Biological management of noxious weeds has continued to grow as more biological control agents are made available.
Leafy Spurge was the first noxious weed on which biological control insects were released. In 1991, a little Flea beetle (Aphthoma flava and Aphthoma nigriscuris) were released on some dense infestations of leafy spurge in the Tallahassee Creek drainage. The results of the releases have been favorable, after 12 years, the leafy spurge has been reduced by 60 percent. After the initial releases, subsequent releases were made until 1998. The population of beetles has reached levels that has allowed the area to be used as an insectaries, each year significant numbers of these beetles are captured and moved to other leafy spurge sites within the county.
Musk thistle is the second noxious weed in Fremont County to be targeted for biological control. In 1993, a small seed head weevil (Rhinocyllus conicus) was released on a dense musk thistle patch in western Fremont County. Since that humble beginning, this weevil has been distributed and spread through out the region and has been an effective tool in the control of musk thistle.
Many other species of insects, stem weevil (Ceutorhynchus litura) (Trichosirocalus horridus) have been released on Musk, Scotch and Bull thistles and have been found to be somewhat effective; however, insects released on Canada thistle (Ceutorhynchus litura) (Larinus planus) (Urophora cardui) have shown no appreciative results.
Dalmation Toadflax is another of the noxious weeds that insect releases have been done. In 2001, a small release of Stem Boring weevil (Mecinus janthinus) was made on a small infestation of dalmation toadflax along Four Mile Creek. Because insect releases take an average of three years before results can be seen, it is not known how well this insect will do.
Releases of Knapweed Flower weevil (Larinus minutus) have been made on Diffuse Knapweed in the Copper Gulch and Cotopaxi areas. The releases were done in 2001, 2002 and 2003. The results of these releases are not yet known.
Fremont County will test new control agents as they become available and will continue to use those that have proven effective.