Summer stress of Poa annua and Poa trivialis in Lawns and Sports Fields

Zac Reicher, Extension Turfgrass Specialist, Department of Agronomy, Purdue University

Poa annua (annual bluegrass) and Poa trivialis (rough bluegrass) in athletic fields and lawns are starting to show signs of stress. The signs of stress include laying over (poor mow-ability), yellowing, and thinning. Patches of these fine-bladed grasses seemingly die overnight with even a minimum of drought stress. Though these grasses may have blended in with the desired turf for the rest of the year, they become extremely obvious and offensive as they thin. They are often first detected in lawns and sport fields when they turn off-color at this time of the year. The best way to keep these grasses alive as long as possible in lawns and sports turf is to maintain adequate soil moisture. This is because these grasses are very susceptible to heat and/or drought stress. Typical fungicide programs on sports fields probably won't extend the life of these grasses and fungicides are not usually recommended on lawns. On the other hand, heat and drought stress can be used in a program to help control these grasses. Allowing an area to dry out and go dormant will kill the Poa annua and weaken the Poa trivialis. Follow this up with irrigation to encourage recovery and fill-in of the desired turf, fall fertilization, and possibly an application of preemergence herbicide near Labor Day for Poa annua (if you don't have to overseed). Much more information is available at our new publication AY-41-W: ID and Control of Annual Bluegrass and Rough Bluegrass in Lawns.