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Weed Management

Weed Management According to Ralph Waldo Emerson, "A weed is a plant whose virtues have not yet been discovered". This is certainly a poetic way of looking at weeds. From a gardener's point of view, however, weeds are part of the battle for a healthy, attractive landscape. Fortunately in the past forty years, we have given new life and made improvements to old methods of weed management: plant selection, mulching, watering, soil improvement, composting, nutrients, etc. Even our approach to herbicide use has become more targeted and cognizant of chemical effects on species other than the weed in question.

Educating homeowners and landscape professionals about plant selection, mulching, use of ground covers, pruning to promote plant vitality, proper herbicide use, alternatives to chemicals, and understanding the weed they fight has helped to promote a healthy approach to and success in weed management. Along with this education has come a change of attitude for many that a few weeds in a landscape will not create an epidemic and, if addressed quickly, these intruders can be controlled. Targeted use of herbicides versus broadcasting and the introduction of herbicides that breakdown faster and more completely has made chemical use safer and cheaper because less chemical is being used overall.

Too often, the term "sustainable landscape" has been associated with landscapes and yards that are weedy and overgrown and owners or managers who are lazy. While landscapes that are maintained using low inputs may have some weeds, proper selection of plant material and management will keep significant weed infestation to a minimum. As a society, it's important to change public opinion and understand that having a few weeds in a lawn or garden doesn't mean a landscape is out of control and destined to become infested with weeds. When landscapes are managed using little or no inputs, it's important to actively monitor the landscape. Monitoring includes regularly checking the landscape for problem areas and adjusting cultural practices to prevent infestations and invasions to keep plants healthy and defensive against pest populations.

Healthy, vigorous plants are truly the best defense against weed invasion. When plants are sickly, creating areas in the landscape that are bare, weeds will grow and spread quickly in these areas. Plants can become weakened in several ways. Some common reasons are:

  • The plant species and/or varieties are not adapted to the particular site conditions or imposed maintenance program;

  • Low fertility;

  • The plant has been damaged by animals, diseases, insects or people;

  • The plant has sustained damage caused by environmental stresses such as drought, lack of light,temperature, or poor drainage;

  • Fertilizers and pesticides have been used incorrectly and caused burn and other damage to foliage and roots

  • Improper pruning, mowing, etc.;

  • Plant species is a poor choice due to lack of resistance to various diseases and insects.
Before reaching for an herbicide, take time to determine the reason for the weeds. Is it lack of sunlight? Low fertility? Compacted soil? Damage? Simply killing off the weeds without understanding the reason they grew in an area in the first place might make the landscape look better temporarily, but it will not solve the problem. Sustainable landscape care revolves around using good cultural practices that promote plant health and alter the landscape features to benefit the plants and discourage weed growth.

The first step in effective management of weeds is correct weed identification and a basic understanding of the weed's lifecycle. This information will allow the landscape manager to use timing, cultural practices, and plant health to discourage weed growth. A good weed identification book and information from the local county extension will be helpful (see links below)

In the mid-twentieth century, gardeners and landscape professional used chemicals and heavy metals in an effort to control pests and diseases by eradicating them from the landscape. The result was devastating to the environment and the effects are still notable today. In sustainable landscaping and other integrated pest management programs, it is not advisable to resort to chemical means to totally eradicate pests or weeds, but to focus on managing the problem. Through education, one learns to live with a certain level of insect, weed and disease damage, and that through sound cultural practices, monitoring pest levels, and very specific, targeted chemical applications, significant plant damage can be prevented and healthy landscapes maintained without negatively affecting the environment.

Weed Identification and Lifecycles
Knowing the weeds that are competing with your desirable plants is important to understanding how to manage their populations. Weeds may be classified as grasses, broadleaves or sedges, and by their lifecycle and growing requirements: warm- and cool-season annuals and biennials, and warm- and cool-season perennials. Management is most successful when gardeners understand the best time of year to apply herbicide, mulch, etc. for effective weed management.

For example, annual weeds may germinate in the spring - crabgrass, foxtail, knotweed - or in the fall. This lifecycle difference determines when weed control methods will be most successful. Allowing 2-4 inches of mulch to remain on soil in spring will prevent sunlight from reaching the weed seeds and thus reduce germination levels. Planting ground covers that emerge early in spring and thrive in cool weather such as violets, lamiastrum and wild ginger will also compete with weeds, and reduce their vigor.

The following are websites and resources for use in weed identification:

Cultural Management Methods for Weed Control
The best form of weed management comes from altering cultural practices to favor the desirable plant material instead of the weeds. Cultural management actions may include mulching to retain water and lower plant stress, and enabling plants to defend themselves against weed infestations, insects, and disease by promoting vigor. It may include encouraging beneficial insects, or applying compost to increase nutrients available to the desirable plants.

There are several basic things one can do to reduce weed populations in a landscape and garden area without the repeated use of herbicides. Mulching, proper plant selection, improved soil quality, proper watering technique, and maintaining plant health are five areas that will help keep weeds at a minimum, and reduce the amount of weeding and maintenance required.

Mulch not only improves moisture retention of soil, but it can significantly reduce weed populations. When applied correctly, mulch reduces the sunlight to weed seeds decreasing their germination rate. This results in less nutrient competition and less weed maintenance for the gardener and landscape professional.

Properly selected and managed ground covers are good choices for weed management, especially in areas where turf grass doesn't grow well or in areas that are difficult to maintain. Proper care of ground covers can encourage them to create a dense vegetative mat that shades the soil surface and prevents weed seeds from germinating. They also compete with weeds for nutrients, moisture and space. Some ground covers can become invasive, but if properly maintained, ground covers can be an attractive form of weed control.

