Investigating herbicide tolerances of native plants to improve urban restoration

Herbicides are a vital tool to reducing weed competition during the establishment phase of revegetation plantings. However, there is limited information on herbicide tolerances of native species, hindering the ability to develop effective weed-management plans. In a pilot study, tolerances of five New Zealand native species (Coprosma propinqua, Griselinia littoralis, Hoheria angustifolia, Prumnopitys taxifolia, and Cyperus ustulatus) were tested against the herbicides clopyralid, haloxyfop-P-methyl, triclopyr, glufosinate-ammonium and glyphosate at label rates, and to a dilute glyphosate treatment used to simulate drift from spraying around native plants. Treatments were sprayed directly onto plants, with survival and growth over four months compared to a control group. Clopyralid caused significant damage to H. angustifolia and G. littoralis, but increased growth in Cyperus ustulatus. Haloxyfop-P-methyl did not damage any species. While glyphosate and glufosinate-ammonium at label rates caused significant mortality, a low dose of glyphosate did not damage any species except Coprosma propinqua. Triclopyr also caused significant mortality or damage even in non-dicotyledonous plants, possibly due to small plant sizes. These results identify broader than expected susceptibility to triclopyr and clopyralid, suggesting additional caution with these herbicides may be required. The findings from this study also indicate that spraying glyphosate carefully around these species is unlikely to cause harm, except to Coprosma propinqua.