likely to be present.

It is likely we will also evolve to using only State-certified Pesticide Applicators, instead of willing volunteers. We have never asked staff to apply pesticides against their wishes. As in the past, we will rely on the long experience of our licensed professional forester for advice, and continue to research and apply best practices.