The Bluff is home to a fine array of native plants -- and also to many noxious weeds.
A noxious weed is a non-native plant in an area. Usually they are invasive, meaning they spread rapidly as no animals in the area feed on them. Consequently they crowd out native species and reduce the food and habitat available for wildlife. Some, but not all, noxious weeds are poisonous.
Noxious weeds found on the Bluff include Knapweed (Spotted and Diffuse), Rush Skeletonweed, Common Bugloss, Hawkweed (Orange and Yellow), Scotch Broom, Scotch Thistle, Poison Hemlock and Dalmatian Toadflax.
Find pictures of these weeds at:
Helpful volunteers can contribute to control by pulling Knapweed when the soil is moist. Other species, such as Rush Skeletonweed and Dalmation Toadflax, have extensive underground root systems that are stimulated by cutting or pulling – so we do not recommend pulling these species.
Noxious weeds may be introduced into an area in a variety of ways, including by human beings who may transport weed seeds attached to their clothing, in the mud on their shoes or bike tires, or in their pets' fur.
Click here for a brochure on how to prevent transporting noxious weed seeds!
The Friends of the Bluff uses an integrated approach to managing noxious weeds - choosing a combination of the best methods available.
1. Biological control
Introducing an insect which feeds ONLY on a specific weed and doesn't bother any other plants or animals
a. Cyphocleonus achates - the root weevil of spotted knapweed (above) was released at Polly Judd Park on September 2, 2011. It may reduce knapweed populations over time as the beetle larvae eat out the root crowns of knapweed.
b. Mecinus janthinus - the stem weevil of Dalmatian toadflax has been released in other parts of Spokane County and moved on its own to the Bluff. It is a effective biocontrol species, and while this control method will not eradicate a weed species, toadflax plants have become sparse on the Bluff.
c. A gall midge and a gall mite of Rush skeletonweed have also moved into the Bluff area, and Friends of the Bluff have worked to spread them around. However, while these insects may reduce seed production they don't decrease populations of existing plants.
2. Mechanical control
Pulling Knapweed (get all the root) is labor intensive, but can work well. Wear gloves and long sleeves, as the plant is considered allelopathic (stunts or kills other species growing around it) and some people experience rashes after contact.
Cutting back Scotch Broom can be a precursor to pulling with a weed wrench or herbicide application.
Biennials like Scotch Thistle can be controlled by chopping them out before seed formation.
3. Preserving the natural landscape and plantscape
Large areas of the Bluff are weed-free because they have been only lightly touched or spared disturbance by vehicles and trails. Noxious weeds don’t gain a foothold in a healthy, natural forest floor or prairie.
Reseeding with native grasses (done in some areas of the Bluff in the fall of 2013) can help restore damaged areas. The Spokane County Noxious Weed Control Board funded purchase of native grass seed for this purpose.
4. Herbicide application
The City of Spokane and City Parks retain a licensed applicator who treats a few, limited, noxious weed concentrations; Hawkweed, Common Bugloss, and Poison Hemlock being examples. The City has authorized Poison Ivy control along trails as well.
Friends of the Bluff board members authorized purchase of herbicides glyphosate and Milestone for use in limited weed control efforts. These have been authorized through written permission from City Parks.
Herbicide based control is only attempted after a thorough review of native plants. Every effort is made to avoid harming natives. Milestone acts only on broadleaf plants. Late fall application suppresses winter annual grasses, a good thing.
Glyphosate has been used as follow up to the control of Common Bugloss by the City contract applicator, and was applied in late fall and early spring on the leaves of Bugloss rosettes.
Milestone has been used in Bugloss control as well as on (trailside) concentrations of Knapweed and selected test plots of Rush Skeletonweed.
Skeletonweed (SK) is particularly difficult to control as it spreads both by seed dispersal (think up to 20,000 tiny dandelion seeds per plant) and vigorous root rhizomes.
Skeletonweed test plots were placed where native grasses were invaded by SK. Most Skeletonweed plants were infested with Gall Mites, which weaken the plants and aid in herbicide control. Spring and fall herbicide applications seem equally effective, about 80%. Perennial grasses appear to grow well following the cheatgrass and SK control.