Tips for successfully managing Poa annua in lawns

Experts say Poa annua is a difficult weed for LCOs to manage because of its ability to adapt to adverse conditions. (Photo: Nufarm)

Poa annua, also known as annual bluegrass, is a common weed that infests lawns all year round and is unsightly and hard to control. It can also develop herbicide resistance.

To help lawn care operators (LCOs) get a handle on Poa annua management, Justin Ruiz, West area manager with Quali-Pro; Ben Pease, Ph.D., turfgrass agronomist with The Andersons; Aaron Hathaway, technical services manager with Nufarm; and Jared Hoyle, Ph.D., territory manager for turf and ornamental Midwest with Corteva Agriscience, offer some tips and tricks.

Challenges to management

Poa annua is an aggressive weed that can grow in adverse conditions and produce numerous seeds even at relatively short plant heights. 

“There are always new seedlings emerging throughout the year,” says Pease. 

Hathaway says what complicates controlling Poa annua is “it is similar to desirable grass species and produces seed that can germinate immediately.”

Successful control

Experts say the best control combines good cultural practices with the proper use of herbicides. 

“Preemergent herbicides provide a barrier on top of the soil surface to prevent Poa annua seedlings from emerging,” says Hoyle.

The strategies LCOs use for Poa annua control will depend on whether their location is in the north, south or the transition zone. 

“Depending on your location, an application of preemergent herbicide during the spring season is the best approach for Poa control,” says Pease. 

He adds that postemergent applications, when used, are rarely as effective as preemergent applications.

Ruiz says plant growth regulators also can give LCOs a leg up on control.

“The use of plant growth regulators can stunt Poa annua plants and suppress seed production,” says Ruiz. 

Understanding the life cycle of Poa annua is a key to successful management, says Hoyle. He adds that the species can behave like an annual or as a perennial, depending on location. This knowledge can serve as a guide for the control of this troublesome weed.

Resistance management

Over the past decade, herbicide resistance in Poa annua has increased substantially, experts say.

“Several herbicide-resistant Poa annua biotypes occur in the U.S., and LCOs need to always be aware of this,” says Pease. 

Ruiz says the use of preemergence herbicides likely drives Poa annua resistance. Hathaway suggests LCOs rotate herbicides with different modes of action to help slow down resistance.

However, he adds that there are incidences of Poa annua biotypes resistant to more than one herbicide mode of action, which complicates the control of this weed.

“Developing a program that combines rotating herbicide modes of action with good cultural management will keep herbicide-resistant Poa annua plants in check,” says Hoyle.

Cultural controls

“Creating an environment that is not conducive for Poa annua to grow is the first line of defense,” says Ruiz. 

A healthy and robust turfgrass that is properly irrigated can help the turfgrass outcompete Poa.

“When turfgrass is healthy and properly mowed, the chemical program works better,” says Hoyle.

LCOs also should alleviate compaction with proper aeration to help the turfgrass better compete, he says. 

Finally, although fertilizer may help fertilize turfgrass, it can also bring with it, more Poa annua.

“Overfertilizing turfgrass can increase the occurrence of Poa annua,” Hoyle adds.