Transportation departments face the looming challenge of ever-increasing invasive, annual grasses on roadsides and rights-of-ways. Exotic annual grasses such as Downy brome (cheatgrass, Bromus tectorum L.) and medusahead (Taeniatherum caput-medusae[L.] Nevski) easily disperse seed and readily establish in disturbed areas, such as where road construction or improvements have disturbed vegetation cover and soil. Their persistence along roadsides increases overall costs of roadside management and leads to poor establishment of desirable seeded plant species. Studies have shown, naturally occurring soil bacteria can be used to reduce the competitiveness of weeds. The weed-inhibitory bacteria (Pseudomonas fluorescens strain ACK55; ACK55) can be applied in a roadside setting to reduce the competitiveness of downy brome (cheatgrass), jointed goatgrass, and medusahead, as well as increase plant diversity and reduce the wildfire threat. The objective of this study was to obtain field and scientific data needed to evaluate weed-suppressive bacteria and determine if the bacteria can effectively reduce downy brome (cheatgrass) and medusahead, and allow existing native plant populations to re-establish along ITD roadsides. Researcher Dr. Ann Kennedy treated sections of roadsides along I-84, I-86 and US-95 in Idaho. Twelve sites were treated with weed-suppressive bacteria; 2 of the 12 sites were treated in FY17 (fall of 2016). The bacteria were found to reduce downy brome (cheatgrass) by 30 to 97% in the first two years. Medusahead patches were evident in the control plots, however medusahead was not found in the sites after bacteria application of ACK-55. The sites with the highest downy brome (cheatgrass) reduction occurred on US-95 (MP 1) and I-84 (MP 59; sites #2 & 3) in burned areas with existing desirable perennial plant species. The final report summarizing study findings and best management practices for roadside programs was issued in June 2017. ITD has submitted another research project in 2019, a continuation of this project to collect additional data and organize results for developing long-term management goals and plans. Weed-suppressive bacteria were applied to just over 1,700 acres on private land and just over 8,900 acres on public land in 2014-2017.
Vegetation Management in Transportation Corridors