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.

No abstract

One year after the last of six annual applications of 3-(p-chlorophenyl)-l,l-dimethylurea (monuron) at 2.4, 3-(3,4-dichlorophenyl)-l,l-dimethylurea (diuron) at 2.4 and 7.2, and 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 1.0 and 3.0 lb/A in a furrow-irrigated vineyard on Warden silt loam, a bioassay using oats (Avena sativa L., var. Kanota) as the indicator showed that 1.6, 2.8, 10.6, 0.6, and 2.0 lb/A, respectively, remained in the surface 12 in of soil. Of the total, 62 to 89% was located in the surface 2 in and 86 to 100% was in the surface 4 in. Three years after the last of four annual applications of monuron at 7.2 lb/A, 0.8 lb/A remained in the surface 12 in.

Irrigation laterals PL.15.LR and S2.15W, in the Yakima Valley of Washington and the Columbia River near Paterson, Washington, were sampled for weed seeds during 1970, 1971, and 1973–74, respectively. Weekly or biweekly screenings of the water in the three systems during the irrigation season yielded seeds of 137, 84, and 77 plant species, respectively. In the same order, the total number of seeds per 254 kl of water averaged 2,220, 682, and 292 for the season. Moreover, if the seeds were evenly distributed in the average amount of water used to irrigate the land during the season, the number of seeds disseminated would average 94,500, 10,400, and 14,100 per hectare. Weed control practiced by water users along certain sections of S2.15W markedly reduced both the kind and number of weed seeds found in the water when compared with PL.15.LR on which no weed control measures were used.