The Influence of Glyphosate on Bud Dormancy in Leafy Spurge (Euphorbia esula)

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Abstract
Glyphosate [N-(phosphonomethyl)glycine] was applied in the spring and fall to leafy spurge (Euphorbia esulaL. # EPHES) in the field at rates of 0.14 to 4.48 kg ai/ha. Fall applications of glyphosate at rates of 0.56 to 4.48 kg/ha stimulated axillary branching and caused an increase in the number of stems/m2by the end of the following summer in a dense population. This was a result of shoot growth from buds on the crown region of the root system. The absorption and translocation of14C-glyphosate applied to leaves of mature leafy spurge plants were evaluated at prebloom, full-bloom, and senescence phenological stages. Approximately 81% of the14C-glyphosate applied to the leaves of senescing plants was absorbed. There was a decrease in the proportion of14C translocated out of the treated leaf when applications were made after full bloom. Translocation of14C to the treated stem, nontreated stems, root crown, and roots did not differ with phenological stage in 1983. Translocation and concentration of14C in most plant parts in 1985 differed with phenological stage. Translocation to the crown buds as a percentage of the14C absorbed was highest at the senescence stage. At senescence and before soil freezing, leafy spurge crown buds demonstrate transient but active elongation toward the soil surface. This active development may account for the enhanced translocation of14C into the crown buds.