weeds

Biocontrol agents, such as foreign insects, can theoretically be used to control invasive, foreign plants. But scientists in Montana have found that through complex community interactions the presence of an introduced fly meant to control spotted knapweed actually accomplishes the opposite. The story goes like this:

Imported Eurasian fly infects spotted knapweed which produces galls.
Galls feed local deer mice which allows mouse population to grow.
The more numerous mice eat a larger portion of the native plant seeds.
Native plant seedlings become rarer which allows the weed to spread, and...

New research from the Georgia Institute of Technology suggests that native herbivores prefer to consume exotic over native plants. Their results imply that restoring native herbivore communities may be a viable option to help control exotic plant invasions.”  

The Nature Conservancy (TNC) was an online manual which is an excellent introduction to the subject of weed management.

Giant hogweed (Heracleum mantegazzianum Sommier & Levier) is on the federal noxious weed list making it unlawful to propagate, sell, or transport. It has the ability to displace native plants in wetmesic, sunny habitats. It is also a significant human health hazard.

Hogweed Fact Sheet, Best Practices Manual, Similar species comparison chart.

Articles and references on invasive plants.