Influence of Planting Date on the Growth of Johnsongrass (Sorghum halepense) from Seed

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Abstract
Seed of johnsongrass [Sorghum halepense (L.) Pers.] were planted during 1976 and 1977 at monthly intervals from March through October to study the growth and reproductive habits of this weed at Shafter, California. Plants were grown for 12 weeks and harvested at 3-week intervals. Emergence and development of plants increased with temperature. April through August plantings yielded 10-to 20-fold as much total fresh weight as March and September plantings. After planting, rhizome production normally began in 3 to 6 weeks and seed production in 6 to 9 weeks. From the April through August plantings, rhizomes accounted for averages of 13, 25, and 40% of the total fresh weight of plants 6, 9, and 12 weeks after planting, respectively. This compared, respectively, with 16, 9, and 6% for roots and 70, 66, and 54% for shoots. Seedlings emerging in March produced rhizomes in early June and viable seed in late June. Seedlings emerging as late as September produced rhizomes and some viable seed before killing frosts in November.