How to Get Rid of Poa Annua in Bermuda Grass

University of Georgia Extension describes annual bluegrass as lighter green than the surrounding turf, with a coarser leaf and a seedhead you notice. The seedheads are the giveaway in spring: lots of them, even on a lawn you mow. UGA notes that the name is only half right. There is an annual type that lives one cool season, stands more upright, and makes more seed, and a perennial type that hangs on, stays lower, and shows up more in shade, compacted spots, close mowing, frequent irrigation, and high nitrogen. You will not always be able to tell which one you have from the sidewalk. Both are a problem. The perennial type is harder, because a pre-emergent does not stop a plant that is already alive and spreading.

In dormant Bermuda it is obvious, because everything else is tan and the Poa is green. In a zoysia or St. Augustine lawn that holds some color, and in tall fescue, it hides as a grass inside a grass until it seeds and then dies out in the heat, leaving a hole. Henbit and chickweed germinate in the same fall window. They are broadleaves, not this grass. The winter weeds guide covers those two alongside Poa.

UGA says the seed germinates in late summer or early fall once soil temperature falls below 70°F. Seedlings grow in the fall, sit through winter, and flower in spring. A single plant can produce hundreds of seeds even when you mow it, and that seed can sit in the soil for years. Poa likes short days and cool weather, so it outgrows Bermuda while Bermuda is stopped. It often dies when summer heat arrives, unless you keep watering it. Perennial types are the ones more likely to survive if the irrigation never goes off.

The cultural half, from the same UGA bulletin, is straightforward. Water deeply and less often, and do not keep a dormant Bermuda lawn wet just because the Poa looks thirsty. Do not fertilize while the green plant in the yard is the weed. Mow at the high end of the range for your grass going into the germination window so the canopy shades the soil. Core-aerate warm-season grass in summer, with time to fill back in before Poa germinates. Aerating into a sea of open holes during germination is how you plant it. University of Georgia's pest guide puts typical pre-emergent dates at September 1 to 15 in North Georgia and October 1 to 15 in South Georgia. Those are reminders to start checking the soil, not a promise that every ZIP is ready on the first.

Soil is still above 70°F and you are not seeding. This is the pre-emergent window. UGA says the herbicide has to be down before germination, and that it will not kill plants already up or stop perennial Poa from spreading vegetatively. A second application in winter can catch later seedlings if the label allows the split. Water it in right away. UGA wants the herbicide in the top quarter to third of an inch of soil, not stuck on the leaf. The active ingredients UGA lists for this job include dithiopyr, pendimethalin, prodiamine, and bensulide. The same spray stops ryegrass and fescue seed. If you plan to overseed Bermuda with rye for winter color, skip the fall pre-emergent. You get winter color or you get Poa prevention. A standard pre-emergent will not give you both.

Poa is already up, and the Bermuda is fully brown. You missed prevention. Virginia Tech's warm-season calendar is the source for a narrow non-selective option on winter weeds, and only when Bermuda is fully dormant and was not overseeded. The winter weeds guide walks through that case and the lawns where the same spray kills the grass you wanted. Do not improvise it on zoysia, St. Augustine, or anything with green Bermuda in it.

You want a selective spray on warm-season turf. UGA's Bulletin 984 says atrazine or simazine can be used on warm-season grasses for annual bluegrass from November through February, and it says to avoid post-emergent herbicides during spring green-up. The product table lists atrazine for dormant Bermuda, centipede, St. Augustine, and zoysia, and it says not to apply during Bermuda green-up. Some atrazine products are restricted-use professional herbicides. A homeowner bottle still has to name your grass and Poa annua. UGA also says post-emergent sprays belong on small, growing weeds when air temperature is about 60 to 90°F, and that spraying turf stressed by heat or drought injures the grass and works poorly. Read the label for the rate. This page will not invent one.

Track the 70°F line on the soil temperature tracker. The fall application is the reverse of the crabgrass application: crabgrass is soil warming in spring, Poa is soil cooling in fall. When to apply pre-emergent puts both on one calendar.

• Spraying a spring crabgrass preventer in March and expecting it to erase Poa that sprouted in October.
• Applying a fall pre-emergent and then overseeding rye into it.
• Watering and feeding dormant Bermuda so the green tufts look happier. You are raising the weed.
• Spraying a post-emergent in April while Bermuda is greening up. UGA says to stay off post-emergent herbicides during spring green-up.
• Assuming every green winter clump is Poa. Henbit has square stems and purple flowers. Chickweed mats. The control product is not always the same.
• Using a professional atrazine rate, or a product that does not list your grass, because a chart said "warm-season."