Changes in plant species composition after flupropanate application for nassella tussock control, in Canterbury hill-country pastures

Field trials were conducted in hill-country pastures in Canterbury, New Zealand, to evaluate the herbicide flupropanate on nassella tussock (Nassella trichotoma) and associated pasture species. Pastures at three sites (Banks Peninsula, Spotswood and Greta Valley) and sprayed with flupropanate at 0, 0.75, 1.49 or 2.98 kg a.i./ha in March 2012. Pasture species composition was assessed in November/December 2011 (before treatment) and in November 2012. Pasture damage was assessed 3.5, 8.5 and 12 months after treatment (MAT). Cover of pasture species was reduced by 43%, 89% and 12% at 8.5 MAT at 1.49 kg a.i./ha, compared to untreated, for the three sites, respectively. Bare ground increased 3-fold to 51%, and 2.5-fold to 79% at Banks Peninsula and Spotswood but did not increase at Greta Valley. Cover of Asteraceae weeds, mainly thistles, increased at all three sites. Results indicate that flupropanate was severely damaging to some important pasture species at some sites.