A key economic pest of strawberries in California is the western tarnished plant bug, Lygus hesperus Knight (Hemiptera:Miridae). Alfalfa (Medicago sativa L.) is a highly attractive plant host to western tarnished plant bug, and we hypothesized that it can be successfully managed as a trap crop for pest suppression in strawberries. Completely randomized design trap cropping experiments were established on an organic strawberry farm from 2002 to 2004. Western tarnished plant bug adults and nymphs were significantly more abundant in alfalfa trap crops than in comparable edge strawberry rows. Over 3 experimental yr, twice-weekly summer vacuuming of alfalfa trap crops with a tractor-mounted vacuuming device reduced adult and nymph abundance by 72 and 90%, respectively, in trap crops. This summer vacuuming of alfalfa trap crops also significantly reduced damage caused by western tarnished plant bug in associated unvacuumed organic strawberries (June and July 2002, June 2003, and June and July 2004) compared with either an untreated control (2003) or the organic strawberry grower's standard whole field vacuuming treatment. Vacuuming of alfalfa trap crops reduces an organic grower's costs (tractor, tractor fuel, and driver time) by 78% compared with current whole field vacuuming practices. An economic analysis of a whole hectare model indicates that a positive return from the use of vacuumed trap crops could be realized in 2004. The overall potential positive net return for the 3 mo of vacuumed alfalfa trap crop treatments in 2004 was calculated at +$1,829/ha.