News and Opinion from Sisters, Oregon

Battling invasive weeds in Sisters

There is a weed among us, and we need to be on the lookout for it because, left to its own devices, it will take over our fields, gardens, public rights-of way, and stream beds.

Knapweed (Centaurea maculosa) fools some people because it looks like a wildflower — but “wild” is the operative word.

When the flowers of the weed are through blooming, which is about this time of the summer, they form fluffy white seed heads that blow in the wind, leading to approximately five million acres in the U.S. infested with knapweed. These groups of weeds (there are seven varieties) are highly competitive and invasive, crowding out native plants. They create havoc on Western rangeland and invade pastures and fields in the Midwest and Eastern states.

Oregon is the adopted home of six different knapweeds and here in Sisters the spotted knapweed is the one causing trouble. It is tough to control, spreads its seeds easily, and requires aggressive eradication efforts. The best time to deal with them is when they are nothing more than a small broadleaf rosette and can be pulled. If they have already gone to seed, if there are only a few, very carefully pull them by hand so as to not spread the seed.

There is a great deal of knapweed information on the internet. For larger areas of knapweed, biological control using insects is proving very effective. Each knapweed species has biological enemies (insects) that attack different parts of the knapweed at different times of the year. For example, knapweed flower weevil larvae feed in the seed heads, destroying the knapweed seeds before they mature. The biological control agents can be ordered online.

Spotted knapweed is a perennial herbaceous plant that grows two- to three-feet tall and produces light purple flowers. People who don’t know what a noxious weed they are have been known to cultivate them in their yard.

Knapweed is a native of Europe and Asia. It was introduced to North America in the 1890s as a contaminant in agricultural seed and through soil discarded from ship ballast. It has become a serious problem in pastures and rangeland in the western U.S. and Canada. Cattle avoid eating it and, if it invades, it will reduce usable grazing land. What we do or don’t do can have consequences for people we don’t even know.

Spotted knapweed can be found growing in places like gravel pits, railroad beds, and field margins, from where it can spread to adjacent intact woodlands and prairies. A prime example of a knapweed infestation can be seen in Sisters in the field at the corner of Camp Polk Road and West Barclay Drive. The City is currently working with the property owner to find a way to mitigate the situation.

The City of Sisters addresses noxious weeds like spotted knapweed in the Sisters Municipal Code, 8.15.060 (2) (a) (i and ii) which reads:

(2) Weed and Brush Removal. The owner or person responsible for the care of any property located in the Sisters city limits shall:

(a) Remove or destroy all invader weed species, including but not limited to knapweed, Russian and domestic thistle, Scotch broom, and cheat grass from private property, as follows:

(i) All invader weed species that are in flower shall be hand-pulled and bagged, and subsequently removed from the premises.

(ii) If not in flower, by using the most efficient and practical means available. [Ord. 479 § 3 (Exh. A), 2017; Ord. 444 § 1 (Exh. A), 2014; Ord. 282 § 1, 1997. Code 2002 § 8.12.042].


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