SEASONAL EMERGENCE AND PERSISTENCE OF GREEN FOXTAIL

Green foxtail, Setaria viridis (L.) Beauv., emerged at the same time in the spring as the wheat Triticum aestivum L. This was attributed to faster growth of green foxtail when the soil warmed up and its emergence from shallower depths than the wheat. There was a flush of emergence in the spring. Subsequent emergence appeared to depend on rainfall but some seedlings emerged in every 2-wk period throughout the season and in some years as late as October. A buildup of seeds occurred with the 3-yr rotation, i.e., when wheat was sown as a second crop. Germination was primarily controlled by temperature. No germination occurred in 10 days at 4.4 C and only a limited amount at 10 C. Eleven to 26% of the seeds in the soil and 7% of those on the surface were viable after 4 yr. Persistence increased markedly with depth, which emphasizes the need for shallow tillage. Primary dormancy disappeared rapidly. Secondary dormancy was detected thereafter in as many as 24% of the seeds.