Biology:
Poa annua, is a winter annual grassy weed that is difficult to control in turf. Seeds germinate in late summer, early fall, and into spring when you will begin to see growth. Annual bluegrass is found throughout the United States, particularly in highly compacted, excessively wet soils. It has a clumping growth habit and can withstand extremely close mowing heights; thus, allowing the grassy weed to establish in home lawns and other turf, such as golf courses and sports fields.
Identification:
Annual bluegrass or poa annua, can be identified as a clump-forming grassy weed that grows in dense patches. It is generally identified by its smooth, light green leaf blades with slightly pointed, medium to long ligule, a narrow and smooth collar, and a boat-shaped leaf tip. One factor that makes annual bluegrass difficult to control is its ability to produce a large amount of seedheads. These seedheads can be observed as a greenish to white, open, pyramid-shaped panicle. These grassy weeds are annuals, meaning they live for only one season. As the temperatures climb and the weather warms up, poa annua will begin to die off, blend into the turf, and become unnoticeable.
Cultural Control:
Annual bluegrass or poa annua is a grassy weed that is difficult to control culturally. It can adapt to numerous lawn-mowing heights and the prolific production of viable seed severely limits the ability to culturally control this grassy weed.
Chemical Control:
There are options for controlling Annual bluegrass or poa annua using herbicides, however, there are no proven successful options in eliminating poa annua in spring turf. To deter germination of this weed, pre-emergent herbicides must be applied in the fall before the dormant seeds germinate. Unfortunately, these pre-emergent herbicides will inhibit germination of grass seed, rendering fall overseeding useless. To reiterate, if you want fall seeding, we cannot perform a fall pre-emergent herbicide and if you want to minimize poa Annua with a fall pre-emergent, we cannot overseed in the fall.
To keep Annual bluegrass out of your home lawn:
- Do not over-water your lawn for annual bluegrass thrives in moist areas.
- Do not compact your soil through traffic where possible and aerate your lawn, in your fall, to reduce compaction.
- Maintain dense turf through fertilization, overseeding, and weed control.
- Mow your lawn at higher heights of cut (>3 inches).
- The most successful way to rid your lawn of pao annua is to have the affected area dug out and replaced with new sod.
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