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Invasive Grass: Ventenata

2023 Winter
by Jane Mangold
is the MSU Extension Invasive Weeds Specialist.

Invasive grasses such as ventenata may degrade plant communities and reduce suitable habitat for livestock and wildlife. Prevention and early detection can help slow the spread of new invaders and maintain weed-free areas.

Ventenata (Ventenata dubia), also known as wiregrass or North African wiregrass, is a non-native winter annual grass relatively new to Montana and has the potential to impact range, pasture, natural areas and wildlands. Its low forage value and shallow root structure can lead to decreased agricultural production and increased risk of soil erosion.

Ventenata originated from eastern Europe, western Asia, and northern Africa and was first found in North America in the early 1950s in Washington and Idaho. Ventenata was first documented in Montana in the mid-1990s. Montana listed ventenata as a Priority 2A noxious weed in 2019 due to known infestations and continual spread in native rangeland, pastures, and along roadsides. Isolated infestations occur from northwestern Montana through southeastern Montana (Figure 1).

Ventenata is a winter annual grass that typically grows 6-18 inches tall. It has a distinguishing long, membranous ligule (up to 0.3 inches in length) and reddish-black nodes along the stem (Figure 2). Seedlings and mature leaves are narrow and folded lengthwise. Open and airy panicles emerge in late June through July (Figure 3), when the stems noticeably harden. Ventenata seeds have bent awns, similar to wild oat (Avena fatua).

Ventenata mainly germinates in the fall, but some germination can occur in spring. It is adapted to Mediterranean climates with cool, wet winters and hot, dry summers. In Montana, ventenata is invading rangeland, pastures, natural areas (e.g., parks and open spaces), forests, and roadsides. Field observations suggest it can grow in areas with moderate annual precipitation ranging from 14 to 44 inches and elevations ranging from 33 to 5,900 feet.

Ventenata reproduces by seeds. Each plant produces about 15-35 seeds. Dense stands of ventenata can produce from 2,800 to 3,700 seeds/ft2. Most seeds grow the first year, but some seeds may live as long as three years. It is known to spread via roadways, contaminated forage, and by clinging to anything walking through it like people, livestock, and wildlife. Awns can easily attach to fur, clothing, and machinery.

Ventenata has caused substantial ecological and economic impacts in perennial grass habitats. These impacts are less understood for Montana; however, ventenata is generally unpalatable for livestock and wildlife and can decrease forage value. Additionally, the shallow root system creates conditions conducive to soil erosion.

Maintaining healthy productive stands of perennial grasses and early detection of infestations can limit invasion by ventenata. Mowing has limited success for small infestations as the wiry grass and bent nature of the awns are difficult to cut and a second flush of seeds may occur. Grazing is not an option as livestock tend to avoid the grass due to its high silica content and thin, wiry stature.

The active ingredients indaziflam (RejuvraTM), imazapic (Plateau®, Panoramic 2SL), sulfosulfuron (Outrider®), and rimsulfuron (Matrix®, Laramie 25DF) are chemical options for controlling ventenata. In a field trial in southwestern Montana, a single application of indaziflam resulted in over 90% control of ventenata over five years, and there was evidence that the single application depleted the soil seed bank during that time. Other research in Montana has indicated that products containing imazapic or rimsulfuron are also effective for providing shorter-term (e.g., one year) control. Further research on chemical and cultural control methods is underway, and management recommendations will continue to be refined.

If you suspect that you may have found ventenata, contact the local Extension agent, county weed coordinator, or the Montana State University Schutter Diagnostic Lab.

Additional resources:

Ventenata MontGuide

Identifying Ventenata Early in Summer

Identifying Invasive Annual Grasses in Montana