Field experiments were conducted in 1987 and 1988 to examine interference from a natural population of perennial sowthistle on soybean and dry edible bean. In 1987, an average of 78 and 90 perennial sowthistle shoots per m2 in 71-cm (wide) crop row spacing reduced soybean and dry edible bean yield by 49% and 36%, respectively. In 1988, a year of less precipitation, an average density of 96 and 88 shoots per m2 reduced soybean and dry bean yield by 87% and 83%, respectively. One cultivation 5 wk after planting increased crop yield and decreased perennial sowthistle density compared with no cultivation. Perennial sowthistle reduced seed weight, germination percentage, and seedling growth rate of seed produced by both crops. In the presence of perennial sowthistle, one cultivation resulted in improved seed quality compared with no cultivation.
