Annual Bluegrass
This grassy weed (also called wintergrass, poa annua, speargrass) is capable of growing at mowing heights as low as 1/4". It thrives in cool, moist weather even in damp, shaded areas. It produces hundreds of whitish green seed heads at any mowing height. Because of its tolerance to close mowing and seed head formation, it is especially difficult to control.
Annual bluegrass has "boat-shaped" leaf tips that curve up like the bow of a boat. It tends to grow in small clumps and seldom reaches heights over 10".
Annual bluegrass summary:
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Winter annual or biennial
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Reproduces by seed and stolons that root at the nodes
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Leaves are about 1/2" - 3/4" long
- Annual bluegrass occurs on wet, compacted soils and in cool temperatures
Efforts to find chemical controls for annual bluegrass have been thwarted by its diverse genetic make-up. It 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.