Annual Bluegrass
This grassy weed (also called wintergrass, poa annua, speargrass) is capable of growing at mowing heights lower than 1/4". It thrives in cool, moist weather or damp, shaded locations. It produces hundreds of whitish green seed heads at any mowing height. Because of its tolerance of close mowing and seed head formation, it is particularly troublesome on golf greens.
Their typical "boat-shaped" leaf tips, which curve up like the bow of a boat, are a distinguishing characteristic of the genus.
Tends to grow in small clumps and seldom reaches heights greater than 10 inches. The seeds appear delicate with no noticeable hairs.
Annual bluegrass summary:
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Winter annual or biennial
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Reproduces by seed and stolons that root at nodes
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Annual bluegrass forms fibrous roots and can grow up to 15" tall if left un-mown
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Leaves are apple green 1/2" - 3/4" long
- Annual bluegrass occurs on wet, compacted soils and in cool temperatures
Efforts to find chemical controls for Poa have been thwarted by its diverse genetic make-up. Poa is officially described as a cool-season winter annual. Winter annuals are plants that germinate in late summer to early-fall, overwinter, and produce seed in the spring. Typical winter annuals die soon after seed production as daytime air temperatures increase.
There seems to be a link between traffic and annual bluegrass pressure. Mowing height and soil compaction are often associated with increasing annual bluegrass infestations. Some believe limiting irrigation can produce additional stress on annual bluegrass helping to expose it to summer disease pressure.