Poanna Annual Bluegrass?

A serious spring & summer weed problem


Star-Tip 1055

Gardening Tips for successful and beautiful Landscapes and Gardens



Many questions have been submitted on line and to our offices regarding control annual bluegrass in our lawns during the spring and summer.


The scientific name is; Poa annua and is often referred to as Poanna. It can be distinguished from other grasses by its typical leaf tip which is shaped like the bow of a boat. Also you will recognize it by its different shade of green, and the fact that it usually forms little clumps.


Spring Control: Poanna is prolific in seed head formation in mid-spring. If you did not apply a pre-emergent during October and February, you will want to do this immediately. The fewer of these seeds that germinate during the spring the better. If a single patch of annual bluegrass is found, remove it quickly with a hand tool before seed production starts.


Summer Control: Unfortunately, there is very little that can be done during the summer to control Poanna other than to regularly mow the grass to reduce seed head numbers and improve uniformity.  Poa is a true winter annual plant. It germinates in the fall, produces seed in the spring, and dies. The plant is nearing death in late summer, so any attempts with post emergent control at this time are pretty much pointless. 


Fall Control: Poanna is an problem every year because of the prolific number of seeds that it produces, so donít plan on ever eradicating it from your lawn. You will be able to manage it if you stick to a consistent treatment routine, and the fall is the most important time to take measures against your Poanna problem. Apply pre-emergent herbicide. Pre emergent herbicides prevent seeds from germinating, but do not kill established grasses.









Though it may not be any help with your current weedy mess, the best bet to reduce Poanna for next spring is to plan on making a fall pre emergent herbicide application in the first couple of weeks of September.  Make a note to do this on your calendars now - so you wonít forget!  This control strategy works well on both Poanna and a whole host of other winter annual broadleaf weeds.




Caution; IF you plan on seeding any cool season grasses next fall you can not use a pre-emergent before seeding. Most pre emergent herbicides do not differentiate between weed seeds and desirable turf seeds. If you must reseed a cool-season turf, skip the February application of pre emergent and try over-seeding in early May. Youíll need to make every effort to help the new seeds germinate and establish. Proper soil preparation, watering and fertilization must be done.

If you intend growing warm-season turf grasses, you have the added option of treating your winter grassy weeds with a non-selective herbicide such as glyphosate (Round Up/ Compleet) when the turf is fully dormant, an option not available for cool-season turf grass lawns. 


It would be nice to think that after struggling with weeds all summer, the fall and winter would provide a break from the chores of weed control. However, many lawn weeds begin their life cycle in the late summer and early fall when temperatures are more moderate. They grow during the winter and die in the summer, when temperatures are high. This fall take some action if you want to have better control of your lawn weeds next summer. Remember, your poanna will be dormant and not so visible in the fall, donít let this fool you!











2007, Star Nursery, Inc.Copy Provided courtesy of Star Nursery www.StarNursery.com