The common name, annual bluegrass is a bit deceptive since there are two variations to the species, Poa annua. One, Poa annua var. annua is a true annual and will set seed and die at the end of one growing season. The other form, Poa annua var. reptans is a perennial and its plants live from year to year. It varies from the common turfgrass, Kentucky bluegrass (Poa pratensis), however, both species have leaves that curve up like the bow of a boat which is a distinguishing trait.

Annual bluegrass is native to Europe but has spread across the world as a weed species. Unlike other forms of bluegrass, it is undesirable as a turfgrass (lawn) species. It is especially troublesome because it can withstand very low mowing heights and still produce plenty of seed. The annual form is more common in home lawns while the perennial form is found mostly on golf courses.

The annual form has a fairly weak, shallow root system so it does best in irrigated situations. It may turn brown and suffer more from droughty situations than other grass species. In hot, dry situations, it may actually die in mid-summer in some areas.
 

One control options is to try to prevent the spread of seed from site to site. At times, lawn mowing equipment may carry seeds if not cleaned off when moving between locations.

If you just discover a few plants in a limited area, removing them before they set seed may do the trick. This is, of course, a limited option.

As with all types of annual weeds in lawns, perhaps the best control is to do the things needed to grow a thick, vigorous turfgrass. For annual seeds to germinate, they usually need some bare soil and no taller plants hovering above to shade the ground. To have these conditions in the lawn, means that the desirable turfgrasses are not growing to their best vigor.

Finally, there are pre-emergent herbicides that are labeled for use on annual bluegrass. Proper timing is extremely important since these products will not work on plants after they have germinated and have started to grow. Check with your local Extension Service to determine the proper products and timing for your area.

A few new post-emergent herbicides may also be available for use on growing plants of annual bluegrass. Again, the timing is everything because once the plants have set seed, it does little good to kill the plant since the next generation has already been assured.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

 

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