A new strain of the fungus Plectosporium tabacinum was isolated from naturally-infected false cleavers plants and evaluated as a bioherbicide for the control of both herbicide-resistant and herbicide-susceptible false cleavers in canola. Plectosporium tabacinum was nonpathogenic to both Argentine canola and Polish canola and to both herbicide-tolerant and conventional cultivars. Plectosporium tabacinum killed false cleavers seedlings when applied at a concentration of 1 × 107 conidia ml−1 and provided with 16 h dew. The efficacy of P. tabacinum on herbicide-resistant false cleavers was identical to that on herbicide-susceptible false cleavers. Catchweed bedstraw was also highly susceptible to P. tabacinum. Further host-range tests on 34 plant species in 26 genera and 12 families demonstrated that P. tabacinum is sufficiently host specific for false cleavers control in western Canada. This fungus may provide a novel approach for managing herbicide-resistant false cleavers.
Nomenclature: Plectosporium tabacinum (van Beyma) M. E. Palm, W. Gams et Nirenberg; Argentine canola, Brassica napus L.; catchweed bedstraw, Galium aparine L. GALAP; false cleavers, Galium spurium L. GALSP; Polish canola, Brassica rapa L.