Weed of the week: Roughstalk bluegrass (Poa trivialis)

April 23, 2010 in Extension

Roughstalk bluegrass (Poa trivialis) is one of the top three perennial grass weeds in Pennsylvania. Every spring I receive reports of yellow-green patches of roughstalk bluegrass invading lawns, golf course fairways, and sports fields, and this year in no exception. Three samples were sent to my office last week, and I’m sure more will arrive in the coming weeks.

Roughstalk bluegrass is occasionally used as a turfgrass on shaded sites that are poorly drained, or as a temporary grass for winter play on golf courses in the southern U.S. However, in Pennsylvania it is more common as a weed grass that grows over desirable grasses via runners or stolons. This species looks similar to other turfgrasses, except that it produces a yellow-green color, and grows in patches. Sometimes these patches are mistaken for diseased turf, and have even been sprayed with fungicides. Individual plants have a shiny appearance on the back of the leaf blade (abaxial surface), and possess stolons that creep along the soil surface and over the top of desirable turf. Roughstalk bluegrass spreads quickly during cool weather and/or in shaded areas, but tends to turn brown and die back in sunny areas during the summer. Unfortunately, this species always seems to survive the heat and drought of summer to live for another day.

Roughstalk bluegrass can find its way into turf as a contaminant in turfgrass seed, or as seed in soil that was brought from an infested area into a new site. Once it is in the stand, it’s almost impossible to determine where the roughstalk bluegrass seed came from. Seed of this species looks virtually identical to Kentucky bluegrass, and can easily escape the seed inspection process. Professional turfgrass managers should protect themselves from roughstalk bluegrass contamination by buying certified seed from high-quality sources, and perhaps employ the services of a private seed inspection lab if the seed will be used for extensive, high value plantings (such as a new golf course).

If you find this weed growing in your turf, try to suppress it before it begins to spread into large patches. Professional turf managers can try using Certainty® (sulfosulfuron); golf course managers can use Certainty® or Velocity® (bispyribac sodium) for suppressing roughstalk bluegrass.

Certainty® has worked reasonably well in suppressing roughstalk bluegrass in trials conducted at Penn State. However, it’s almost impossible to completely eradicate this species…with any herbicide. Certainty® is labeled for use on Kentucky bluegrass and for perennial ryegrass mixed with Kentucky bluegrass at rates used for roughstalk bluegrass control. Interestingly, the label lists perennial ryegrass as “an additional weed controlled”, but only at high rates (rates between 1.25 and 2.0 oz per acre). Certainty® will control tall fescue, so if tall fescue makes up a portion of your turf, you should not use this product. Certainty® is also labeled for control of roughstalk bluegrass in creeping bentgrass golf course fairways, approaches and tees.