Q: How do I control annual bluegrass?
A: The annual nature of this weed supplies its most noxious habit: it re-seeds itself prolifically! Annual bluegrass is outwardly attractive in the winter but just wait until spring! The thick mat of bluegrass chokes out the better turf underneath.
The old-timers call this one “po anner” due to its scientific name: Poa annua. That name immediately tells us that this grassy plant is an annual.
Every blade (of which there are thousands) seems to be covered with seeds. These seed are carried by animals, water and lawnmowers to other parts of the lawn. When hot weather comes, the bluegrass dies, leaving a large bare spot and a legacy of thousands of seed for next fall.
The best control for annual bluegrass is to apply a pre-emergent weed chemical in the fall. The best time is usually in mid-September. Any pre-emergent product that controls crabgrass will control annual bluegrass.
All of the following products give excellent control of bluegrass:
benefin (Amaze, Balan, Crabgrass Preventer)
pendimethalin (Halts, LESCO)
The pre-emergent will prevent seeds from germinating. Of course, the pre-emergent can not be used on a fescue lawn which you intend to re-seed!
If bluegrass is present in winter/early spring lawns, imazaquin (Image for Nutgrass) is labeled for use on all grasses except fescue. Since Image must be absorbed by roots, control may not be evident for several weeks.
For faster control in dormant bermudagrass only, spray bluegrass patches lightly with glyphosate (Roundup etc.) Make sure bermudagrass is truly dormant before spraying and spray lightly.
NOTE: Bermudagrass is only dormant when temperatures have been in the low 20′s for a week or more.
Another, safer, method for control is to wrap an old towel around the tines of a yard rake and dampen it with diluted glyphosate. Using the rake like a paintbrush, apply chemical to the “bad” grass blades without harming the “good” grass.
THE SAME PROCESS OF WIPING GLYPHOSATE ONTO GREEN WEEDS CAN BE USED ON ANY UNWANTED PLANT IN A BERMUDA OR ZOYSIA LAWN: FESCUE, CHICKWEED, HENBIT, ETC.
annual bluegrass in fescue
hundreds of seeds on each plant