Knapweed

Knapweed is a prohibited noxious weed that is found in pastures, cultivated fields, roadsides, railroads and disturbed areas. As a prohibited noxious weed, it must be eradicated if found in Alberta.

There are several types of knapweed, with 3 of them being more common in the MD of Taber: Diffuse Knapweed, Russian Knapweed, and Spotted Knapweed. Knapweed plants can grow up to over 1m in height and the stems are generally very branched, depending on the species. Plants can appear bush-like or be quite slender.

All 3 species of knapweed common in the MD of Taber grow a similar flower that varies in colour; Diffuse Knapweed flowers are usually white but can be rose or purple, Russian Knapweed flowers are typically pink to purple, and Spotted Knapweed flowers are usually pink to purple but can sometimes be white. The flowers of all 3 species are fairly small, only about 1-2 cm across. Flowering occurs between June and October.

Knapweed seeds are fairly small and can remain viable in the soil for up to 10 years, so it is important to control the plant before it flowers and to revisit sites of infestation for several years to maintain control.

Control



While knapweed is difficult to control, there are several herbicide products that are registered for control of knapweed. Always be sure to check the pesticide label for proper use and to ensure it is registered for use on knapweed. Always read and follow the pesticide label directions.

Mowing and hand-pulling can be effective methods of control in smaller infestations, especially before seeds are set. Be sure to pull up as much of the root as possible to prevent regrowth. Maintaining healthy pastures and rangelands, as well as cleaning equipment before transport can help to reduce the spread of this weed.
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