POSTDISPERSAL PREDATION OF VELVETLEAF (ABUTILON-THEOPHRASTI) SEEDS

Studies were conducted from 1989 to 1993 in continuous no-tillage and moldboard plow corn fields to describe rates of velvetleaf seed predat ion with time and with seed density, and to identify principal seed pr edators. Rates of seed loss from the soil surface averaged 1 to 57% da y(-1) and were equivalent in the two tillage systems. Predator populat ions were the same in no-tillage and moldboard plow fields. The predat ion rate was generally low in winter months, increased in mid-summer, and declined in late summer. In 2 of the 4 yr, predation increased in October and November. The predation rate was described by an exponenti al decay function of seed density, with high rates of seed loss at low densities and leveling off to a nearly constant level at densities ab ove 600 seeds m(-2). Predation was highest where seed access was not r estricted, and exclosures of 6.5 and 1.6 cm(2) reduced predation up to 15 and 52%, respectively. Mice were important predators in the field. In laboratory feeding studies, the carabid beetle Amara cupreolata, t he slugs Arion subfuscus and Deroceras reticulatum, and cutworms (Agro tis ipsilon) consumed imbibed velvetleaf seeds. Amara cupreolata and A . subfuscus were the only predators to damage unimbibed velvetleaf see ds.