Methods of control can be categorized into biological (using natural predators and diseases), mechanical means (digging, pulling, cutting, mowing), and chemical means (pesticide use). Biological control, often called Integrated Pest Management is the utilization of a combination of methods in order to best manage species, while using the least amount of pesticide necessary. It is beyond the scope of this page. We will provide information on mechanical and chemical control, as these are the methods most used by individuals on their own properties.

General Guidelines and Considerations

  • Start on the outskirts of the infestation, and move towards the epicenter
  • Examine your expectation: The goal is to manage the population. Don’t expect to eradicate an entire species forever. Once a population is under control, however, management is much easier.
  • Return to sites repeatedly after a removal effort, to remove new seedlings, and re-treat new growth. Seeds may remain viable in the soil for years.
  • Never use hay in landscaping and gardening, only straw.
  • Be conscious of any landscaping materials you bring onto your property, as they may contain invasive seeds.
  • Be cautious when disposing of invasive plants and brush. Please see our information above on disposal.

Mechanical Control
Mechanical control is anything done to physically remove or kill a plant, such as cutting, pulling, and digging. It can be the most time-consuming and labor intensive. Mechanical control is not always practical or effective, depending on the species and size of the infestation. It is best to remove and cut back plants before they form seeds. If the plants have gone to seed, leave thems where they are to avoid spreading them further.

See https://extension.unh.edu/resource/mechanical-cont... for more information

Methods:

  • Hand pulling: Wear gloves. Some plants can cause skin irritation, such as bittersweet roots, and plants in the wild parsnip family. If root is left in the soil, a plant may regrow.
  • Digging: Some plants will require digging to remove an entire root.
  • Girdling: Cutting ¼-½” deep all the way around the trunk of large trees or shrubs to kill the plant above the cutting
  • Smothering: covering a plant with thick tarp or other material that will prevent sunlight from reaching a plant.
  • Cutting: effective at limiting seed-production. Some plants can be killed this way with multiple cuttings. Cut late spring, fall, and the following spring for best results.
  • Mowing: This can be used to prevent seed production. Clean equipment after use.

Chemical Control
Pesticides can be helpful in managing invasives. They can even be necessary at time. They should be used in combination with other methods, not depended on exclusively.

There are important details to consider before using herbicides. UNH Extension lists these four starting points:

  1. Understand the characteristics of the target invasive plant(s).
  2. Determine the level and size of the infestation.
  3. Develop a strategy for managing the infestation over time, based on landowner goals.
  4. Understand when a licensed applicator and permits may be needed to accomplish goals.


Safe use of Pesticides
There are many best practices for chemical application. You'll have to consider the:

  • The plant itself
  • The herbicide in use
  • Time of year
  • Weather
  • The surrounding environment

UNH provides detailed information at: https://extension.unh.edu/resource/chemical-contro...

Tips for Chemical Control
We cannot emphasize enough the need to read the entire bottle before using an herbicide. Not following the label is illegal and dangerous, and can cause significant environmental damage.

  • Be extremely cautious near wetlands and vernal pools. Certain herbicides can be extremely toxic to wetland animals in very small amounts.
  • Avoid using herbicides on a windy day, especially spray-application herbicides. Herbicides are extremely volatile, meaning they quickly evaporate into the air, causing drift to areas you don’t intend to treat.

Some people use a dedicated paint brush or similar to apply herbicide to stumps and stem ends. We’ve also seen people dip the ends of vines into herbicide.

Add food coloring to your herbicide so you can see both where you’ve applied, and anywhere the herbicide drips.
Spray at night, or avoid spraying while target plant and nearby plants are flowering, to protect pollinators.
https://extension.unh.edu/resource/chemical-contro...

