Beschreibung:
<jats:p><jats:italic>Cirsium arvense</jats:italic> (Canada thistle) is a perennial weed that causes significant economic losses in agriculture. An extensive rhizomatous root system makes <jats:italic>C. arvense</jats:italic> difficult to manage, particularly in agricultural systems that use tillage as a primary management tool. There is a need for the development of integrated weed management toolsets that include <jats:italic>C. arvense</jats:italic> biological controls. <jats:italic>Puccinia punctiformis</jats:italic> (thistle rust) is an autoecious fungal pathogen that systemically infects <jats:italic>C. arvense</jats:italic>, with the potential to reduce host vigor over time. The goal of this study was to integrate the <jats:italic>P. punctiformis</jats:italic> biocontrol with a simulated annual cropping sequence in a greenhouse environment and evaluate <jats:italic>C. arvense’s</jats:italic> above-and belowground biomass production, and its competitive ability. Repeated <jats:italic>P. punctiformis</jats:italic> inoculations produced systemically infected <jats:italic>C. arvense</jats:italic> stems in greenhouse pots over time. <jats:italic>Cirsium arvense</jats:italic> that was inoculated with <jats:italic>P. punctiformis</jats:italic> had 1.6 grams/pot (<jats:italic>p = 0.0019</jats:italic>) less aboveground biomass and 5.6 grams/pot (<jats:italic>p&lt; 0.001)</jats:italic> less belowground biomass, compared to the non-inoculated (control). <jats:italic>Puccinia punctiformis</jats:italic> and crop competition interacted additively to lower aboveground (p&lt;0.001) and belowground (p&lt;0.001) <jats:italic>C. arvense</jats:italic> biomass more than individual use of either the biocontrol or competition alone. The aboveground competition intensity of <jats:italic>C. arvense</jats:italic> in a mixed crop sequence, relative to non-inoculated <jats:italic>C. arvense</jats:italic> grown in a monoculture, was moderately impacted by the <jats:italic>P. punctiformis</jats:italic> biocontrol (<jats:italic>p = 0.0987</jats:italic>). These results indicate that systemic infection can reduce biomass production and the competitive ability of <jats:italic>C. arvense</jats:italic>. Overall, <jats:italic>P. punctiformis</jats:italic> can be integrated into competitive annual cropping sequences with the potential to reduce <jats:italic>C. arvense</jats:italic> vigor over time.</jats:p>