Variations in the resistance of Stellaria media to mecoprop due to biotype, application method and 1-aminobenzotriazole

An investigation was made into the resistance of some biotypes of Stellaria media to mecoprop. Comparison of the sensitivity of five biotypes to foliar applications of mecoprop salt confirmed the presence of resistant and sensitive types and one of intermediate sensitivity. Applications of mecoprop through the roots of plants growing in nutrient culture were also more active on biotypes sensitive to foliar mecoprop, although the differences were less marked than they were with foliar treatments. Thus, possible differ ences in retention, uptake and translocation do not seem to be important causes of resistance. Consequently, it appears that resistance is associated with detoxification of mecoprop at the site of action. In two further experiments the cytochrome P450 mixed function oxidase inhibitor, 1-aminobenzotdazole, had only a small effect on the susceptibility of resistant S. media plants to mecoprop. The importance of these data in the elucidation of the mechanism of resistance is discussed.