Predispersal seed predation of redroot pigweed (Amaranthus retroflexus)

Abstract

Field experiments were conducted in 1999 and 2000 to determine if (1) seed predation of redroot pigweed plants occurred in agricultural fields, (2) corn-cropping patterns could be manipulated to influence the quantity of weed seed predation, and (3) alterations in corn canopies affected the microenvironment, possibly influencing predator populations. Corn was planted in standard (75 cm) or narrow (37.5 cm) rows with corn population densities ranging from low to very high (2.5 to 10 plants m−2). The extent of seed predation occurring on terminal weed inflorescences in the treatments was evaluated. Predation levels of redroot pigweed were highly variable spatially and temporally. Coleophora lineapulvella Chambers (Lepidoptera: Coleophoridae) was the dominant predator of redroot pigweed seed. Seed predation was higher in 2000 than in 1999 (P < 0.05). On average, C. lineapulvella larvae attacked 11% of the inflorescences in 2000 and 3% of inflorescences in 1999. The proportion of damaged seeds per attacked inflorescence was as high as 93% in 2000 but only 42% in 1999. Row spacing and corn density did not affect levels of weed seed predation (P > 0.05). But canopies of closely spaced corn increased shading to redroot pigweed plants growing below the canopy, consequently decreasing total weed biomass and seed production.