Annual Bluegrass in the Lawn?

In full sunlight, annual bluegrass can take on a slightly red hue when seeding. It is quite lovely. Unless, of course, it is in your lawn. Then it is a nuisance. Annual bluegrass, formally called poa annua, competes with tall fescue in the fall and slows the green up of bermuda and zoysia lawns in the spring. Quite the annoying weed.

A Weed by Another Name

Annual bluegrass is a cool-season annual grassy weed. Translating that statement it is a grass, as opposed to a broadleaf weed, that grows in cool weather, September through April, and dies when it gets hot. It’s not just here in North Carolina, but pretty much everywhere. We are certainly grateful that in North Carolina this weed perishes once we have 80 degree temperatures for about a week. Over the years, we have developed a twisted fondness for referring to annual bluegrass by other names. Our code names for this grassy weed reflect our experience with customers and our battles to overcome it.

Winter Fescue (Annual Bluegrass)

When poa annua germinates in the fall, it is often side-by-side with seedings of tall fescue and easily confused as tall fescue seedlings. Upon close inspection, it can be readily distinguished but early on, say October through January, you really have to look close. It is a lighter green than mature tall fescue, but so are the new fall seedlings of tall fescue. As a result, this grassy weed does not stand out to most home owners until the seed heads start to develop. How do I know? When do you think all the phone calls start? And do they start … but this why we sometimes call it “winter fescue”.

In warm-season lawns, such as bermuda, zoysia or centipede, the annual bluegrass is very visible as the turfgrass has turned brown for a winter sleep. The bright green annual bluegrass stands out very well in these lawns. There are control materials that can help manage annual bluegrass in warm-season lawns, but they cannot be used on tall fescue.

Winter Crabgrass (Annual Bluegrass)

The worst pattern we see for tall fescue lawns is an annual bluegrass/crabgrass cycle. Annual bluegrass does not grow in a thick lawn. This grassy weed takes up in thin and bare spots especially in warm, wet winters, such as this past one. But no problem, right? It will just die off sometime around May and it is gone. Finished. Kaput. Finito. Problem solved.

Not quite. By the time the annual bluegrass is dead, crabgrass and broadleaf weeds are off and running. Guess where they like to grow? Of course, in the same spots. These areas usually back fill with crabgrass creating a spiraling cycle of that only improves if measures are taken to break the cycle. Crabgrass will not die on its own until the 1st hard frost. By then, the soils are too cold to germinate tall fescue. Annual bluegrass doesn’t mind. It will continue to germinate during every warm period of the winter.

How to get rid of Annual Bluegrass

Breaking the cycle

As pointed out above, the cycle must be broken. Crabgrass reducers such as pre-emergents in spring certainly help control the crabgrass. Bare and thin spots are where these control materials are going to breakdown first. Pre-emergent manufacturers cite up to 70% control of crabgrass. The rest of the control must come from the lawn shielding the soil from the sun. Remember, our summers are long and hot, ok, not Texas hot or Texas long but you don’t grow tall fescue in Texas. As a result, you are likely to still have some crabgarss to clean up at the end of the summer prior to your “fall” seeding if you had annual bluegrass over the prior winter. I put “fall” in quotes because we have had 90 degree temps into October for the last three years. Fall and 90 degrees are two things that don’t go together in my mind.

Using a pre-emergent in the fall to slow the germination of annual bluegrass is a risky strategy as the pre-emergent will impact the root development of your new tall fescue seedlings. Definitely not recommended. Growing roots is the key to getting tall fescue through the following summer.

Preparation is the Key to Avoid Annual Bluegrass

This leaves a good clean up late summer to prepare for seeding. Be mindful of product labels as many products used to control weeds have seeding restrictions associated with their use. A seeding restriction indicates that if used at a labelled rate, it may have an impact upon the successful establishment of new seedlings. Translation: it can kill your seedlings. Of course, you always read the label prior to use. Well, only if you want to know how to use the control material properly.

The better the soil is prepared for the seeding, the better the outcome. The less competition from other plants in the lawn during seeding, the more seedlings you get. More tall fescue seedlngs, fewer annual bluegrass seedlings. And maintain the turf canopy, or turf cover, of the soil. Once the summer sun starts directly shining on soil in a tall fescue lawn, all heck breaks loose.

Annual Bluegrass is a Symptom

Persistent annual bluegrass, bluegrass that comes up every year, is a symptom of unresolved problems in the lawn. The starting place is to ask whether your lawn is the best grass for North Carolina. Growing turf under the wrong conditions always yields sparse turf unable to compete with weeds.

If possible, fix poor drainage or compacted soils. While annual bluegrass doesn’t require such conditions to grow it can thrive under conditions that cause other grasses to die. It can also be a sign of poor cultural practices such as short or infrequent mowing. It can be obstructions creating poor air flow promoting fungal diseases that thin the turf. Maybe fall seedings are performed too late and allowing the annual bluegrass to get a head start. Maybe leaves aren’t promptly removed during the fall, killing the tall fescue and creating opportunity for annual bluegrass. This is just a short list. Observe your lawn across the season.

Annual bluegrass is telling you a story about your lawn. Listen to that story. If you can address the underlying causes, then controlling annual bluegrass is not that difficult. For more resources, consider the folks over at TurfFiles for a more scientific description. If you need help, just contact us.