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March 2012

Types of Weed Control

Contact: Tim Culbreth, Maryland Department of Natural Resources
TCulbreth@dnr.state.md.us

ANNAPOLIS, MD (March 20, 2012) - For March, the Maryland Invasive Species Council Invader of the Month is taking a different approach and wants to educate everyone on the methods of control available to use in the war on terrestrial invasive plants. At the most basic level, invasive plant control can be broken into three categories: mechanical, chemical, and biological. Concerned landowners should be able to employ most of the tactics outlined in the following document to help improve the health of their land. The end of this IOTM includes many interesting tactics better employed by professionals.

The Maryland Home and Garden Information Center describes invasive plants as those species that threaten our native plants and animals. Some native plants face extinction. Native wildlife suffers because it evolved dependent on native plants for food and shelter. All invasive plants as well as invasive pathogens, diseases and animal, have one thing in common – mechanisms to colonize, out-compete, and exclude indigenous flora and fauna radically altering indigenous ecosystems and the services which they provide.

The best and easiest control is early identification and quick removal. Established plants can be eliminated, often easily, once good control methods are known. This publication highlights popular invasive plants that are known to be present and have negative characteristics in Maryland and the Mid-Atlantic region. The degree of invasiveness may vary by region.

Before any control methods are employed, please make sure Personal Protective Equipment (PPE) is worn and used properly. PPE for invasive plant removal includes goggles, long-sleeved shirt and pants, gloves (rubber for use with chemicals, leather for pulling brush), boots, and a respirator if conditions require it.

Integrated Pest Management (IPM) provides a framework for decisions about the control and management of invasive plants and animals. IPM is not a single species control method but, rather, a series of pest management evaluations, decisions and controls. Selection of an optimal invasive species control tactic to manage the problem while minimizing economic, health and environmental risks is very important. Questions that should be asked include:

  • Are there opportunities to integrate nonchemical tactics?
  • How well will the control option fit into the total management of the ecosystem?
  • How well will the tactic control the invasive species?
  • What effects will this action have on the user, society as a whole, and the environment?
  • Will this action impact, either positively or negatively, the other insect pest species, indigenous flora or fauna or natural enemies of the invasive present in the landscape or ecosystem in question?

Programs based on IPM evaluate the proper control method both for effectiveness and risk. Effective, less risky invasive species controls are chosen first, including highly targeted chemicals, such as pheromones to disrupt target species mating, or mechanical control, such as trapping or weeding. If further monitoring, identifications and action thresholds indicate that less risky controls are not working, then additional pest control methods would be employed, such as targeted spraying of pesticides. Broadcast spraying of non-specific pesticides is a last resort.

Mechanical Control

weed wrench
Photo: Michelle Lawrence/Adkins Arboretum
Physical and mechanical or abiotic control includes a wide variety of devices that exclude, entrap, entangle, or electrocute insects. These methods, as simple as window screens or as sophisticated as electronic bug killers, are often more practical for individual gardeners or homeowners than for farmers or ranchers with large commercial acreage. (Meyers. NC State. 2003) People owning small acreage are able to pull or remove invasives as if they were weeding their garden. Getting down on your hands and knees and pulling by hand is a popular method for controlling: small invaded areas, plant count is low, or there are lots of helping hands. If a little more muscle is needed when pulling invasives, utilizing a weed wrench is a good idea. A weed wrench pulls the entire plant out of the ground and is a good way to make sure the plant is not coming back. If you are able to reach your invaded areas with a mower, and the pest is an annual, an option available to you is to mow the area regularly during the growing season. Continued mowing will exhaust the seed bank and overtime, you’ll notice fewer and fewer pest plants. An alternative to mowing is goats. The desired area of treatment is fenced off, goats are transported to the site, and allowed to feed on the invaded area until the invasives are gone. Just like mowing, follow up will be required to control any plants that grow back.

Chemical Control

spray
Photo: USDA Forest Service Region 8

Chemical control tactics involve a wide variety of substances that cause direct mortality (toxicants), disrupt developmental processes (growth regulators), prevent reproduction (sterilants), or modify insect behavior (semiochemicals). Conventional insecticides (the toxicants) have been a mainstay of chemical control since the late 1940's because they are convenient, effective, and inexpensive. But these compounds are not without problems. Their persistence in the environment, their effects on non-target organisms, and their tendency to select for resistance in target populations necessitate prudence in their selection as invasive species control agents. Over-reliance on these compounds (as well as occasional misuse or abuse) has drawn fire from many directions, forcing the adoption of less toxic compounds with fewer environmental side effects.

Herbicides are powerful tools, full understanding of the label is necessary for safe and effective application. Consultation with Universities, Vegetation Management Specialists or Land managers using the specific products is advisable.

  • Nonselective - Kills all species in treatment area.
  • Selective - selectivity kills only target plant type.
  • Basal stem/ cut stump - best done in late summer- targeted application to stem or to the outer portion of trunk immediately after cutting
Periodically check results and vegetation regeneration. Plan your next action.

Biological Control

Biological pest control relies upon other living organisms (parasites, predators, and pathogens) as pest control agents. These beneficial species are an important part of the ecological balance in every natural community. In some cases, biocontrol agents are reared and released in large numbers to suppress native or introduced pests. In other cases, careful management of the environment is sufficient to insure the welfare of natural enemy populations. Insect species that are accidently introduced from foreign countries often become pests because they have escaped from natural enemies in their homeland. Finding and importing these natural enemies is one important part of biological control. An example of a small scale biological control method that private landowners can use is introducing ladybeetles to eat aphids in your garden.

It is the Maryland Invasive Species Council’s hope that you will be able to responsibly employ the tactics outlined to control and improve the natural areas around your home. Enjoy the spring and summer!

For more information about Invasive Species of Concern in Maryland, visit www.mdinvasivesp.org

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