You know your property better than anyone, so make your own weed management plan.

Natives and desirables are not nearly as competitive as weeds–weeds will quickly fill any empty niche left by herbicides.  Spot spraying will work better overall, and in the long run, since broadcast spraying also kills desirable plants.  You may get rid of one weed temporarily, but another one just as noxious will most likely take over that empty niche.  A way to avoid this is to immediately seed with a native.  Since natives tend to be slower to establish, planting a quick growing annual along with native seeds can fill that niche until the natives can establish.  Success in suppressing weed regrowth may be accomplished by planting an annual grain crop (barley is a good option) along with native seeds.  The deer and elk will browse the barley heads while pressing the seeds into the earth with their hooves (along with the added perk of fertilizing in the process).

Biocontrol insects are well established in the Bridger Canyon area.  Leafy spurge, knapweed, Canada thistle, St. Johnswort, toadflax, and common mullein all have insect populations present. (Please note that houndstongue agents are prohibited from being moved or marketed, but these insects have already migrated from their release sites in Canada as far south as Colorado.) Our climate can be quite challenging, so some years the insects may only survive and not flourish. Adding to these populations is usually not economically feasible.  Once established, the insects will move to new weed infestations on their own. 

Having an understanding of how biocontrol works will help with expectations:

• Weed-feeding insects do not eradicate weeds.  In the weeds’ original habitats (Europe and Asia) the insects have evolved along with the weeds to keep them in check–the weeds are then simply well-behaved members of the plant community.
• Biocontrol insects cannot prevent weeds–they need food, so they can only move to new infestations.
• Beneficial insects are self-perpetuating–there is no need to put new populations out year.  These agents may not always be visible, but they are very hardy.
• Biocontrol agents may be collected and moved around, but they will spread out on their own.  The insects follow their food source.
• Biocontrol agents will not spread to crops or gardens–they are host-specific to their target weed.

The Field Guide for Biological Control of Weeds in the Northwest is an excellent resource for identifying weeds and their specific beneficial insects, determining biocontrol establishment, and understanding modes of attack and life cycles.

Thanks to Cyndi Crayton for putting this article together. Also check out our Weeds page.

Fall in Bridger Canyon brings a trifecta of purple weeds: Canada Thistle, Knapweed, and Burdock. Each is obnoxious in its own special way (see our weeds page). With all the moisture we’ve had this summer, some weeds are doing really well.

If your weeds are just now blooming, you may still have some time for control. I pulled a couple stray knapweed plants this morning – the rain makes it easy. (Wear gloves – it can be an irritant.) Tall burdock and thistle stems are an easy target for a machete, and it’s kind of fun. Morning light makes them easy to spot, and it’s cool.

However, it’s generally a bit late. As plants go dormant, a lot of chemicals lose their effectiveness. If you mow mature plants, you may just wind up shattering the seeds out and dispersing them by contaminating your equipment.

There’s still one thing you can do …

Mark your weed patches for next year. You can either mark them physically, with grade stakes and surveyor’s tape, or virtually with a phone or GPS. I like the Gaia GPS app, but there are lots of other options, including iNaturalist and Google Earth. Once you have your weeds mapped out, it’s much easier to keep an eye on problem sites, and to direct control efforts at limited areas. This can save a lot of money and time, especially if you’re outsourcing chemical spraying. Accurate targeting also prevents creation of a ‘brome desert’ by chemical destruction of all flowering plants, and a more diverse field may be more resistant to future invaders.

Canada Thistle:

Knapweed:

Next year’s knapweed rosette:

Burdock – easily identified by its giant leaves and 6′ stalks: