Kochia is a troublesome weed throughout the western United States. Although glyphosate effectively controls kochia, poor control was observed in several no-till fields in Kansas. The objectives of this research were to evaluate kochia populations response to glyphosate and examine the mechanism that causes differential response to glyphosate. Glyphosate was applied at 0, 54, 109, 218, 435, 870, 1305, 1740, 3480, and 5220 g ae ha⁻¹ on 10 kochia populations. In general, kochia populations differed in their response to glyphosate. At 21 d after treatment, injury from glyphosate applied at 870 g ha⁻¹ range from 4 to 91%. In addition, glyphosate rate required to cause 50% visible injury (GR₅₀) ranged from 470 to 2149 g ha⁻¹. Differences in glyphosate absorption and translocation and kochia mineral content were not sufficient to explain differential kochia response to glyphosate.

Nomenclature: Glyphosate; kochia, Kochia scoparia (L.) Schrad.