Integration of a fungal pathogen with herbicides may enhance melaleuca control efforts in South Florida. Hyphal inoculum of four Botryosphaeria ribis Gross & Duggar isolates were evaluated in vitro for compatibility with imazapyr, glyphosate, and a surfactant. Imazapyr at 12 to 60 mg ai/ml did not cause significant loss of inoculum viability in all four isolates within 2 h after mixing. After 24 h, inoculum viability of isolate BR-4 remained unchanged at these imazapyr concentrations, but viability of BR-1 through BR-3 was reduced. Glyphosate at the lowest concentration (32 mg ai/ml) significantly reduced inoculum viability of all isolates within 2 h. Initially, the inoculum viability of all isolates remained unaffected by 1, 5, and 10% (v/v) surfactant concentrations. After 24 h, the surfactant reduced inoculum viability of BR-2, BR-3, and BR-4 inconsistently between experiments, while the inoculum viability of BR-1 was reduced significantly at all concentrations. Mixing of the lowest concentrations of imazapyr, glyphosate, and surfactant significantly reduced inoculum viability within 2 h. This corresponded to the results obtained for glyphosate alone. These results show that hyphal inoculum of B. ribis may be mixed with imazapyr and surfactant for field applications, but mixing the fungus with glyphosate may not be as efficacious.

Field studies were conducted with a biocontrol agent, Pseudomonas syringae pv. tagetis, to determine the optimal application parameters for controlling woollyleaf bursage, a pernicious perennial weed on the Texas Southern High Plains. Parameters investigated were bacterial concentration, time, season, and frequency of application. Pseudomonas syringae pv. tagetis concentration ranging from 104 to 108 colony forming units (CFU)/ml produced similar incidence of disease on woollyleaf bursage. Weekly, biweekly, and triweekly applications were found to be equally effective. Optimal time for application of P. syringae pv. tagetis was at midday. A single application in April, May, or June resulted in higher incidence of disease for 5 wk than the noninoculated plots, whereas single applications in July and August were not consistently different from the noninoculated plots. Weed density was negatively correlated with disease incidence for April, July, and August applications, particularly when correlations were based on disease incidence from 1 to 4 wk prior to weed density measurement. Weed densities during 1997 were lower at the end of the year when bacteria applications were made in April, May, or June, as opposed to July or August, or plots were not inoculated. In 1998, weed density was lower when bacteria applications were made in April as opposed to May or June. These investigations indicate that P. syringae pv. tagetis does infect woollyleaf bursage on the Texas southern High Plains.