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Sciegienka, J. K., Keren, E. N. and Menalled, F. D. 2011. Impact of root fragment dimension, weight, burial depth, and water regime on Cirsium arvense emergence and growth. Can. J. Plant Sci. 91: 1027–1036. Cirsium arvense is an aggressive, introduced, perennial invasive weed that flourishes in a wide variety of environments including conventional and organic agricultural systems as well as disturbed non-crop habitats. Even though much research has been conducted on the chemical, biological, and cultural management of C. arvense, less information is available on how pre-emergence factors affect its reproductive biology and growth. This research assessed the combined impact of root fragment size, root fragment biomass, burial depth, and water regime (a proxy of water availability) on C. arvenseemergence and growth in fallow conditions. In field experiments, root burial depth was the most important factor determining C. arvenseemergence and growth, with roots at the 10-cm depth having the greatest average emergence (51.2±2.0% in 2007 and 43.5±7.2% in 2008; mean±SEM) compared to roots at the 2 cm (8.9±7.4% in 2007 and 38.1±8.3% in 2008) or 20 cm (12.8±4.0% in 2007 and 17.6±2.7% in 2008) depth. In greenhouse experiments, water regime was the overriding variable determining C. arvense emergence as well as above-ground and below-ground biomass. These results could improve decision-aid models and enhance the efficacy of site-specific C. arvense management practices.

We investigated the single and combined effects of two biological control agents, the stem-mining weevilHadroplontus lituraand the pathogenPseudomonas syringaepv.tagetis, with a herbicide (reduced or full application of glyphosate: 0.63 kg ae ha−1, or 3.78 kg ae ha−1, respectively) on the growth of Canada thistle,Cirsium arvense. We hypothesized that first, although each control method would have a negative effect on Canada thistle shoot biomass, root biomass, and shoot number, the integration of more than one control method would have greater impact than individual control methods. Second, we hypothesized that the order in which control methods are applied affects the outcome of the management program, with a pathogen application following weevil infestation being more effective than one prior to it. Although control methods impacted Canada thistle growth (P < 0.001, expect for a nonsignificant impact of glyphosate on shoot number), the combined effect of the three control methods behaved, generally, in an additive manner. A marginal interaction between the pathogen and the herbicide (P = 0.052) indicated a slight antagonistic interaction between these control methods. An interaction between the two biological control agents tested (P < 0.001) indicated that application of a pathogen prior to the release of weevil larvae could be more deleterious to Canada thistle than a late application. The observed, mostly additive, relationship between biological control agents and herbicides implies that integrating control methods rather than using a single approach could lead to greater Canada thistle control.