When choosing a ground cover specifically for weed control, it is especially important to consider the site conditions. Landscape grasses are a good choice as ground covers for tough, weed-prone areas. They can sustain poor soils, tolerate sun, and they have deep root systems so they are good for erosion control. Grasses are generally low maintenance, and many need not be mowed, and can be mixed with native flowering plants for a prairie-like effect.

For information about weed control specifically for wildflowers, visit Weed Management for Wildflowers from the North Carolina University Extension.

Pruning for Weed Control (FUTURE)

If an herbicide is required to prevent an invasion, it is important to first read and follow the label directions exactly as stated on the product container. The label provides necessary information regarding proper product application and container disposal procedures. Labels are legal documents which are enforceable by law should the product be used in a manner inconsistent with directions.

Herbicides should be targeted only at the weed(s) they are designed to eradicate. They are classified as selective and non-selective, and pre-emergent and post-emergent. Break-down processes and plant absorption are particularly important as they account for removal of pesticides from the environment. Once applied, herbicides may be broken down by sunlight, by microbes, by chemical action or by a combination of these. Other herbicides may be evaporated into the atmosphere, absorbed by plants, or may cling to soil particles. For a summary of common weeds and their control using herbicides, visit Weed Management at this website.

Some desirable plants are loosely related to the weeds that compete with them for resources. For example, herbicides for perennial grassy weeds such as quack grass cannot be used in an area planted with landscape grasses because they are non-selective herbicides and applications will kill the desired landscape grass as well as the weeds. Therefore, weeds (especially perennial weeds) must be eliminated as much as possible prior to planting. Subsequent hand-weeding and mulching will be required to control weeds. Herbicides selective for broadleaf weeds such as dandelions and plantain may be used in plantings of landscape grasses.

Pre-emergent herbicides can be used to control annual weeds in mass plantings of established ground covers. It is important to consult the label when determining if a chemical can be used on a specific plant and is appropriate for the type of weed you are trying to control. If perennial weeds are a problem, fumigating the soil prior to planting may be a solution. Be sure to read and follow all directions on the label, and wait the appropriate length of time before cultivating the soil and planting.

Understanding Labels (FUTURE)

Alternatives to Chemical Herbicides (FUTURE)


Cornell University, "Plan Before You Plant: A 5-Step Process for Developing a Landscape Weed Management Plan", Joseph C. Neal, Weed Facts, publication #5.

Ecological Agriculture Projects, "Weeds as Indicators of Soil Conditions", publication #67, Stuart B. Hill and Jennifer Ramsay, 1977.

"Indicator Weeds", Tristate Biosystems, online information.

Manitoba Agriculture and Food, "Weeds, Insects and Diseases", March 2001.

North Carolina Cooperative Extension Service, "Weed Management for Wildflowers", leaflet # 645, Lena Gallitano, W.A. Skroch, and D.A. Bailey. September 1993.

Ohio State University Extension, online Fact Sheet, "Poison Ivy Identification and Control", HYG-1015-96, Cindy Welyczkowsky Jane C. Martin.

Purdue Landscape and Nursery Thesaurus. Maintained by Bruno Moser, December 4, 2001.

Purdue University Cooperative Extension, "Diagnosing Herbicide Injury on Landscape Plants", ID-184, Melodie Putnam, Dan Childs, Gail Ruhl and B. Rosie Lerner. 1993.

United States Department of Agriculture, "Regulated Noxious Weeds: State List". Updated December 7, 2000..

University of Illinois Cooperative Extension, "Weeds of the North Central States", online publication.

University of Nebraska Cooperative Extension, "Where Do Weeds Come From?", G86-807-A, Robert G. Wilson and John Furrer, September 1996.

University of Minnesota Extension, "Ground Covers for Rough Sites", FS-1114-GO, Mary H. Meyer and Michael E. Zins. Revised 1998.

University of Minnesota Extension, "Weed Control in Home Gardens", Deborah Brown, Yard and Garden Line News, Volume 2 Number 4, April 1, 2000.

University of Minnesota Extension, "Corn Gluten Meal: A Natural Pre-Emergence Herbicide", Yard & Garden Brief, Jean Gilligan and Deborah Brown.

University of Minnesota Extension, "Broadleaf Weed Control", INFO-U publication #531, Bob Mugaas and Brad Pedersen. Revised 1998.

University of Minnesota Extension, online information, "Weed Identification", VegEdge, February 21, 2002.

University of Minnesota Extension, "Annual Grass and Perennial Weed Identification", MI-1352-GO, Gerald R. Miller and Oliver E. Strand. Reviewed 1997.

University of Minnesota Extension, "Establishing and Maintaining a Prairie Planting: Weed Control", FO-6748-GO, John F. Kyhl, Mary H. Meyer, and Vera A. Krischik, 1997.

USDA - Forest Service, "Listed Noxious Weeds and Invasive Non-Native plants - Eastern Region", Ian Shackleford, Eunice Padley, and Jan Schultz. September 1998.

"Weeds and Weed Management", Michigan Electronic Library, online information. 2002.

Royer, Frances, and Dickinson, Richard, Weeds of the Northern U.S. and Canada, Lone Pine Publishing - Renton Washington, and University of Alberta Press - Edmonton, Alberta. 1999.

Weisenhorn, Julie, Manual for Hennepin County Sustainable Landscape Site, Hennepin County Environmental Services, December 2001.

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