Weed-suppressive bacteria fail to control Bromus tectorum

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Two weed-suppressive bacteria strains of Pseudomonas fluorescens, known as ACK55 and D7, have been shown to reduce these exotic grass populations in eastern Washington, yet little is known about the efficacy of these or other weed-suppressive bacteria in other areas. Researchers tested the effects of ACK55 and D7 on Bromus tectorum both in the laboratory and at field sites in Montana and Wyoming. The bacteria strains reduced Bromus tectorum germination and root and shoot lengths in Petri-plates, but had no effect on plants during growth chamber plant-soil bioassays or field experiments. Bromus arvensis, a species similar to Bromus tectorum, was also unaffected by the weed-suppressive bacteria. Findings contribute to a growing body of evidence that the ACK55 and D7 are not reliable tools for controlling Bromus tectorum in the Northern Great Plains, Central Rocky Mountains, and elsewhere.