A meta-analysis of field bindweed (Convolvulus arvensis L.) and Canada thistle (Cirsium arvense L.) management in organic agricultural systems

Organic farming has become a major agricultural and economic sector, and weed management is one of the primary challenges facing the industry. Of particular concern are rhizomatous perennial weeds such as field bindweed (Convolvulus arvensis L.) and Canada thistle [Cirsium arvense (L.) Scop.] which are highly competitive and not easily controlled in organic systems. We conducted meta-analyses of the existing literature to 1) identify promising management approaches for these weeds in the absence of synthetic herbicides and 2) determine which aspects of field bindweed and Canada thistle management warrant further study. Mechanical control (i.e. plowing, cultivation, hoeing) was the most studied management category in annual cropping systems, accounting for 40% of data extracted, but did not outperform most of the other management actions overall, possibly due to the variability in specific methodology (i.e. timing, frequency, depth, implement). In annual systems, integrated management, or the combination of two or more control methods, emerged as the management technique that caused the greatest decrease in abundance and survival for field bindweed. We identified several additional management techniques that decreased field bindweed and/or Canada thistle in both annual and perennial systems including biocontrol, mowing, grazing, crop diversification, solarization, shading, flaming, and crop competition. However, organic producers continue to struggle with these species. This discrepancy may originate from the fact that most of the studies we evaluated reported impacts over short time spans, with 53% being conducted for a period of one to two years, and only 9% conducted for five or more years. Further, only 16% of field bindweed and 26% of Canada thistle studies reported measures of variability. Longer-term research focused on sustainable perennial weed management systems is needed in addition to research about short-term interventions.