Weeds 101

If a poll were taken, we probably would find local residents categorizing weeds differently. Some would say their little blackberry patch is not a noxious weed, but a highly valued provider of blackberry pies. Some would say their English ivy stabilizes their bank and is not a noxious weed. Some would say their field of Scotch broom is not a problem unless it encroaches onto their manicured landscaped areas.

Some would consider City of Portland ridiculous when listing lemon balm, vinca, Robert geranium, and English holly on their Nuisance Weed List. It may be hard for some of us to face up to reality of what some of our old weed friends do to the native habitat of our area. Some “bad” weeds are so prolific that some would guess they had to be native to the area. Beauty is not always benign. Be cautious of gardening articles that promote the attraction pf wildlife. Do not choose plants that could be a problem where you live, no matter how much the birds may enjoy it, as birds are unknowing transporters of seeds over vast areas.

In a recent survey of 75 Portland parks and natural areas, the top ten most widely spread invasive species of plants observed were Himalayan blackberry, English holly, English ivy, English hawthorne, sweet pie cherry, traveler’s joy (Clematis vitalba), English laurel, common filbert, Norway maple and bittersweet nightshade. All of these species can be found in Forest Park; some more concerning than others. We asked Sandy Diedrich of Forest Park’s Ivy Removal Project what she considered the top five worst weeds affecting Forest Park. She clarified that one must factor in a weed’s ability to spread, ease of control, and affect on native species. Then, she quickly named off the top four worst weeds from her point of view: English ivy, Himalayan blackberry, clematis, and garlic mustard. A number of species competed for her fifth choice: Norway maple, Scotch broom, knotweed and butterfly bush. Not all invasive and/or nuisance weeds are equal in her mind.

When working a larger area with multiple species of weeds, prioritize your work and your weeds. Know which weeds are highly competitive, which are moderately competitive, and those that are slow growing and not competitive with native plants.

Noxious Weeds

“Noxious Weed” is a legal term. It is not simply a weed that causes personal annoyances. By legal definition, “Noxious Weed” means any plant designated by the Oregon State Weed Board that is injurious to public health, agriculture, recreation, wildlife, or any public or private property. Noxious weeds form dense monocultures through which no other plant can grow. They crowd out native plants and leave nothing for most native animals to eat. The Oregon Department of Agriculture (ODA) rates and classifies weeds at the state level. Classification prioritizes noxious weed control programs. Each Noxious Weed is placed into one of the following three categories:

“A” Designated Weed: a weed of known economic importance which occurs in the state in small enough infestations to make eradication/containment possible; or is not known to occur, but its presence in neighboring states make future occurrence in Oregon seem imminent. Infestations are subject to intensive control when and where found.

“B” Designated Weed: a weed of economic importance which is regionally abundant, but which may have limited distribution in some counties. Where implementation of a fully integrated statewide management plan is not feasible, biological control shall be the main control approach. Some weeds in this category are quickly spreading in our area: Scotch Broom, Butterfly bush, English ivy, Giant horsetail, Himalayan blackberry, Johnsongrass, Knotweeds (giant, Himalayan, Japanese), Poison hemlock, Tansy ragwort, and Thistles (including bull, Canada), Field bindweed (field morning glory).

“T” Designated Weed: a priority noxious weed designated by the Oregon State Weed Board as a target on which ODA will develop and implement a statewide management plan. “T” designated noxious weeds are species selected from either the “A” or ”B” list. Tansy ragwort which is in this category and is of particular concern for our local horse and livestock owners since is it toxic to them.

(Source: ODA & Noxious Weed Control Program’s 2004 Noxious Weed Policy & Classification System)

Invasive Weeds

The decision to classify a non-native plant as “noxious” tends to be based more on its harm to agriculture rather than harm to the environment. If not classified as a “noxious weed”, this does not necessarily mean that plant cannot cause harm to the environment. In other words, both noxious and invasive weeds can cause significant harm.

Invasive weeds are plants that have been introduced into an environment outside their native range. In their new environment, they have few or no natural enemies to limit their reproduction and spread. Because they have no natural enemies and the environment is right, if we let their spreading be left unchecked, it may be impossible to control them in the years ahead. Invasive weeds are considered to be the second most important threat to biodiversity, after habitat destruction.

Some invasive weeds are classified as noxious weeds by ODA. While some nonnative plants are invasive, others are not. Invasive weeds affect all of us, whether we are landowners, tree farmers, animal owners, taxpayers, hikers, or allergy sufferers. They reduce crop yield, quality, and value. Some are toxic to animals and humans.

Nuisance Plants

The City of Portland has placed about 143 plants on its “Nuisance Plant List.” They are considered a nuisance because of their tendency to dominate plant communities, and/or are considered harmful to humans. These plants may be native, naturalized or exotic. They can be removed by the landowner without environmental or greenway review by the City. Other local, state or federal laws may still regulate removal or certain plants on this list.

Weed Resources

• Pacific Northwest’s Least Wanted List: Invasive Weed Identification and Management. Oregon State University Extension Service. Publication #EC1563. June 2003. $5.
• 2004 Noxious Weed Policy & Classification System. Oregon Department of Agriculture Noxius Weed Control Program. Availabile at www.oda.state.or.us or call (503) 98604621.
• Northwest Weeds: The Ugly and Beautiful Villains of Fields, Gardens, and Roadsides by Ronald J. Taylor. Mountain Press Publishing Company. 1990.
• Federal Noxious Weed List: www.aphis.usda/ppq/weeds
• Oregon Noxious Weeds (Oregon Department of Agriculture):
http://egov.oregon.gov/ODA/PLANT/weed_index.shtml or (503)986-4621
• The Nature Conservancy: http://www/tncweeds.ucdavis.edu/
• West Multnomah Soil & Water Conservation District: Website at www.wmswcd.org then click on “resources” or call (503) 238-4775. Excellent links on website.
• Metro has excellent pamphlets on weeds and all sorts of topics. www.metro-region.org or (503) 797-1700.
• Portland Plant List: www.portlandonline.com and search Portland Plant List & Portland Online
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