Poa problems

Poa annua is more related to turfgrass than broadleaves, so it’s hard to find a solution to control it and not kill off the turf. (Photo: Nufarm)

Poa annua, or annual bluegrass, presents a problem to lawn care operators (LCOs) because it’s a grass and not a broadleaf weed.

“Poa control in lawns is difficult,” says Aaron Hathaway, technical services manager for Nufarm. “Anytime you are trying to selectively control a grass in other grasses, it’s tricky because they are more closely related than broadleaves and grasses.” For this reason, he says it’s harder to find a chemistry that will selectively kill Poa but not turfgrass.

Dean Mosdell, western technical manager for Syngenta, advocates for strong control of Poa because of its rapidly proliferating seeds.

“Allowing Poa to survive in the lawn will create more weed seeds to combat next year,” he says, noting that any Poa escaping a preemergent application should be controlled with a postemergent herbicide or mechanically removed.

Hathaway, Mosdell and Jamie Heydinger, national lawn/landscape and key accounts manager for Nufarm, share some recommendations to keep Poa at bay in lawns.

Mowing matters

Poa’s biggest strength is that it produces lots of seed that matures quickly at any mowing height, unlike most other turfgrass species, Hathaway says. For lawns with splotches of Poa, Heydinger advises raising mowing heights to build the health of the desirable turf so it outcompetes the Poa. For lawns with a more extensive infestation, he suggests applying glyphosate and completely renovating the turf.

Timing is important

Use a preemergent herbicide to kill many of the germinated seedlings, but make these applications before Poa is germinating, which mostly occurs in the fall, Hathaway says.

Rotate products to avoid herbicide resistance

For cool-season grasses, Hathaway recommends post­emergent herbicides, such as ethofumesate (apply in late fall), amicarbazone (spring) and mesotrione. In warm-season grasses, Mosdell suggests atrazine and simazine for preemergent and postemergent control and prodiamine as a preemergent in late summer/early fall. Trifloxysulfuron-sodium is an effective postemergent, depending on turf type.

One application isn’t enough

Hathaway says that when using these products, make sure the Poa is actively growing (not in the middle of a hot summer), and LCOs must make more than one application in the same season to get good control. Poa can’t be allowed to completely recover between applications, so keep the intervals at no more than 21 days apart.

Look beyond herbicides

Plant growth regulators (PGRs) are another option. Some PGRs will regulate Poa growth to give the other species the ability to outcompete it over many seasons, Hathaway says. Heydinger adds that a lawn might see a reduction in Poa with PGR use, but it will take a number of applications, and that PGR treatment is more effective in monocultures of turf.