Battling Annual Bromes in the Havre Field Office

Story by: Floyd Thompson, Rangeland Management Specialist, Montana/Dakotas State Office; and Jeremy McKellar, Rangeland Management Specialist, Havre Field Office 

What do you do with an allotment that is managed well, but which is still seeing troubling increases of the invasive annual grasses cheatgrass and Japanese brome?  

This is the dilemma Havre Field Office Rangeland Management Specialist Jeremy McKellar is tackling. The Rivers Edge allotment has been grazed in the dormant season for a couple of decades, so the native grasses and forbs are generally robust and healthy. Even so, the annual bromes have invaded.  

The Rivers Edge allotment consists of bluffs, coulees, and flats adjacent to the Marias River in the middle of Montana’s “golden triangle”—the premier grain growing region in the state. The allotment pastures are islands of native vegetation in the middle of miles of grainfields. Unfortunately, the grainfields also supply plenty of cheatgrass seed for animals, humans, and wind to spread onto the allotment. 

The dormant season grazing use period caused substantial amounts of plant litter to build up in the allotment. Although litter is generally a good thing and an indicator of soil and site stability, as well as a contributor to hydrologic and biotic function, too much litter can be a problem as well. In the northern great plains, researchers at the Miles City Agricultural Research Service station report that due to litter buildup more annual brome is observed at sites that are not grazed than at moderately grazed locations. 

Jeremy is working with the permittee to implement a multi-faceted approach to address the problem. The first change is to increase grazing use in the spring and summer when the grasses (including annual bromes) are more palatable to reduce the litter accumulation. Additionally, flexible terms and conditions were added to the permit to account for varying year-to-year weather conditions and to provide pasture rotation changes to maintain plant health and vigor. 

Secondly, Jeremy set up a series of test plots to determine whether herbicide treatments will reduce the annual brome infestations while maintaining or improving the health and resiliency of the native grass and forb communities.  

Results after last year’s fall treatments look promising. Before treatment, there were an average of 2,935 individual

plants per square meter; after treatment, the test plots had just 14 plants per square meter -- a decrease of more than 99 percent. Jeremy is monitoring the plots to determine the effects on the native plant populations, whether the annual bromes will return, and whether the treatments should be expanded to other areas in the allotment. Additionally, Jeremy is paying close attention to the cost of the test plot treatments for potential future project cost-benefit analyses. 

The battle against annual bromes requires many innovative approaches. The knowledge gained from the Rivers Edge allotment will help inform BLM’s future management efforts in the northern Great Plains.