Uptake, translocation and phytotoxicity of imazapyr and glyphosate in Imperata cylindrica (L.) Raeuschel: effect of herbicide concentration, position of deposit and two methods of direct contact application

Summary: The activity of imazapyr and glyphosate against Imperata cylindrica was studied in field and glasshouse experiments using two methods of direct contact application; a rope‐wick wiper and a cloth soaked in herbicide solution. The effect of concentration and position of application on herbicide uptake and translocation was also measured. At the lowest dose of imazapyr (5 mg acid equivalent (a.e.) per plant), phytotoxicity was greater from applications by a rope‐wick wiper than by a cloth. However, when the dose of imazapyr was increased, the cloth applicator was more effective than the rope‐wick wiper. At all doses of glyphosate, rope‐wick application was more effective than wiping with a cloth. Herbicide performance in the glasshouse was similar to that in the field. Radiotracer studies showed that increasing the concentration of imazapyr, while keeping herbicide dose constant, decreased uptake and translocation of radiolabel. In contrast, the rate of uptake of 14C‐glyphosate increased with increasing herbicide concentration. Position of application did not significantly affect the amount of uptake and translocation of radiolabel to the rhizomes. It is concluded that rope‐wick wipers are more effective than wiping with a cloth for applying imazapyr and glyphosate to I. cylindrica, provided that the concentration of imazapyr does not exceed 10 g a.e. l−1.