Cecidophyes rouhollahi, a European gall mite, has been screened and approved for release in Canada as a biological control agent for false cleavers, Galium spurium L., an introduced weed that is becoming increasingly abundant in canola and other annual crops in the prairie provinces of Alberta, Saskatchewan and Manitoba. Field plot studies were conducted in Alberta in 2003 and 2004 to evaluate its survival under field conditions, impact on the weed, dispersal, and effects of timing of application. Results in 2003 were inconclusive due to late plot setup and low numbers of mites available. In 2004, mite treatments resulted in approximately 30% reductions in seed yield and biomass of false cleavers, growing either alone or in a canola stand. Early inoculation of mites (at the 2 leaf-whorl stage) resulted in heavier galling and greater reductions in biomass than inoculation at the 6 leaf-whorl stage. No evidence for overwinter survival of the mites in the field has yet been seen.