FAQ

  • I have concerns about the effect of pesticides on humans and animals. Where can I learn more?
    • If you have concerns about a specific pesticides, the EPA publishes fact sheets on every pesticide here, including regulatory history. Please remember that EPA assessments of safety are based on following the label. https://www.epa.gov/ingredients-used-pesticide-pro...
  • What are laws surrounding pesticide use?
    • Only use on your OWN property
    • NO USE within 50 feet of a public water source, such as a pond, creek, lake, wetland.
    • “Beyond 50 feet from the reference line of public waters, pesticides can be applied as necessary and according to manufacture guidelines. Within 50 feet of the reference line, pesticides can only be applied by horticultural professionals who have a pesticide application license issued by the New Hampshire Department of Agriculture.” https://www.des.nh.gov/sites/g/files/ehbemt341/fil...
  • I’ve heard of using vinegar as an organic herbicide. Does this really work?
    • Vinegar will destroy the foliage of a plant, but the roots will remain unharmed. It may work on small, leafy weeds, with unestablished roots, but not on larger plants or plants with more established roots. Vinegar can also increase acidity of the soil, harming both plants and organisms.

Management Techniques for Types of Plants


Vines
Vines are one of those plants that generally require long-term management, instead of eradication. The fruit of some, such as Oriental Bittersweet, is eaten by birds, and then pooped out in new places. Your job will be to prevent vines from strangling other plants, and from creating large mats. Vines may be easy to pull from the ground in places where people don’t walk much, but requires digging in compacted areas. Herbicide may assist.

Small/thin:
Pull when able, digging to remove entire root system.
Repeated, weekly mowing can slowly deplete the root system, eventually killing the vines. This will not work if your mower cannot get low enough to cut the vine to the ground. If you are inconsistent with mowing, the vine will replenish its root system. This may take a number of years of mowing. https://www.aces.edu/blog/topics/forestry-wildlife...
Large/thick: Cut near ground, can apply herbicide to stump.
Manage vines in spring and summer, before seeds and fruit have ripened.

Non-woody Plants
Pull early in the year, before seeds have grown. Be sure to remove the entire root, especially with taproots (thick, single-stalk roots like carrots and dandelions).

Bushes, trees and Shrubs
Seedlings: Pull. Leave roots exposed to dry.
Saplings and trunks up to 2”: Use a weed wrench (the uprooter, pullerbear, etc) to pull entire plant out of ground
Saplings and larger trunks: Cut plant near to ground. Return and trim new growth periodically, or apply herbicide to cut sections (may require reapplication for a year or two).
Large: Use girdling technique for large trees
Fruiting/Seeding: Do not remove the plant from its site once fruit/seeds are ripe. You may use the above techniques, but leave the brush on-site.
For more comprehensive management, visit https://www.agriculture.nh.gov/publications-forms/...

Japanese Knotweed***

  • Do not mow Japanese knotweed. Knotweed is an extremely virulent invasive and can regrow and spread very easily from even small chips that are scattered by mowing.
  • Do not under any circumstances put cuttings in compost, dump in the woods, or bring to town brush.

Cut the knotweed close to the ground in early June and spray with appropriate herbicide by September
Leave cuttings on an impermeable surface to dry out, then bag in trash bags, tie the bags securely, and place in SOLID WASTE at the transfer station, or in your Regular Trash if a company picks it up.
Smother small infestations by using heavy duty black plastic or heavy duty weed fabric. (area needs to be covered for 5 years), OR repeat cutting in late summer, and spray with a glyphosate-based herbicide. Repeat for 3-5 years, or as needed until infestation is completely eradicated.
See page 16: https://mm.nh.gov/files/uploads/dot/remote-docs/en...
https://www.agriculture.nh.gov/publications-forms/...

Multiflora Rose
New Hampshire DOA recommends pulling smaller seedlings, and digging out larger plants roots 6’ out and down.
Repeated mowing for at least two years
“Soil, foliar, thin-line, and basal bark application methods can be used to apply herbicides for multiflora rose control. To determine the most appropriate treatment method, carefully read the herbicide label.” https://extension.psu.edu/multiflora-rose-manageme...