THE BIOLOGY OF CANADIAN WEEDS.: 37 Poa annua L.

A summary of biological information is provided on Poa annua L. (annual blue grass), which is common throughout the temperate regions of the world as a weed of cultivated and wasteground habitats. The distribution of distinct erect-annual and prostrate-perennial variants of the species is highly correlated with habitat type, with the latter predominating in closely mowed turf and the former in open fields, wasteground, etc. Poa annua is a serious weed in turfgrass. It is found on most soil types and exhibits a high tolerance to trampling, mowing and poorly aerated soils. The species, however, lacks tolerance of strongly acid soils, high pollution levels and extremes of temperature and moisture. The species is fully self-compatible and is predominantly selfing. Seed production and seed viability are generally high. Factors affecting seed germination are summarized; these include response to: temperature, moisture, O 2 partial pressure, light, cultivation practises, fertilizers, pH and the environmental conditions under which the parent plant was grown. Selective herbicide control of established annual blue grass is difficult. Present postemergence herbicides include endothal and linuron. Differential herbicide response in P. annua has been recorded for endothal, metoxuron and atrazine.