Formulation of Bacteria for Biological Weed Control Using the Stabileze Method

Two plant pathogenic Pseudomonas spp. were formulated using the 'Stabileze' method which involves the incorporation of bacteria in a water-absorbent starch matrix with oil and sucrose, then granulating the matrix with hydrated silica. In one experiment, P. syringae pv. tabaci formulated with the standard Stabileze formula was evaluated for storage viability at -15, 2 and 22°C. Bacteria stored for 1 year at -15 and 2°C lost only 0.2 and 0.5 log 10 colony forming units (CFU) g -1 respectively compared to a loss of log 10 3.5 CFU at 22°C. In a second experiment, the same pathogen was evaluated using variations of the formula with and without oil, and with and without sucrose. P.s. pv. tabaci formulated with sucrose and oil in combination, and sucrose and oil alone survived better than the formulation without oil or sucrose. A third experiment tested the effect of four levels of oil and four levels of sucrose (4 ×4 factorial) on survival of P.s. pv. tagetis over a 28 month period. Sucrose alone enhanced survival more than oil alone, and the beneficial effect of the sucrose was reduced when it was combined with oil. These experiments suggest that the Stabileze protocol is effective for stabilizing bacteria, but there are differences in response to different formulation components between species of bacteria.