Summer weeds carry disease, impede crop sowing and utilise stored soil moisture or nutrients that may otherwise be available to the subsequent crop (Cameron & Storrie, 2014). Identifying summer weeds informs growers of the major weed issues in different agronomic regions and provides direction for future research on emerging weed species. A GRDC funded project has surveyed roadside summer weeds in the Western Australian (WA) wheatbelt in the summer of 2014/2015, 2015/2016, and 2016/2017. This project aimed to determine the prevalence and density of emerging summer weeds, and highlight the variation between years.
A survey was conducted over all main roads within the WA wheatbelt during February to April 2015, 2016 and 2017. In 2015, a total of 244 sites were selected approximately every 10 km, where weeds were visible on the roadside. In 2016 and 2017, 138 and 238 sites were revisited. At each site, weed species were identified along a 20 m long transect. Weed density (seed head or tillers for grass weeds and plant numbers for broadleaf weeds) was determined by visual assessment. Density for each species was recorded as low (0-10 plants/m2), medium (11-50 plants/m2) or high (>50 plants/m2). Photos were taken to allow later identification of ambiguous species.
The survey identified a total of 144 separate species (or genera where species were grouped at the genus level) at 244 sites evenly distributed throughout the wheatbelt. A total of 76, 72 and 129 species were identified in 2015, 2016 and 2016. However, only 58 weeds were found at greater than 1% of sites and only 19 weeds were found at greater than 10% of sites.