Yellow bristle grass presence in two key New Zealand dairy regions: trends in pasture infestations and roadside spread

摘要

Yellow bristle grass (Setaria pumila (Poir.) Roem. & Schult.) is a summer-active C4 annual species prevalent in dairy pastures in the upper North Island of New Zealand. It provides poor quality forage and plants may be avoided by grazing livestock once seedheads emerge. There are also concerns that the bristles can penetrate the mouth parts of grazing livestock and cause harm. Two surveys were undertaken to monitor its spread; the first monitored trends in bristle grass ground cover in an infested dairy region and the second monitored its spread along roadsides in a region recently invaded. In the first instance, 39 dairy pastures were monitored once each summer in the Waikato region over seven years (2008-2014). Yellow bristle grass presence remained below 12% of total ground cover, although there were increases in its cover in the years following the 2008 drought. Monthly assessments from January to April of seedhead presence before and after grazing in three of the surveyed pastures showed thatYBG was grazed throughout the season, regardless of seedhead presence. In the second survey, rural roadsides in the Taranaki region were monitored once annually in February for bristle grass presence over two years (2013-2014). In February 2013, yellow bristle grass was prevalent along the roadsides that were major access routes within the region, with some infestations noted on less frequently used (minor) roads, particularly where minor roads intersected with the major roads. In the following summer (February 2014), the distribution was similar, with some outlying patches no longer present (most likely due to local council control measures), with some spread along roads near major towns.