Chemical control involves the use of herbicides to control diffuse knapweed. The herbicide Tordon (picloram) is recognized as the most effective, but it is common to use multiple herbicides in order to reduce strain on local grasses. The herbicides 2,4-D, dicamba, and glyphosate are also effective for control. In order to be most effective, it must be applied before the knapweed plants have released their seeds, regardless of which herbicide is used. Ongoing research at the University of Colorado suggests that Tordon treatment does not contribute to long-term reductions of exotic species cover and may contribute to recruitment of other invasive species, such as redstem filaree and Japanese brome, which quickly take the place of herbicide-treated diffuse knapweed.