Seed-predators reduce broadleaf weed growth and competitive ability

Abstract

Based on field observations that fewer broadleaf weeds were found in low-input no-tillage systems (LINTS), a series of greenhouse experiments was conducted to investigate the effect of weed seed-predators on the competitive ability of broadleaf weeds grown with grass weeds. Two major broadleaf weeds, which were found in LINTS, red root pigweed Amaranthus retroflexus and lambsquarters Chenopodium album, and two major grass weeds, large crabgrass Digatara sanguinales and fall panicum Panicum dichotoflorum were tested singularly and in pairs (always one broadleaf with one grass) in the study. These seed pairings were exposed to (1) seed-predators (carabids and field crickets found in LINTS) which were at different densities, (2) wheat straw residue, (3) seed-predators and residue, and (4) a control (no seed-predators or residue). Seed-predators reduced the plant relative yield (PRY) of broadleaf weeds to the same extent as the wheat residue. Seed-predators preferred to feed on the broadleaf seeds which reduced the broadleaf weeds competitive ability when grown with grasses. Decreasing seed-predators by 50% resulted in almost no change in broadleaf plant relative yields compared with the control (no seed-predators). The decrease in seedling PRY caused by seed-predators was still evident as the plants matured. There was a significant interaction between seed-predators and residue in reducing broadleaf PRY probably because of differing effects of each on plant growth.