Squarrose Knapweed

During the late 1800’s and early 1900’s the Tintic Valley and surrounding mountains were booming with gold and silver mining. The valleys raised dryland wheat which was stored in the area silos and later shipped to different mills for processing.

The aggressive Squarrose Knapweed had destroyed much of the native vegetation and in many areas created a near monoculture of knapweed. Because of this weed the area is no longer used for dryland farming and grazing has been greatly reduced. The long-term impact from this weed invasion is the loss of vegetative biodiversity which affects:

• Deer, pronghorn antelope, wild horses, sage grouse, and other wildlife habitat
• Cattle and Sheep grazing
• Crop production and marketability
• Water quality and Water quantity
• Recreational opportunities
• The natural beauty of the land

If not controlled, this invasive plant could spread like a wildfire throughout the West Desert ecosystem of Utah and Nevada destroying millions of acres of public and private lands.

Squarrose Knapweed (centaurea virgata)

Background: Squarrose knapweed is a native plant of the Eastern Mediterranean area. It is very destructive to natural areas in the west. Knapweed releases a chemical substance reducing competing vegetation.

Description:  This long-lived perennial grows 12 to 36 inches tall. The rosette and stems have deeply lobed leaves. Flowers are rose pink. It is often confused with diffuse knapweed but differs in that the toothed flower bracts are curved outward and are not laterally toothed. Bloom occurs in early to mid-summer.

In the 1950’s a new plant was found growing in the dryland wheat, it was identified as Squarrose Knapweed. Squarrose Knapweed is a very aggressive and highly competitive rangeland weed probably introduced from contaminated seed.

In 1954 a meeting was held with landowners and government representatives to discuss concerns regarding the plant. For the next 30 years no major control efforts were used to eradicate the weed. The disturbed areas around the mines soon became infested; farming practices and livestock and wildlife soon spread the plant across the range. In the early 1990’s it was estimated that nearly 200,000 acres were infested with the plant.

In 1996 a group of concerned agencies and others met to discuss the major problem that the weed had become. As a result of the meeting the group organized the Squarrose Knapweed Cooperative Weed Management Area.

The group decided the first step for a successful program was to develop a management plan which included:

• Inventory of the Squarrose Knapweed using GPS technology
• Monitoring plans
• Research to understand the plant and identify the best methods to control it 
• Education for land managers, producers and general public
• A plan to attack the weed from the outer perimeter

If not controlled, this invasive plant could spread like a wildfire throughout the West Desert ecosystem of Utah and Nevada destroying millions of acres of public and private lands.

In the early 1990’s, a more coordinated effort was undertaken to address the Knapweed invasion. The counties and the agencies began to coordinate their efforts by developing a plan of attack the weed. A solid management plan was developed and implemented across the CWMA.

Closely following our management plan we implemented multiple treatments.

The most effective method to control Squarrose Knapweed is by using herbicide. Utilizing multiple cooperative spray days, we all came together and successfully treated 80,000 acres. We were able to apply herbicide via aerially spraying, and through the use of 4-wheelers and trucks outfitted with heavy duty tanks.

Biological control of weeds is the deliberate use of living organisms to limit the abundance of a target weed. It seeks to reunite host-specific natural enemies from the weed's native range with the target weed. Biological control agents may feed on a weed's flowers, seeds, roots, foliage and/or stems. This damage may kill the weed outright, reduce it's vigor and reproductive capability, or facilitate secondary infection from pathogens- all of which reduce the weed's ability to compete with other plants.

As part of our integrated weed management plan, we implemented biocontrol as a treatment method. We conducted multiple biocontrol days where we collected the biocontrol agent and then released it on various weed infestations. Some of these areas have already shown a 50% reduction in plant density.

Often, once the weeds are controlled, an area will need to be reseeded or replanted. This is done to create healthy, competitive vegetation that will help resist invasion. This helps re-establish the areas to a desired state.

As part of our integrated weed management plan, we were able to re-seed 26,000 acres, helping to bring the landscape back to a desirable state.