Chemical control of ambrosia Artemisiifolia on non-crop areas: are there alternatives to glyphosate?

We compared glyphosate, glufosinate and metsulfuron-methyl to control Ambrosia artemisiifolia under non-crop conditions. A laboratory study showed that A. artemisiifolia is an easy-to-wet species and that glufosinate and glyphosate are quickly absorbed by its leaves (nearly 100% in 24 h). Metsulfuron-methyl absorption was slower (about 50% in 24 h) but was strongly promoted by terpenic alcohol and esterified rapeseed oil. In the greenhouse, all three herbicides were efficacious against A. artemisiifolia, with ED50s of <23, 23 and 0.8 g ha(-1) for glufosinate, glyphosate and metsulfuron-methyl, respectively. These results were confirmed on a non-crop area for glufosinate and glyphosate, which at half the registered dose reached high efficacies at both the 4 to 6-node and flowering stages of A. artemisiifolia. By contrast, metsulfuron-methyl showed no efficacy. However, after treatment at the 4- to 6-node stage, new emergence of A. artemisiifolia led to the presence of vigorous plants that bore numerous flowers and produced high levels of pollen. After treatment at the flowering stage, flower production by A. artemisiifolia was not significantly affected, but achene weight was decreased by 60 to 70% and seed viability was only 8 to 13% for the treated plants, as compared to 85% for the control. No significant difference was observed between the two herbicides and between the doses. It is concluded that glufosinate can be an alternative to glyphosate for the chemical control of A. artemisiifolia on non-crop areas. However, with both herbicides, it is difficult to attain the two objectives of reducing seed production and pollen production by means of only one treatment.