Efficacy of glyphosate, alternative post-emergence herbicides and tillage for control of Cynodon dactylon

Abstract

Cynodon dactylon (L.) Pers (cynodon) is a major weed in the South African sugarcane industry. Current recommendations involve repeated application of glyphosate for prolonged control. This paper describes three trials of a study to identify alternative treatments. Trial 1 screened seven non-glypho-sate candidate chemical treatments, trial 2 investigated the effect of tillage prior to herbicide application, and trial 3 compared the best candidate product with glyphosate for phytotoxicity to sugarcane. In trial 1, fluazifop-butyl, imazapyr and glyphosate all provided >95% control for up to 19 weeks after treatment (WAT). In trial 2, treatment of cynodon without prior tillage, with glyphosate and imazapyr provided >90% control up to 20 WAT. However, in cynodon subjected initially to tillage, glyphosate efficacy was reduced to 60% at 12 WAT, whereas imazapyr provided 90% control for up to 20 WAT. Tillage plus a tank mixture of glyphosate plus imazapyr provided significantly higher control than either component when applied separately. Imazapyr suppressed pioneer species to a greater extent than glyphosate and, in trial 3, was not more phytotoxic than glyphosate under the tested conditions. Conclusions are that a) imazapyr is a promising candidate for cynodon control, with further work required to provide recommendations; and b) minimum tillage using glyphosate for sugarcane eradication is preferred to ploughing out stools in cynodon-infested fields.