Distribution, Competition, and Phenology of Hemp Dogbane (Apocynum cannabinum) in Nebraska

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Abstract
All land uses in eastern and southeastern Nebraska were infested to some extent with hemp dogbane (Apocynum cannabinumL.). The highest infestations were observed in oats (Avena sativaL.) and soybeans [Glycine max(L.) Merr.] and the lowest infestations were in alfalfa (Medicago sativaL.), pastures, and winter wheat (Triticum aestivumL.). Yield reductions from hemp dogbane infestations ranged from 0 to 10% in corn (Zea maysL.), 28 to 41% in soybeans, and 37 to 45% in sorghum [Sorghum bicolor(L.) Moench]. Emergence of hemp dogbane from crown roots occurred when the soil temperature was 17 to 19 C, during April in 1977 and 1978. Plants attained the bud stage within 4 to 7 weeks after emergence. Early flower, full bloom, and pod initiation occurred subsequently at about 1 week intervals. Seeds produced were first viable 10 weeks after full bloom. Root activity or regenerative capacity as measured by length and number of new shoots and roots produced at monthly intervals in the germinator showed a cyclic pattern. The highest activity occurred in the spring and late fall and lowest activity in summer and early fall. Protein levels in the roots ranged from 7 to 9% in the fall and spring to 4 to 5% during the summer. Percentage total nonstructural carbohydrates (TNC) ranged from 20 to 31% in lateral roots and 32 to 53% in crown roots, but there was not a consistent cyclic pattern of percentage TNC during the growing season.