Annual bluegrass (Poa annua) is thought to have originated from a hybrid of Poa infirma (weak bluegrass) and Poa supina (creeping meadow-grass) that occurred approximately 2.5 million years ago in the interglacial ice ages of Europe.
Annual bluegrass is widespread around the world. Its presence has been observed on all continents, including Antarctica; though, it is most prominent in temperate climates.
Annual bluegrass is typically classified as an annual comprised of numerous biotypes or “populations.” Many of these biotypes are also capable of perenniating, meaning that they may exist in a vegetative state – producing viable seed throughout the year.
Though perennials are much less common than the annual biotypes, they tend to occur in frequently mown or grazed scenarios in temperate climates with adequate year round moisture. In fact, some of the most lauded golf greens in the world are composed of annual bluegrass, including: Pebble Beach, Oakmont, and the more recently converted Chambers Bay.
Annual bluegrass has historically been an important weed of many, if not most, commodity and specialty crops. The extensive reliance upon herbicides as the primary means of control has led to almost overwhelming presence of herbicide resistance. There are very few commonly utilized herbicides that annual bluegrass has not developed resistance to – albeit often in isolated or unique populations.
The growing concern among many turfgrass managers and scientists is that we may no longer have effective chemical means of controlling annual bluegrass.