Rough bluegrass or roughstalk bluegrass (Poa trivialis) is considered an invasive perennial grass weed that thrives in moist soils and can persist in moderate to heavy shade. Rough bluegrass spreads by stolons and white trailing tillers close to the surface.
Botanical studies estimate that even though rough bluegrass is a perennial, it can potentially produce up to 1,500 seeds per inflorescence.
The specific epithet trivialis is Latin for “found everywhere,” and that is appropriate, since rough bluegrass and annual bluegrass (Poa annua) are consistently listed as the most troublesome and hard-to-control weeds in turf (www.wssa.net/wssa/weed/surveys). Rough bluegrass leaves present a yellow-green color in spring and summer, and circular patches become noticeable in the summer due to its intolerance to heat, drought and diseases.
Postemergence rough bluegrass control in cool-season turfgrass has been limited to spot applications with a nonselective herbicide. Researchers at Virginia Polytechnic Institute and State University (Blacksburg, Va.), however, investigated the possibility
of utilizing PoaCure (Moghu USA) — formulated as 2.3 pounds active ingredient methiozolin per gallon (275.6 grams per liter) — to selectively control rough bluegrass in fairway-height creeping bentgrass. The mode of action of methiozolin
is the disruption of plant cell wall biosynthesis via inhibition of the tyrosine aminotransferase enzyme and is thus classified as a Group 30 herbicide by the Weed Science Society of America. The site of activity is mostly root uptake.
Test plots were located on L-93 creeping bentgrass on a golf course in Radford, Va. Mowing height ranged from 1⁄2 inch (1.3 centimeters) to 21⁄32 inch (1.7 centimeters). At a second golf course in Meadows-of-Dan, Va., mowing height was 13⁄32
inch (1.0 centimeters). Individual plot size was 6 feet × 6 feet (1.8 meters × 1.8 meters) at Radford and 6 feet × 20 feet (1.8 meters × 6.1 meters) at Meadows-of-Dan, and at both sites treatments were arranged in a randomized
standard field study design with three replications.
Treatments were PoaCure at 1.2 fluid ounces per 1,000 square feet (3.8 liters per hectare) applied four times in the fall; 1.7 fluid ounces per 1,000 square feet (5.4 liters per hectare) applied four times in the fall; 1.2 fluid ounces per 1,000 square
feet applied four times in the spring; 1.7 fluid ounces per 1,000 square feet applied four times in the spring; 1.2 fluid ounces per 1,000 square feet applied twice in the fall and twice in the spring; 1.7 fluid ounces per 1,000 square feet applied
twice in the fall and twice in the spring; and a non-treated check. All treatments were applied in 30-gallon water carrier per acre (281 liters per hectare) and also watered-in with 0.2 inch (5.1 millimeters) of irrigation. These field studies were
conducted from fall 2013 through spring 2015.
Visual estimation and line-intersect methods were used to measure rough bluegrass cover within the test plots during the spring and fall. Rough bluegrass plot area cover at the start was 7% at Meadows-of-Dan and 50% at Radford. Creeping bentgrass quality
was assessed visually and by measuring the normalized difference vegetation index.
None of the PoaCure treatment programs injured or negatively impacted creeping bentgrass quality. All PoaCure treatment programs produced an acceptable range of 40% to 85% reduction in rough bluegrass. PoaCure applied at 1.2 fluid ounces per 1,000 square
feet or 1.7 fluid ounces per 1,000 square feet four times in the fall resulted in the greatest reduction of rough bluegrass at 60% to 85%. PoaCure applied at 1.2 fluid ounces per 1,000 square feet or 1.7 fluid ounces per 1,000 square feet four times
in the spring resulted in 40% reduction of rough bluegrass. PoaCure applied at 1.2 fluid ounces per 1,000 square feet or 1.7 fluid ounces per 1,000 square feet twice in the fall and twice in the spring resulted in 40% to 80% reduction in rough bluegrass.
The current PoaCure product application rate is 1.2 fluid ounces per 1,000 square feet, but be sure to read the label thoroughly for more information about application timing and interval recommendations. PoaCure application programs implemented and delivered
over time represent a viable option for suppressing rough bluegrass in creeping bentgrass fairways. With any management strategy, considerations with agronomics, the environment and economics are important to develop an overall sustainable solution.
Source: Rana, S.S., and S.D. Askew. 2017. Long- term roughstalk bluegrass control in creeping bentgrass fairways. Weed Technology 31(5):714-723 (https://doi.org/10.1017/wet.2017.72).
Mike Fidanza, Ph.D., is a professor of plant and soil science in the Division of Science, Berks Campus, at Pennsylvania State University in Reading, Pa. He is a 22-year member of GCSAA.