Poa Trivialis–A Pest on the Rise?

I have been informed that rough bluegrass seems to be an increasingly common contaminant in seed mixes. Rough bluegrass can be desirable when planted in wet, shades settings, but it is normally considered to be undesirable when it invades other turfgrasses due to the yellow-green patches it forms.

Why is rough bluegrass becoming a more common intruder? Currently, in Cincinnati, we are experiencing cool, wet weather that favors the development of Poa trivialis. On a larger scale, the increase in rough bluegrass problems can perhaps be attributed to two reasons. First, more Poa trivialis sees it being produced in the Pacific Northwest for use as a winter overseeding species in the southern U.S. Because more seed is being produced, more seed is available to contaminate other seed lots and fields. Second, there is difficulty in separating Poa trivialis seed from that of other species, especially Kentucky bluegrass (Poa pratensis). Reportedly, seed laboratories vary in ability to distinguish between the two species.

The Plant

Rough bluegrass is perennial, stoloniferous grass that forms dense, yellow-green patches, especially in moist, fertile, fine-textured soils. The sheath is purple or green, rough, and split. Its vernation is folded and the membranous ligule is large either pointed and entire or somewhat toothed. There are no auricles. The blades have a rough margin, boat-shaped tip, and glossy underside.

Controlling Poa Trivialis

There are no labeled selective controls for rough bluegrass; the use of nonselective controls, such as glyphosate, is recommended. Be sure to read, understand, and follow all labeled directions before using any pesticides. When trying to mechanically eliminate patches of Poa trivialis, be sure to remove all stolons that may be moving into desirable turf.

When purchasing seed, buy only high-quality seed with small quantities of crop seed and inert material, and deal only with reputable producers and dealers. Unfortunately, even under the most demanding production conditions, trace quantities of Poa trivialis seed may be present in seed lots, so obtaining a lot that is totally free of this seed may be extremely difficult.