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STAND LOSS AND WEED ENCROACHMENT IN PERENNIAL GRASS SEED CROPS

G. W. Mueller-Warrant

USDA-ARS, Natl.  For.  Seed Prod.  Res.  Center, 3450 SW Campus Way

Corvallis, OR, 97331-7102, USA.

Annual bluegrass (Poa annua) is an opportunistic weed in perennial ryegrass (Lolium perenne) grown for seed, relying on thin crop stands to proliferate.  Poor post-harvest regrowth and damage from weed control treatments are primary factors that thin L. perenne stands.  Maximum L. perenne yield loss in dense P. annua stands averaged 45%.  Downy brome (Bromus tectorum), an invasive weed in Kentucky bluegrass (Poa pratensis) grown for seed, weakens and destroys stands through intense competition.  Complete P. pratensis yield loss occurred at about 200 B. tectorum per M².  In L. perenne, crop safety must be emphasized when selecting treatments to control or suppress P. annua.  In P. pratensis, control of B. tectorum must be maximized, and crop safety is a secondary concern.

Keywords: Residue management; full straw load chop; vacuum sweep