Field and controlled environment experiments were performed to assess the preemergence activity of the fungal pathogen, Phomopsis convolvulus Ormeno to control Convolvulus arvensis L. (field bindweed). A granular barley formulation of the fungal inoculum applied onto the field soil surface resulted in dramatic aboveground biomass reductions of both C. arvensis seedlings (94--100%) and regrowth from established plants (53--98%). Under field conditions, surface applications of the granular formulation resulted in greater biomass reductions (93--100%) compared with soil incorporation of the granules (31--97%). Rate of soil applied granules of P. convolvulus did not affect the level of weed control and 90--100% C. arvensis biomass reductions were obtained for all rates used (30 g, 20 g, and 10 g 0.25m--2 plot). The use of two different planting substrates in controlled environment studies led to major differences in C. arvensis disease development. With an inoculum application on the day of sowing, 81% mortality was obtained for seedlings grown in a sandy loam field sod compared with 50% of seedlings grown in a prepared peat moss medium. The susceptibility of C. arvensis biotypes from various geographic locations to P. convolvulus was similar following post-emergence, foliar inoculum applications. Significant above-ground (65--100%) and new root growth (56--72%) biomass reductions of established plants were obtained for two selected biotypes (Greece, USA-Montana) subjected to a preemergence granular inoculum application. In the presence of spring wheat (Triticum aestivum L.), field efficacy of P. convolvulus was enhanced and aboveground biomass of inoculated C. arvensis plants was reduced by 98% compared with inoculated C. arvensis plants grown in pure stand.

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