Managing weeds requires knowledge and persistence


By Dana Hayward
PREVIEW Columnist

Any plant can be classified as a weed if it is unwanted, out of place, unattractive, poses a health or safety hazard, hosts pests such as undesirable insects and plant diseases, or outcompetes desirable plants for water, nutrients and sunlight.

Weeds, both familiar and obscure, survive successfully in our communities as they grow quickly, produce many seeds, spread readily, have few natural enemies, are tough competitors and possess other characteristics that allow them to thrive in otherwise unfavorable growing conditions (The Science of Gardening).

Many weeds on your property and in public open spaces are part of the natural ecosystem, but others, including non-native weed species, have been introduced to their environment. Many weed seedlings appear after parent weeds have produced seeds absent of management, after seeds are transported from nearby infested areas or after seeds arrive with soil amendments or replacements. Weeds also make their way into new areas by hitchhiking on humans and animals, in irrigation water, on various types of equipment and even in packages of poor-quality seed.

One important consideration when evaluating a new or recurring weed infestation in an area is site conditions. After identifying the weed species present, consider what existing site conditions are supporting their growth and helping them to thrive. Before considering various management techniques, thoroughly evaluate the current situation and variables.

Individual weed species have unique growth habits and identifying characteristics. Some weeds are annual, meaning they complete their life cycle and produce seeds in just one growing season.

Summer annuals, including kocia, leafy spurge and redroot pigweed, germinate in the spring and produce seed in the late summer or early fall before the first killing frost. In contrast, winter annuals such as downy brome and chickweed germinate in the late summer or fall, overwinter, and resume growth in the spring prior to producing seed in the early summer.

Other weed species, such as dames rocky and musk thistle, have a biennial growth habit. Biennials require two full growing seasons to complete their growth cycle. These plants germinate in the spring, grow for a full season, overwinter and grow for another season before producing seed and perishing in a fall frost.

Lastly, weeds can be perennial, coming back year after year, reproducing both vegetatively and by seed. Simple perennials, such as dandelions, survive year after year and germinate in the spring from an existing root system. Although individual simple perennials recur year after year, they colonize new areas only through the spread of seed.

The most bothersome weeds are generally creeping perennials such as Canada thistle. Creeping perennials produce seed and spread reproductively, but also can spread and colonize new areas via above-ground runners called stolons or below-ground root systems called rhizomes.

The growth habit of various weed species dictates that certain management techniques and methods are best suited to controlling particular weeds. As such, it is critical to first identify the exact weed species you want to manage before devising a weed-management plan for your property. If you need help with identification, bring a large plant specimen into the Archuleta County Weed Management office or the CSU Extension office.

After identifying the weed species you hope to manage, review the life cycle of the plant. Understanding the life cycle of a weed is crucial for devising timely and effective management strategies that minimize economic, health and environmental risks.

Next, become familiar with the types of control available for the weed species in question and which of them will work best in the Archuleta County environment and on your specific property. Be sure of your management goals, control options and the type of weed you are dealing with before taking management action.

When identifying weeds as a first step to management and control, consider that the weeds on your property may be considered noxious weeds. In Colorado, noxious weeds are non-native weeds that effectively disrupt and disturb native vegetation and ecosystems as they have few natural controls and readily adapt to a wide range of environments.

The Colorado Noxious Weed Act requires noxious weeds to be classified as list A, B or C. List A, such as yellow starthistle, are not yet widespread and property owners are legally required to eradicate them. List B weeds, such as Canada thistle, are present in discrete populations throughout the state, and their continued spread should be stopped. List C weeds, such as field bindweed, are extremely widespread, making eradication nearly impossible.

Three overarching weed-management strategies are prevention, eradication and control. Prevention keeps weeds from occurring or increasing and is often accomplished by maintaining healthy and dense populations of desirable plants. Another prevention method is to keep weeds, especially annual and biennial weeds, from setting seed, thereby reducing the number of weed seeds in the seed bank. Keeping perennials from going to seed is not as much a preventative strategy as it is a control method, but is still inhibits the establishment of new perennial weed infestations.

Eradication entails the removal of weeds to the point that they won’t reestablish unless reintroduced to an area. It is important to establish populations of desirable plants in the place of undesirable weeds in eradication efforts. Generally, eradication is possible only in smaller treatment areas and is not cost-effective or practical for large acreages.

Control is the most common weed-management strategy and may involve cultural, mechanical, biological and chemical methods. A weed-management system is the combined pursuit of two or more of these control methods. In most situations, a combination of these methods will most effectively control the targeted weed population.

Although cultural control, such as planting competitive desirable plants like a cover crop, can be highly effective in the long term, it can often be time consuming. Mechanical control aims to disrupt weed growth via tillage, pulling, mowing and even burning plant material. These methods can produce quick results with little investment, although they have limited effectiveness on pesky perennial weeds.

Biological control involves utilizing organisms such as insects, diseases and even livestock to control weeds. While biological controls often require minimal labor and can be a long-term control solution, they are not always effective due to a wide variety of variables.

Finally, chemical control of weeds involves the application of appropriate herbicides directly to weeds or to infested areas. Chemical weed control is often fast and effective, but can have adverse environmental and health effects. Many herbicides exist, so it is important to select the correct one and apply it in a timely manner for effective control. Always follow the exact directions and heed precautions on herbicide labels; it’s the law.

As summer draws closer this year, consider what steps you can take to manage and control weeds on your property. As you begin to devise a weed-management strategy, consider the context and scale of the infestation to ensure the weed management system you plan to pursue targets the weeds you want to control, prevent or eradicate and that the chosen management strategy helps you achieve a defined land-management goal.

Information for this article was taken from Science of Gardening by David Whiting and the CSU Extension Fact Sheet No. 3.106, Weed Management for Small Rural Acreages by K.G. Beck, which can be downloaded in its entirety at

Free wildfire mitigation workshop

An on-site oak brush management workshop is set for June 26 from 10 a.m.-noon. Gambel oak is one of our most common and prolific shrubs. Learn how to manage this shrub for greater wildfire prevention. A location within the county will be identified for this hands-on training.

CPR and first aid

CPR and first aid certification classes are now being offered monthly by the CSU Extension office on the second Monday and Wednesday of each month from 6-10 p.m. Anyone needing to receive or renew certification can register by calling the Extension office at 264-5931. We will also schedule classes on additional dates with five or more registrations.

Cost for the classes is $80 for combined CPR/first aid, $55 for individual CPR or first aid and $35 for recertification with proof of current certification. The type of first aid information provided will vary by the needs of the audience.