Abstract: The potential of Colletotrichum dematium f.sp. epilobii (ATCC 20981) to control fireweed (Epilobium angustifolium) was investigated. Under controlled environment conditions, plant age, inoculum density, length of the dew period, and temperature during the dew period affected the efficacy of C. dematium f.sp. epilobii. Seedlings sprayed with 1 × 109 conidia/m2 sustained the most damage. Susceptibility decreased with increasing plant age, and 10-wk-old plants were slightly affected by the fungus. Satisfactory levels of control were achieved when the dew period was >20 h and temperature during the dew period was 30 C. Control of fireweed increased when the C. dematium f.sp. epilobii conidia were suspended in a 25% v/v canola oil/water emulsion. Using this formulation, control of 4-wk-old seedlings was obtained with a 10-fold reduction in inoculum concentration (1 × 108 conidia/m2), the required dew period was reduced to 12 h, and the effect of the temperature during the dew period was minimized. In the field, C. dematium f.sp. epilobii alone or when amended with an oil emulsion failed to control fireweed growth. When the oil formulation of C. dematium f.sp. epilobii was tank mixed with a low rate of glyphosate, high levels of control were consistently achieved. Growth reduction achieved with this formulation was more than additive, suggesting a synergistic interaction. The effectiveness of the formulated conidial suspension of C. dematium f.sp. epilobii decreased with plant maturity, and 15-wk-old plants were not controlled. C. dematium f.sp. epilobii alone has limited potential as a candidate bioherbicide, but when formulated in an oil/water emulsion and combined with low rates of glyphosate, suppression of fireweed can be attained in the field.
Nomenclature: Glyphosate; fireweed, Epilobium angustifolium L. #3 CNAAN.
Additional index words: Bioherbicide, biological weed control, mycoherbicide.
Abbreviations: PDA, potato dextrose agar; SNK, Student-Newman-Keuls Multiple Range test.