Weed of the Week – Spotted Knapweed: UPDATE

By | August 19, 2014

Spotted Knapweed

UPDATE:  We tried herbicide last week and the results weren’t all that satisfactory.  The heads of the weeds drooped, but you could tell that the entire plant had not been killed.  Here’s what a  weed expert said about that:

Spraying now probably wouldn’t be every effective (the plants are spending all their energy on seed production and wouldn’t pull the poison into the roots), but AFTER the first hard frost spraying can be very effective for about a two week window. It can also help hit the seed bank.

So although hand pulling and bagging will work right now (see more information below), spraying with herbicides probably will not.

This week’s Weed of the Week is Spotted Knapweed (centaurea stoebelbiebersteinii).  This is an erect, short-lived perennial or bennial up to 1.2 (4 feet) in height.  It has slender, wiry branches covered with fine hair supporting pink to purple towers at the tips.  A rosette is formed the first year; a flowering stalk elongates the second year.  Flowers are 1 inch in diameter and produce June through October. Seed head bracts are black-tipped with five to seven pairs of short, feathery appendages. See copies of pages from “Invasive Plants of the Crown of the Continent” below for more information.

Pretty, right?  We’ve heard stories from folks who said that they actually transplanted spotted knapweed to their yard before they knew any better.  Don’t make that mistake!

Spotted knapweed is a Category 1 noxious weed which means that it’s currently established and generally widespread.  Category 1 weeds are capable of rapid spread and render land unfit or greatly limit beneficial uses.

There are several treatments recommended.  Right now you can hand pull or dig up the entire plant, removing as much of the taproot as possible to prevent regeneration and bagging to prevent seed spread.  Cutting or mowing doesn’t really help.  Herbicides are also not very effective right now.  Wait until warm sunny days right after the first frost (September?).  When you go the herbicide route, we suggest that you contact or go by to see Linda at CHS (call at 406-755-7427 or 150 1st Ave W N in Kalispell).  She’s an expert and can help sort out what you need.

Spotted Knapweed

Spotted Knapweed

There are many important reasons for making certain that you have noxious weeds under control on your property.  First, if not controlled they can take over and crowd out the native plants.  Next, your noxious weeds will soon become your neighbors’ weeds.  In addition, invasive plans decrease suitable wildlife habitat.  And, by the way, it is the state law.  Read all about that here.

For more information about why invasive plants are every landowner’s problem, pick up a copy of “Invasive Plans of the Crown of the Continent” or other related materials made available by the NFLA Weed Committee at Sondreson Hall.  You can also get help from weed expert Linda at CHS (55 4th Ave E N, Kalispell, Mt 59901 or call (406) 755-7427).  Finally, Flathead County has a good website providing all sorts of information.  Did you know that you can rent equipment from them?  You can also call or go by to see them (309 FFA Drive Kalispell, MT 59901 or 406-758-5798) or email Director Jed Fisher at Jed.Fisher@flathead.mt.gov.

Got an idea on how to deal with the weeds?  Share it with your neighbors in the comment section below.  Want to read all of our posts about weeds, then click here.

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About NFNews Editor

Patti Hart is the editor-in-chief and founder of the NFNews.net. Patti lives on the North Fork during the summers and travels the world for the rest of the year, updating NFNews every day wherever there is an internet connection.