Effect of soil incorporation and dose on control of field bindweed (Convolvulus arvensis) with the preemergence bioherbicide Phomopsis convolvulus

The preemergence efficacy of soil surface applications of a Phomopsis convolvulus granular formulation to control field bindweed seedlings was compared with its efficacy when inoculum granules were incorporated in soil. In addition, the effect of different doses of soil-applied granules was also determined. Under controlled environment conditions, incorporation of the fungal granules resulted in aboveground biomass reductions between 88 and 96%, with no significant differences observed between incorporation depths of 1.5 and 3 cm. Granule applications on the soil surface were less effective, reducing aboveground biomass 40 to 83%. In a parallel field experiment conducted over two growing seasons, however, surface applications of inoculum granules resulted in greater weed control compared with soil incorporation of the granules. In spring and summer trials conducted in 1996, surface applications resulted in a 93 and 100% aboveground biomass reduction, respectively, whereas incorporated granules reduced biomass 62 and 97%. Similar trends were observed in 1997. Different soil-applied doses of P. convolvulus did not affect the level of weed control under both controlled environment and field conditions. In 1995 and 1996 field trials, all rates used (30, 20, and 10 g 0.25m(-2) plot) resulted in substantial (30 to 100%) field bindweed aboveground biomass reductions. Findings in this study indicate that under field conditions, preemergence applications of the bioherbicide P. convolvulus on the soil surface provide effective control of field bindweed.