FIELD SURVIVAL OF PHOMA-PROBOSCIS AND SYNERGISM WITH HERBICIDES FOR CONTROL OF FIELD BINDWEED

Small plot field tests were conducted in Washington County, AR, and Phillips County, CO, to determine the efficacy of Phoma proboscis conidia in control of field bindweed (Convolvulus arvensis) under various temperature and moisture conditions during 1990-1993. Treatments included combinations of conidia with a formulation of 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-(2-methyl-4-chlorophenoxy)propionic acid (MCPP) used at a sublethal dose of 18 g a.i./ha, the surfactants Activate 9-0 or Activate Plus, corn oil, or sodium alginate. Dew periods of less than 6 hr or temperatures less than 10 C or approaching 32 C were inhibitory to the infection process required for field bindweed control. A rate of 10(7) conidia per milliliter in combination with a sublethal dose of 2,4-D and MCPP increased disease to the level achieved with 10(8) conidia per milliliter and controlled field bindweed. The 10(8) conidia per milliliter rate in combination with a sublethal dose of 2,4-D and MCPP killed mature field bindweed tissue during the later part of the growing season (31 July and 4 September 1992) when dew periods were adequate (8-10 hr). Air-dried conidia were as effective as fresh conidia in causing disease. Nylon membranes and field bindweed stems infested with P. proboscis were buried at 1-, 10-, and 20-cm depths at the Arkansas field site and recovered monthly during the winters of 1991-1992 and 1992-1993. No significant difference was found in fungal survival due to depth of burial. Higher winter survival frequencies in the second year were associated with 2-4 C lower average monthly soil temperatures relative to the first year. Survival frequency was higher on membranes than on stems.