Wednesday, November 26, 2014

Weed of the Month for November 2014 is Roughstalk Bluegrass

Roughstalk Bluegrass  

Biology: Roughstalk bluegrass, primarily known by its scientific name (Poa trivialis), is a cool-season perennial grass that can be found throughout the Midwestern United States. Though roughstalk bluegrass can be found in landscapes, roadsides, meadows, and waste areas, it is primarily considered a turfgrass weed. It can successfully germinate in multiple environmental conditions, but it has a preference for moist soils and high levels of shade. This ability to successfully establish in conditions ideal for the growth and development of most turfgrass species, as well as its ability to spread throughout the turfgrass canopy by stolons, make roughstalk bluegrass a common turfgrass weed throughout the state of Indiana.

Identification: Roughstalk bluegrass is a cool-season perennial grass that can be found in both high- or low-maintenance turfgrass throughout the Midwestern United States. Though the plant looks like it has clumping growth patterns, the plant survives from year-to-year through creeping, above-ground stems called stolons, which spread easily throughout the surrounding turfgrass canopy. Seedlings of the plant are generally small and slow to establish compared to other turfgrass varieties. Despite being included in turfgrass seed mixtures for shady areas, roughstalk bluegrass is also a common contaminant of uncertified turfgrass seed mixtures, and will successfully germinate alongside the desired turf species with adequate soil temperature and moisture conditions. Roughstalk bluegrass leaves are folded in the bud with a membranous ligule that can range from absent to very distinct (long) in size (NOTE: when samples are sent to me for identification, it is usually the type with no or very short ligules). The presence of very small, scabrous hairs give the leaf surface and margins a rough feel, thus accounting for the common name ‘roughstalk bluegrass’. The plant has a broad collar and a boat-shaped leaf tip that is characteristic of other bluegrass turf species. The leaves are shiny, and are pale green or yellow-green in color, but they often turn red or maroon during periods of drought or heat stress. Seedheads are produced from mid-May through June in an open panicle similar to that of Kentucky bluegrass. Roughstalk bluegrass can remain green throughout the winter (with some minor leaf-tip burn) and during the summer months it generally goes dormant. Stolons can successfully germinate after many years of prolonged dormancy. It is often confused with other bluegrass species such as annual bluegrass, though it is considerably larger, and Kentucky bluegrass, though it is generally lighter green in color. Annual bluegrass is primarily bunch-type. Kentucky bluegrass has rhizomes (underground creeping stems). Roughstalk bluegrass can also be confused with creeping bentgrass which is also stoloniferous; however, creeping bentgrass is rolled in the bud while roughstalk bluegrass is folded in the bud.  

Rough bluegrass stolon.

New growth emerging from a node on a rough bluegrass stolon in September following summer stress.

Most rough bluegrass samples have a small or absent membranous ligule with no visible auricle present.

Heat stress in summer will start off as a purpling of the leaves.

Patches of rough bluegrass turn brown.

Eventually rough bluegrass patches will enter summer dormancy and appear dead.

This golf course had a lot of rough bluegrass which created a perennial problem of summer decline in their fairways.

Green stolons look like spaghetti.

Green stolons look like spaghetti. Stolons easily pull up in summer when plants are stressed and rooting is poor.

Cultural control: Rough bluegrass likes shady, wet areas. Therefore, reduce irrigation frequency to reduce the spread of this grassy weed. Mowing practices alone will not provide adequate management since roughstalk bluegrass can survive in many of the same environmental conditions and management programs as other desired turfgrass species. The best method of cultural control for roughstalk bluegrass is to avoid contaminating your turf system in the first place by buying certified seed mixtures/blends from a reputable seed company. Carefully read the labels of each seed bag. Unless the seed is advertised as a shade tolerant mixture, make sure roughstalk bluegrass species are not mentioned in the varieties of seed contained within the bag as a 'weed seed'.

Biological control: None known specifically for roughstalk bluegrass.

Chemical control: Small areas and patches of roughstalk bluegrass can possibly be managed by making repeat applications of non-selective herbicides such as glyphosate and glufosinate; however, complete control is difficult due to the survival of creeping stolons.Spring application timings before the stress of summer will aid in the control of rough bluegrass with these non-selective herbicides.

For golf courses and sod farms, other products exist that are not labeled for use in lawns. For more information on these products and on weed control, check out our Turfgrass Weed Control for Professionals Publication.

For archives of past weed of the month postings, visit our Weed of the Month Archive.

Aaron Patton, Turfgrass Extension Specialist
Leslie Beck, Postdoctoral Research Associate


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