Improvements to the Pesta Formulation to Promote Survival and Dispersal of Pseudomonas fluorescens BRG100, Green Foxtail Bioherbicide

A modified pesta granule was developed for Pseudomonas fluorescens BRG100, a bioherbicidal bacterium for grass weeds, green foxtail (Setaria viridis) and wild oat (Avena fatua). This study reports: i) the effect of formulation water activity (aw) on survival of P. fluorescens BRG100 and, ii) the effect of starch on disintegration and dispersal of a green fluorescent protein transformant of P. fluorescens BRG100 from pesta in laboratory sand columns. The long-term refrigerated storage stability of P. fluorescens BRG100 was examined in pesta granules dried to different aw. Drying pesta to 0.3 aw stabilized the population of P. fluorescens BRG100 for 16 months at 8.5 log10 cfu/g. When pesta was dried to 0.8 aw, P. fluorescens BRG100 population decreased to 7.3 log10 cfu/g over six months. The impact of starch addition (corn, pea, rice and potato) to pesta and concentration (13% and 26%, wt/wt) on the disintegration rate of pesta granules was determined with laser diffractometry. The order of fast to slow disintegration following starch amendment was pea>potato>corn> rice. Increasing pea, potato and corn starch content from 13 to 26% promoted faster disintegration of pesta, conversely, increasing rice starch content decreased disintegration. Half-life disintegration profiles were determined with pea starch amended pesta (26% w/w) being most rapid, 0.8 minute, rice starch (26% w/w) amended pesta was slowest, 4 minutes and non-amended pesta, 2.5 minutes. P. fluorescens BRG100gfp was detected 2 hr earlier in the middle and bottom sections of the sand columns from corn starch amended (26%) pesta than from non-amended pesta. The ability to produce pesta granules with different disintegration and bioherbicide release characteristics provides the formulator with the potential to design pesta that insures the active ingredient is delivered to the pest when it is most susceptible. _____________________________________________________________________________________________________________