Poa Anna growing in bermudagrass turfAnnual 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, or Poa Annua, 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 lawn care operators such as LawnAmerica, have spent years trying to eradicate annual bluegrass from their turf swards. Annual bluegrass (Poa) is one of the most invasive weeds in turf grass stands. It is also one of the most difficult to control.

This spring has been the perfect storm for annual bluegrass invasion into Tulsa area lawns.  The summer drought thinned much of the bermudagrass, so that it is not as strong and dense this spring coming out of dormancy,  Then our spring has been so cold, that the bermudagrass is having a hard time growing, to the point of many folks not even mowing their turf yet.  Poa Annua loves cool, moist weather as we are having, so it's loving this weather, and continuing to grow just fine.  As soon as it turns really hot, the bermudagrass will take off, help choke out weeds such as Poa, and the Poa Annua will die out naturally.

It is a prolific seeder, so those seeds will be just waiting to germinate and start the whole cycle again with the first cool rains of early fall.  Homeowners need to apply a pre-emergent herbicide in early fall before the weed seeds germinate to stop next year's crop.  LawnAmerica applies a special product later in fall which is both a pre and a post-emergent herbicide, which controls the weeds.  The problem is that some strands of Poa have deleloped resistance to this chemical control.  Some strands of Poa can actually perform more like a perinnial, and survive for many years.  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.  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.

One thing is for sure though, that as the summer heats up, and bermudagrass is being mowed weekly, Poa Annua will not be around, and if it is, will not be evident.  Mowing at a tall mowing height will help with weed control, as with all weeds, as we move into the summer months.