Re-visiting Lawn troubles…weed grasses – poa and velvetgrass

May is the “Go!” month for lawns.  As the soil warms, top growth accelerates and roots grow quickly.  That goes for weed grasses too, like annual bluegrass, velvetgrass, bentgrass and quackgrass.  First up is Poa…

From MSU on Poa species;

“Annual bluegrass is unique among weeds. There is probably no other weed that is so widely adapted to variations in mowing height, site conditions and cultural practices.

Annual bluegrass is the most common and widely distributed grassy weed in the world. It is mentioned as a weed in nearly every plant commodity.

Turfgrass management professionals, including golf course superintendents, sports field managers, sod producers, and lawncare operators, have spent years trying to eradicate annual bluegrass from their turf swards. Annual bluegrass (Poa) is one of the most invasive weeds in turfgrass stands. It is also one of the most difficult to control.

Efforts to find chemical controls for Poa have been thwarted by its diverse genetic make-up. Poa is officially described as a cool-season winter annual. Winter annuals are plants that germinate in late summer to early-fall, overwinter, and produce seed in the spring. Typical winter annuals die soon after seed production as daytime air temperatures increase.

Poa annua, although commonly referred to as annual bluegrass, is actually a diverse group of different biotypes with varying characteristics. Annual bluegrasses in warmer climates like the southern U.S., do indeed perform as a typical winter annuals. These “annual” bluegrasses are classified as Poa annua var. annua L. Timm. In the northern part of the U.S. and much of Canada there are biotypes that produce seed in the spring and then continue to grow as perennials. This somewhat peskier bluegrass is termed Poa annua var. reptans (Hauskn) Timm.

The fun doesn’t stop there. Somewhere between true bunch-type annual bluegrass and stoloniferous [perennial] annual bluegrass are hundreds if not thousands of different biotypes.

Clearly, identifying controls that have excellent activity on annua, reptans, and everything in-between has been difficult for good reason. These biotypes are not just segregated by climatic region or area of the country. It is possible, in-fact likely, to have several biotypes of Poa on the same property. The segregation is not only determined by climatic zone, but also by management and cultural conditions such as irrigation, mowing height, and compaction.

Poa populations are so diverse that they can easily adapt to everything from unirrigated roughs to closely maintained putting greens. This diversity makes Poa a bit of a moving target. Predictable Poa control would likely exist if 100 percent of the Poa population was truly annual.

Objections to annual bluegrass are most often related to seed production (which can happen in any month in moderate climates), surface interference, color and disease susceptibility.”

Annual Bluegrass (Poa Annua)


Copyright 2004-2013, Ronald Calhoun.


Copyright 2004-2013, Ronald Calhoun.


Copyright 2004-2013, Ronald Calhoun.


Poa trivialis lays flat, grows faster, has broader stems and is lighter green this time of year, so you can’t miss it.

Maintenance practices to avoid

Overwatering, especially in shady areas, will predispose turfgrass to invasion.  Use deep and infrequent irrigation to discourage the development of shallow-rooted Poa.  Also, avoid cultural practices as well as use patterns that tend to promote soil compaction.  Catch clippings and dispose offsite as mulch mowing will spread seed.  Aeration and mechanical dethatching will spread seed so delay these practices until there are no visible seed heads before attempting either one.


No single control procedure has been successful in controlling poa in turfgrass.  However, hand removal of solitary infestations has been successful when practiced diligently. Open spots should be overseeded to establish a vigorous stand of grass. Removal of grass clippings may help reduce the number of seeds that reach the soil, but will not eliminate the possibility.  Seed is spread by foot traffic, mowing and other machinery, birds and wind so the chance for some level of infestation is very high.

Periodic pre-emergence herbicide treatments will reduce seed germination considerably but have no effect on germinated grass plants.  These treatments should be applied prior to seed head formation, usually early spring and late summer.  Spot treatment of young seedlings with Roundup is effective but needs to be done before the plant begins to seed.  We have a tool for sale that allows spot treatment from a standing position without over-spray damage for use in both lawns and ornamental beds.  Hand removal of seedling plants and overseeding coupled with pre-emergence treatments gives the best control of poa.  Newly sodded lawns will be less vulnerable to poa invasion and with vigilant hand removal and a pre-emergence treatment program starting at installation can be kept free of poa.  But without weed grass maintenance a new sod lawn could have visible poa within the first 3 years, maybe sooner.   Surface seeded lawns are even more prone to invasion, the same is true with hyroseeded lawns.   So, Poa is here to stay but there are ways to minimize the spread… or just learn to live with its bad habits and encourage maximum performance or plan to renovate when weed grasses can’t be tolerated anymore.

We can help with a plan of action for renovation, just ring us up.



???????????This bad guy can be controlled!  After years with no solution except digging this weed grass out or treating with RoundUp, and over-seeding, we now have a selective herbicide that will control both velvetgrass and bentgrass and leave the desirable species unscathed. 

3 treatments are required spaced 2-3 weeks apart.  The velvet and bent grasses turn snow white after treatment as the herbicide stops the production of chlorophyll, eventually killing the plant. The treatments will control large and small grass plants, so the look can be quite dramatic if the weed grass population is high. The product manufacturer posted this comment relative to the white grass, “It looks like it snowed, but only on your lawn!”. 

Over-seeding may be required if the dying grasses leave large bare spots.  We can help you with information on how to do the over-seeding yourself or refer you to a local lawn renovation firm that can do it for you. 

Weedgrass identification and treatment quotes are gladly given free of charge within 30 miles, roundtrip*, from the Washington State Capitol, just ring us up or email a request.  If the weed grass population is too numerous to warrant a selective control approach, a total kill using RoundUp, which we can do, and renovation/reseeding process may be the best choice. If this option is chosen, and the RoundUp treatment is approved, technical renovation information will be provided including contact information for qualified renovation firms.

*Within 30 miles, roundtrip, from the Washington State Capitol.  A $1.00 per mile fee will be assessed for trips in excess of 30 miles roundtrip but waived if treatments are recommended and approved.