NGN Summer weeds fleabane and sowthistle management demonstrations for the Victorian Mallee

Fleabane and sowthistle are difficult to control summer weeds impacting growers in the Victorian Mallee. Seed production of both fleabane and sowthistle is prolific, can spread by wind, and can produce several generations through multiple germination events each year. These weed species are particularly problematic to manage in summer fallows where they reduce stored water availability to subsequent crops, and a reliance on herbicides to manage these weeds has led to development of resistance to Groups 2 (sulfonylurea) and 9 (glyphosate) herbicides, and additionally Group 22 (paraquat) in fleabane and Group 4 (2,4-D) in sowthistle. At NGN forums held at Lake Cullulleraine, Natya, Pyramid Hill and Manangatang in August 2024 hard to control weeds including fleabane and sowthistle were identified as growers’ primary constraint. The forum participants discussed the economics of summer chemical control options, with effective options such as the application of ‘double knocks’ with labour requirements costing around $50/ha, which is considered generally prohibitive in these low rainfall areas. GRDC has invested in research to understand the biology and ecology of these weeds and inform management tactics to ultimately reduce seed set. These strategies have been evaluated and compiled in the ‘Integrated Weed Management Manual’. Additionally, GRDC has invested in the recently released ‘Summer Weed Tool’ application that assists growers to consider the benefits of weed control for yield, prospective profit, and water retention. Victorian Mallee grain growers are experiencing limited effectiveness of current weed control strategies and now seek to explore new tools and practices to manage fleabane and sowthistle and take pressure off their summer spray program.