Evaluation of Fusarium avenaceum and other fungi for potential as biological control agents of invasive Rubus species in British Columbia

Fungi were Isolated from naturally Infected Rubus srrigosus. R. parviflorus. and R. specrabi/is plants in an attempt to identify biological control agents for these invaSIve species in reforestation sites. Three endemic fungi. Fusarium avenaceum, ColIelOlrlchum demarium. and a Phomopsis sp.. were selected for further study after they were found to induce >50% leaf area necrosis when inoculated onto detached Rubus leaves using in vitro pathogenicity tests. However. when inoculum was applied to intact Rubus plants under shadehouse conditions. significant foliar necrosis was not observed. Inoculum production methods. amendment of inocula with adjuvants. and application of low doses of glyphosate were investigated for their effects on patho genicity. Foliar infection was increased significantly when inoculum of F. avenaceum was grown on a rice-grain substrate an~ applied in combination with an organosilicone surfactant (0.4% Silwet L-77®) to R. strigosus and R. parviflorus plants. Extracuon and analysis of infested nce filtrates for metabolite production showed that a single toxin, moniliformin, was present at levels of 3300 ppm. Pathogenicity of the other two fungi was not enhanced under any conditions assayed. The potential for further development of F. avenaceum as a biological control agent of weedy Rubus species is discussed.