This procedure is recommended for areas with established infestations of diffuse knapweed. Areas just being invaded or containing only small populations of the weed may be controlled by other methods. Colorado law requires containment weed on your property during the restoration process. Some means of keeping the weed from tumbling onto uncontaminated areas may be required.

The insects needed for sustainable, environmentally friendly (low risk), zero cost control were available in Colorado as early as 1994. Up until our study, however, these species were not tested for their impact on diffuse knapweed. Thus, this technique is "new" and is just now reaching the weed management literature.

Four years (1997-2001) were required for small releases of insects in a 20-40 acre area to produce a "restored prairie" at this site. Knapweed was reduced below levels recommended as acceptable by The Nature Conservancy (TNC) guidelines, and to levels that are certainly acceptable under Colorado law. Even with weed remaining on-site, it's little to no threat to adjacent areas.

The remaining knapweed at this site as of 2001 was no longer part of the problem. It's now part of the solution. Therefore, not all knapweed is 'noxious' ; the weed on this site is a fly/beetle/weevil incubator. Tolerance of the presence of the weed is part of the sustainable control process. A few weeds on-site maintain the insects and therefore maintain the long-term, sustainable control mechanisms.

The site "looks bad" and contains a high percentage of knapweed in the canopy in the year just prior to the reduction of the weed. Patience is required, but in Boulder County at least, no additional control methods for prairie sites appear necessary.

To date, no negative interactions between the insects released to eat knapweed and the native vegetation at this site have been recorded. We've been unable to entice these insects to eat other plants, and the closest native relatives of the knapweed (the plants most likely to be attacked) have greatly increased during the restoration process.

 Insects used to remove knapweed:

1. Urophora affinis and Urophora quadrifasciata: Knapweed seedhead gall flies. These insects have dispersed across the Front Range of Colorado and should already be present at your site.

2. Larinus minutus. The knapweed seedhead weevil. These are available free from the State of Colorado, Dept. of Agriculture, Biological Pest Control Section, Palisade, CO, 81526-0400. Phone 970 464-7916). These insects have already invaded other sites in Boulder County from a number of release sites. This insect may be the most important of all in reducing knapweed populations.