Experiments were conducted to study absorption, translocation, and activity of clopyralid and tribenuron in perennial sowthistle. Absorption and translocation were compared in perennial sowthistle at the rosette and bud stage over a period of 9 d. Both 14C-clopyralid and tribenuron were absorbed slowly by perennial sowthistle leaves with 60 and 30% absorption, respectively, 216 h after application. Limited movement of the absorbed 14C was observed for both herbicides with less than 28% of either herbicide exported from the treated leaf. Primary movement of 14C-herbicide within the plant was acropetal; however, no more than 18% of either herbicide was recovered in the upper shoot or buds. After 216 h, 4.4% of the applied 14C-clopyralid and 2.5% of the applied 14C-tribenuron were recovered in the roots and secondary shoots of plants at the rosette stage. Application of either herbicide to perennial sowthistle resulted in a decrease in net carbon assimilation and leaf conductance. Transpiration was reduced in rosette stage plants by both herbicides; however, transpiration in plants at the bud stage was not reduced until 216 h after treatment. Plants treated with tribenuron had lower net carbon assimilation, leaf conductance, and transpiration rates than plants treated with clopyralid. Application of clopyralid at 150 and 300 g ha-1 resulted in visual injury ratings of 65 and 95%, respectively. Tribenuron applied at 10 and 20 g ha-1 gave similar results. Dry weight accumulation was reduced at all application rates compared to untreated plants. Limited absorption and translocation along with high herbicidal activity suggests that small amounts of either herbicide are sufficient to inhibit perennial sowthistle growth.

A mixture of 2,4-D with either thiameturon, DPX-L5300, or DPX-R9674 controlled common chickweed in winter wheat better than 2,4-D alone. None of these herbicides affected wheat height, lodging, or yield. Similarly, no significant differences in wheat height or lodging occurred among seeding rates. Wheat sown near South Charleston, OH, at a seeding rate of 67 kg/ha yielded significantly less than that sown at 100 or 134 kg/ha; however, there was no difference in wheat yield among seedling rates at a second location near Columbus, OH.

A biotype of kochia resistant to chlorsulfuron has been isolated from a Kansas wheat field that had been treated with chlorsulfuron for five consecutive years. In greenhouse tests, the biotype also was resistant to both preemergence and postemergence herbicides with the same mode of action including imazapyr, CGA-131036, the methyl ester of metsulfuron, DPX-M6316, DPX-L5300, and the methyl ester of sulfometuron. The degree of cross resistance varied among the herbicides tested. Herbicides with different modes of action, including atrazine, bromoxynil, MCPA, and diuron, effectively controlled the resistant biotype in the greenhouse.