Ethylene gas (C2 H4) was found to stimulate the germination of witchweed [Striga asiatica (L.) O. Kuntze] seeds. Ethylene diffuses greater than 120 cm horizontally from point of injection and more than 90 cm below the soil surface. Rates of 0.42 kg/ha induced germination of witchweed seeds in sandy soil; but 1.1 kg/ha is required on a heavy clay soil. Witchweed seeds respond to ethylene after a period of preconditioning that is necessary to break dormancy. Under field conditions in the Carolinas, maximum response of seeds to ethylene occurs between late April and late July. Field studies indicate a 90% reduction in viable witchweed seeds occurs where a single treatment with ethylene has been applied. The use of ethylene appears now to be a major contributor toward the eventual eradication of witchweed from the United States.

Seeds of barnyardgrass [Echinochloa crus-galli (L.) Beauv.], green foxtail [Setaria viridis (L.) Beauv.], and yellow foxtail [Setaria lutescens (Weigel) Hubb.] were buried 2.5, 10, and 20 cm deep in irrigated and nonirrigated sandy loam. Samples were exhumed periodically for 15 yr to determine viability. Viability declined with time. Three percent or less of the seeds of each species remained viable 13 yr after burial, and none were viable after 15 yr. Survival of seeds under apparently uniform conditions varied extremely. Thus, subtle differences in environmental conditions profoundly affect longevity of seeds.