Rush skeletonweed, Chondrilla juncea L. is a tap-rooted herbaceous perennial Asteraceae, which is particularly prevalent in California, Idaho and British Columbia. C. juncea can reproduce vegetatively or by seed and is capable of rapid invasion of disturbed areas such as road sides, rangelands, and post-fire forestlands. Three biological control agents were released for the control of rush skeletonweed in the 1970’s: the gall midge, Cystiphora schmidti Ruebsamen (Diptera: Cecidomyiidae), the rush skeletonweed rust, Puccinia chondrillina Bubak and Sydenham, and the gall mite, Eriophyes chondrillae Canestrini (Acarina: Eriophyidae). All three biological control agents have become established and provide varying degrees of rush skeletonweed control. There are earlier reports on the efficacy of the rush skeletonweed gall midge, which was shown to be limited because of high rates of parasitism. In contrast, quantitative assessments of the impact of the rush skeletonweed rust and the rush skeletonweed gall mite on C. juncea field infestations have not yet been provided. We conducted combined mite and rust exclosure experiments at four field sites in southern Idaho to assess the impact of established biocontrol agent populations on rush skeletonweed growth vigor and cover during 2004. Rush skeletonweed mites impaired C. juncea growth vigor greater than the rush skeletonweed rust.