Although stand-alone and integrated management techniques have been cited as viable approaches to managing Canada thistle [Cirsium arvense(L.) Scop.], it continues to impact annual cropping and perennial systems worldwide. We conducted meta-analyses assessing effectiveness of management techniques and herbicide mechanism of action groups for controllingC. arvenseusing 55 studies conducted in annual cropping systems and 45 studies in perennial systems. Herbicide was the most studied technique in both types of systems and was effective at reducingC. arvense. However, integrated multitactic techniques, with or without herbicides, were more effective than sole reliance on herbicides for long-term control in both annual cropping and perennial systems. A variety of management techniques such as biocontrol, crop diversification, mowing, and soil disturbance provided control similar to that of herbicide. Our results suggest that many management techniques aimed at reducingC. arvensecan also improve crop yield or abundance of desired plants. This study highlights the need to devote more research to nonchemical and integrated management approaches forC. arvensecontrol.

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Field bindweed (Convolvulus arvensisL.) is a persistent, perennial weed species that infests a variety of temperate habitats around the globe. To evaluate the efficacy of general management approaches and impacts on crop yield and to identify research gaps, we conducted a series of meta-analyses using published studies focusing onC. arvensismanagement in annual cropping and perennial systems. Our analysis of 48 articles (560 data points) conducted in annual systems indicated that 95% of data points measured efficacy over short time frames (within 2 yr of treatment). Furthermore, only 27% of data points reported impacts ofC. arvensismanagement on crop yield. In annual systems, herbicide control dominated the literature (~80% of data points) and was an effective management technique up to 2 yr posttreatment. Integrated management, with or without herbicides, and three nonchemical techniques were similarly effective as herbicide at reducingC. arvensisup to 2 yr posttreatment. In addition, integrated approaches, with or without herbicides, and two nonchemical techniques had positive effects on crop yield. There were few differences among herbicide mechanism of action groups onC. arvensisabundance in annual systems. There were only nine articles (28 data points) concerningC. arvensismanagement in perennial systems (e.g., pasture, rangeland, lawn), indicating more research effort has been directed toward annual systems. In perennial systems, biocontrol, herbicide, and non-herbicide integrated management techniques were equally effective at reducingC. arvensis, while competition and grazing were not effective. Overall, our results demonstrate that while chemical control ofC. arvensisis generally effective and well studied, integrated and nonchemical control practices can perform equally well. We also documented the need for improved monitoring of the efficacy of management practices over longer time frames and including effects on desired vegetation to develop sustainable weed management programs.

In winter wheat systems in the Northern Great Plains of the United States, Bromus tectorum and wheat streak mosaic virus (WSMV) commonly co-occur. While independent effects of these pests on wheat yields have been well documented, to our knowledge, no study has investigated whether WSMV modifies interactions between wheat and B. tectorum. Furthermore, the impact that environmental stressors such as nutrient availability have on these interactions has not been addressed. We conducted a randomised split-plot field study over 2 years to investigate the effects of WSMV and nitrate (N) availability on winter wheat suppression of Bromus tectorum. The study included four N treatments (10-19, 20-31, 31-84, and 85-207 kg ha À1 ) and two WSMV treatments (mechanically inoculated or control). Increasing soil N increased the susceptibility of wheat to WSMV infec-tion. In 2009, wheat in the lowest and highest N levels had 24% and 65% of plants infected respectively. However, regression analysis indicated that interactive effects of wheat competition, N and WSMV did not play a consistent role in B. tectorum growth. Specifically, the effect of both wheat density and distance from row on B. tectorum biomass remained constant across inoculation treatments, suggesting that wheat inoculated with WSMV suppressed B. tectorum as effectively as healthy wheat. Furthermore, wheat had a greater impact on B. tectorum growth in higher N environments, even though incidence of WSMV infection in wheat was highest. Overall, our results suggest that WSMV infection may not change the ability of wheat to suppress B. tectorum.