Postdispersal weed seed predation is a significant source of weed mortalityin agroecosystems. The magnitude of seed predation, however, is variable.Understanding the relative importance of factors driving variability in seedpredation rates will increase the potential utility of seed predation tofarmers. We conducted landscape-scale field experiments to quantify andcompare the effects of space, time of sampling, and habitat on weed seedpredation. Seed predation assays, with and without vertebrate exclosures,measured seed predation rates at spatially explicit sample sites across 8.5ha of crop and noncrop habitats on a diversified organic vegetable farm inMaine. Total and invertebrate seed predation averaged 8% and 3% d−1, respectively. Vertebrate seed predators detected bymotion-sensing cameras included small mammals and birds. A ground beetle, Harpalus rufipes, was highly dominant in pitfall traps,comprising 66% of invertebrate seed predators captured within crop fields.Seed predation was randomly distributed in space. However, time of samplingand habitat were highly significant predictors of seed predation. Variancepartitioning indicated that habitat factors explained more variation thandid time of sampling. Total seed predation was greater in crop and riparianforest habitats than in mowed grass, meadow, or softwood forest. Generally,invertebrate seed predation was greatest at sites with an intermediatedegree of vegetative cover, whereas habitat type was the chief bioticdeterminant of vertebrate seed predation rates. These results suggest covercropping and wetland conservation as practices that may bolster seedpredation rates.