Written by Travis Miller, MNWR Supervisory Ecologist/Photos by Travis Miller

The Problem

Smooth Brome grass (Bromus inermis) is an exotic invasive perennial grass with an extensive underground system of rhizomes and roots that forms dense stands/sod which excludes native plant species and can significantly reduce habitat quality such as for birds (bobolink and cranes) and insects (pollinators).

Habitats at risk are those with moist soils such as Dry and Mesic Meadows similar to the abiotic conditions of the Island Field (also known as Bobolink Alley), elevated areas along riparian habitat of the Donner und Blitzen River, East Canal, and access points along some of the refuge’s levees.

The extent of smooth brome across the Refuge is still being evaluated, but this invasive plant was not identified as a known concern here prior to the summer of 2022, when surveys for other priority exotic invasives were being inventoried with our contractor Open Range Consulting. The current expanse found in summers 2022 and 2023 is believed to have occurred within the last decade, where invaded sites can be found south of the P Ranch likely the epicenter with small to large patches found all the way to Sodhouse Dam.

Primary mechanism for cause of spread is our waterways, including riverine, irrigation canals and ditches, and overland flow. Secondary mechanism of spread is through established sites expanding rhizomes out into adjacent plant communities.

The Goal

MNWR intends to limit smooth brome spread and its competitive advantages over our desirable plant communities.

Current available tools for treatment are herbicides. For future treatments if other tools become available such as biological, we will look at utilizing those as well.

Effort of rehabilitation will be determined by size of invaded site. Larger treatments will require the greatest investment with the ideal outcome re-establishment of native plants, but we may need to experiment with desirable non-natives that meet our habitat objectives if native plants are unable to establish.

This is a race in time against the invasive plant species that seem to always have the advantage in propagule production, mechanisms for spread, and high success in establishment over our native species.

The Plan

MNWR will begin herbicide treatments in 2024  during this plant’s peak growth period, from mid-June to mid-July, in the effort to cause significant mortality.

Herbicides unfortunately will cause mortality of desirable plant species. Mitigation to reduce native plant losses or impacts to wildlife are:

1. Treat some areas as late as possible (closer to mid-July) when some plant species such as forbs are becoming dormant and to avoid potential exposure to wildlife. Island field and bobolink are examples of this scenario.
2. Be as surgical as possible at the edge of large patches where there is still a sweet of native plant species.

Large patches will need to be revegetated in a three-step process:

1. Follow herbicide treatment in fall of 2024 with a cover crop using a sterile triticale hybrid to temporarily occupy the site. This may require a mechanical treatment as will using a tractor and disc to prepare the soil for seeding. Planting into the sod formed by smooth brome will substantially reduce seed contact with soil for germination and establishment.
2. Re-treat smooth brome July of 2025 that may have been missed.
3. Fall of 2025 seed in desirable plants ideally natives.

Monitoring of pre and post-treatments both large and small invaded sites will be key in determining treatment success and/or failure. Identifying results will inform us on possible future actions that may need to be taken for both known treated sites and for new sites found.

Unfortunately, management direction for smooth brome will be a long-term investment in order to protect wildlife habitats identified in the CCP, and smooth brome has been added to our Invasive Plant Prioritization list for the refuge’s integrated pest management plan as an invasive species of great concern.

Fortunately, we will utilize Malheur National Wildlife Refuge’s Hay and Rake-bunch Graze fee program to support this effort on a year-to-year basis to address smooth brome invasion into our invaluable meadow and riparian habitats. We have been working with the local Harney County Weed Program in past years and will be substantially ramping up our funding to them this year and in coming years. They will not only be addressing smooth brome but other priority species this year that includes phragmites, hybrid cattail, Russian olive trees, and salt cedar.