New Invasive Grass Invades Montana

Noxious weeds have destructive impacts on Montana's landscape including displacing native plant species, increasing soil erosion, and decreasing wildlife habitat and recreational opportunities. Rangeland, pastureland, cropland, forests, and wildlands comprise 92 million acres, or 98 percent, of the total land area in Montana.

Both new and continued infestations of these non-native species not only reduce the productivity of cropland and rangeland, but infestations of noxious weeds also negatively impact wildlife habitat, affecting the vitality and survival of native species due to increased competition for space, nutrients and water, thereby diminishing the productivity and biological diversity of ecosystems.

Until recently, Montana had 35 state listed noxious weed species collaboratively impacting about 8.2 million acres. At its meeting March 21, 2019 the Noxious Weed Listing Workgroup recommended adding ventenata (Ventenata dubia) to the list. The amendment was adopted on June 21st, 2019 and the Montana Department of Agriculture has amended ARM 4.5.208 pertaining to the State Noxious Weed List (Priority 2A), increasing the number of state listed species to 36.

Ventenata, also known as wiregrass or North African grass, is a non-native winter annual grass that is relatively new to Montana and has the potential to negatively impact range, pasture, wild lands, and annual crops. Winter annual weeds emerge in late summer and fall, survive the winter, resume growth in in late spring, and produce seeds in late spring or early summer. Ventenata's low forage value and shallow root structure can lead to decreased agricultural production and increased risk of soil erosion. Ventenata originates from eastern Europe and was first documented in Montana in the mid-1990s. Ventenata infests about 55,000 acres in Montana. Infestations occur in native rangeland, pastures, and along roadsides in several counties including Powell and Lewis & Clark counties.

Ventenata typically grows six to 18 inches tall, with reddish-black nodes, or bulges, along the stem. Seedlings and mature leaves are very narrow and appear to be folded lengthwise. Open and airy seed producing panicles emerge late May through June at which time the stems noticeably harden. Ventenata seeds have bent and twisted awns, or needle-like structures that become developed during June and July, becoming about 1/10th of an inch in length. Each Ventenata plant can produce 15-35 seeds, and dense stands can produce from 2,800 to 3,700 seeds per square foot. This grass is known to spread via roadways and contaminated forage, and the needle-like awns can easily attach to fur, clothing, and machinery.

Management practices include, foremost, maintaining healthy productive stands of perennial grasses and timely detection of new infestations to limit spread. Mowing can have limited success for small infestations, though the wiry grass and bent-nature of the awns are difficult to cut and risk of a second flush of seeds may occur. The herbicides Esplanade 200 SC, Axiom DF, and Sinbar WDG are currently labeled to control ventenata with limited application in rights-of-way and natural areas. Outrider, Plateau, Panoramic and Laramie 25 DF products are labeled for use on cheatgrass and Japanese brome and can also be effective on ventenata. Management recommendations for ventenata control will be refined as more research is conducted.

To address any of the 36 noxious weeds you may encounter in Montana, an important first step is learning how to identify the weeds we are dealing with across the state. While weeds are commonly identified by flower color, you may have to look at other characteristics, including leaf, stem, root system features. A couple of excellent resource for information and photos to help you identify and treat Montana's noxious weeds include the Montana Weed Control Association and the Montana Department of Agriculture websites.

Prevention and early detection can help slow the spread of new invaders and maintain weed-free areas. Contact your Extension agent or county weed coordinator for more information.