Weed-suppressive bacteria (WSB), specifically the D7 and ACK55 strains of Pseudomonas fluorescens, were previously reported to selectively inhibit growth of invasive annual grasses. However, recent studies show highly mixed evidence for WSB effectiveness in field settings.
USGS and Boise State University researchers evaluated the effectiveness of WSB grown in soil vs. agar culture, and tested whether sterilization to remove competing microbes and WSB concentration affected growth of invasive annual grasses. WSB had no effects in soil with or without pre-sterilization, but WSB did inhibit both invasive and native grass growth in agar cultures when applied at high concentration. Bacteria were only partially selective for target weeds at low concentration, and results suggest the desired effect is not reproducible for plants in soil, even when competing microbes are removed. Additional research is needed to determine if, when, where, and how WSB could be effective in field settings.
Lazarus, B.E., Feris, K.P., Germino, M.J., 2020, Weed-suppressive bacteria effects differ in culture compared to in soils and with or without microbial competition and separation of active ingredient: Biological Control, https://doi.org/10.1016/j.biocontrol.2020.104422