Effect of cover-cropping systems on invertebrate seed predation

Contrasting cover-cropping systems were compared to determine whether fundamental differences in cover-cropping strategies affect weed seed predators and resulting seed predation. We conducted typical "feeding" trials in which 25 seeds of each of six weed species, including velvetleaf, wild mustard, yellow foxtail, common lambsquarters, redroot pigweed, and hairy galinsoga, were placed in the field. Exclosures showed that the majority of seed predation could be attributed to invertebrates: 43% out of a total of 56% seed predation for 11 d in 2002 and 40% out of a total of 58% seed predation for 4 d in 2003. The predominant invertebrate seed predator across all entry points of four cropping systems was a grounddwelling carabid beetle, Harpalus rufipes, which was more abundant in vegetated treatments, particularly red clover, compared with treatments recently tilled and planted to a fall cover crop. In the absence of vertebrates, H. rufipes activity– density was positively correlated with mean seed predation in 2002 (Spearman (rho) = 0.489; P < 0.001) but not in 2003 (Spearman (rho) = 0.090; P = 0.504), possibly because of a delay between pitfall trapping and predation assay. The activity– density of invertebrate seed predators measured in these systems and the high level of predation imposed on weed seeds at the soil surface indicate that cover-cropping strategies should consider late-season weed management, which maintains seeds on the soil surface and provides desirable habitat for invertebrate predators.