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Spotted knapweed (Centaurea stoebe) is an invasive, perennial forb that infests rangelands in 46 US states and seven Canadian provinces. In response to high costs, environmental concerns, and health risks of applying herbicides to suppress spotted knapweed, bio-control insects and targeted sheep grazing also have been used. These two alternatives potentially could be integrated to achieve greater weed control; however, it is unknown how targeted sheep grazing affects the abundance and efficacy of spotted knapweed's bio-control insects. Some landowners have resisted applying targeted sheep grazing where bio-control insects are established for fear that sheep grazing may harm the bio-control insects. Our experiment on foothill rangeland in northwestern Montana evaluated plant and bio-control insect responses to three treatments: 1) bio-control only, 2) bio-control + targeted sheep grazing applied in late July (spotted knapweed in late bud/early flower stage), and 3) bio-control + targeted sheep grazing applied in August (spotted knapweed in late flower stage). Treatments were applied during four consecutive years (2009-2012). Targeted sheep grazing in either July or August did not affect abundance of the three bio-control insects evaluated (Larinus spp., Cyphocleonus achates, and Agapeta zoegana), but targeted sheep grazing + bio-control insects had three additive, negative impacts to spotted knapweed reproduction: 1) viable seed production by spotted knapweed was 85% less with targeted sheep grazing + bio-control insects compared with bio-control insects alone; 2) targeted sheep grazing + bio-control insects reduced total seed production below the threshold needed to sustain spotted knapweed populations, whereas bio-control insects alone did not; and 3) spotted knapweed seedling density was 68-93% less with targeted sheep grazing + bio-control insects compared with bio-control insects alone. Targeted sheep grazing and the bio-control insects we studied were compatible and, when integrated together, suppressed spotted knapweed reproduction more than bio-control insects alone.