Annual sowthistle (Sonchus oleraceus L.) is a broadleaf weed that is increasing in prevalence in the northern cropping regions of Australia. Being a member of Asteraceae family, this weed possesses many biological attributes needed to thrive in varying environments and under differing weed management pressures. Interference of this weed in a wheat (Triticum aestivum L.) crop was examined through field studies in 2016 and 2017. Different densities of S. oleraceus were evaluated for their potential to cause yield loss in wheat: 0.0 (weed-free), low (9 to 15 plants m^–2), medium (29 to 38 plants m^–2), and high (62 to 63 plants m^–2). Based on the exponential decay model, 43 and 52 plants m^–2 caused a yield reduction of 50% in 2016 and 2017, respectively. Yield components such as panicles per square meter and grains per panicle were affected by weed density. At the high weed infestation level, S. oleraceus produced a maximum of 182,940 and 192,657 seeds m^–2 in 2016 and 2017, respectively. Sonchus oleraceus exhibited poor seed retention at harvest, as more than 95% of seeds were blown away by wind. Adverse effects on crop, high seed production, and wind-blown dispersal may lead to an increased prevalence of this weed in the absence of an integrated weed management strategy utilizing both herbicides and nonchemical options.