Evaluation of the "fall rosette" procedure for perennial sowthistle control in fallow

Abstract

Field experiments conducted near Grande Prairie, Alberta, compared the effectiveness of the fall rosette procedure to other procedures used in a year of fallow for the control of perennial sowthistle (Sonchus arvensis L.). The fall rosette procedure, which consisted of discontinuing normal cultivation in late July, allowing the perennial sowthistle plants to grow for 6 wk and then applying glyphosate plus dicamba at 0.6 + 0.6 kg ha−1 plus Agral 90 at 0.5% vol/vol of spray volume, reduced shoot density by 84, 90 and 96% approximately 1 yr after imposition in 1992, 1993 and 1994, respectively. By comparison, the bud stage procedure, which consisted of allowing plants to grow to the bud stage in the spring/early summer, applying the same herbicide treatment and conducting tillage for the rest of the year, reduced shoot densities by 58, 86 and 85% when imposed in the same years, respectively. The fall rosette procedure was also more effective than frequent tillage throughout the growing season without herbicide, or than chemfallow (glyphosate plus dicamba applied in early July and again in early September, with or without late fall tillage) in reducing perennial sowthistle shoot density. Mowing, whenever the perennial sowthistle reached 8–10 cm in height, did not reduce shoot density. Key words: Fall rosette, bud stage, Sonchus arvensis L., tillage, mowing, chemfallow