Open Space Advisory Board 2001 - Laserfiche WebLink

Home Browse Search

h r Lastoka Open Space Knapweed Study, 1997 -2001 Tim Seastedt (303- 492.3302, timothv.seastedt0colorado.edu) Findings. from The Lastoka Open Space, Boulder County: • Four years (1997 -2001) were required for small releases of biocontrol insects in a 20-40 acre area to produce a "restored prairie" at this site. • The insects needed for sustainable, environmentally friendly (low risk), low cost control were available in Colorado in 1994. Results as shown in the Boulder study could have, in theory, been shown as early as 1998. Regardless, this technique is new and not in the weed management literature, yet. • The remaining knapweed at this site is no longer part of the problem. It's 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. • The site "looks bad" and contains a high percentage of knapweed in the canopy in the year just prior to the crash of the weed. Patience is required, but in Boulder at least, the payoff was Large. • Native grasses can increase in abundance while the percent coverage of knapweed remains constant or even increases. However, this was done on a pasture where grazing was excluded. The biological wildfire attributed to knapweed may in fact be more an indication of past or current overgrazing. • 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 native asters. Some pollen consumption does occur. Insects used to remove knapweed: Urophora afnis and Urophora quadrifasciata: Knapweed seedhead gall insects. These insects have dispersed across the Front Range of Colorado and should already be present at your site. 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 -400. Phone 970 464 -7916, or contact Fred Stahl (fre ,stahk ag.rtatc.co.us). These insects have already invaded other sites in Boulder County from the Lastoka property. Cyphocleonus achates: Knapweed root weevil. Available as above. Sphenoptera jugoslavica: knapweed root beetle. Available as above The combined effects of these insects are to dramatically reduce densities of seeds. rosettes and adult (flowering) knapweed plants.