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quackgrass (Agropyron repens)
ODA rating: B
Perennial; grows 1 to 3 feet tall. Leaf blades 1/4 to 1/2 in wide, flat, pointed and often constricted near the tip. Flower spikelets arranged in two long rows, borne flatwise to the stem. Rhizomes yellowish white, sharp pointed, somewhat fleshy, and able to penetrate hard surfaces and tubers and roots of other plants. 
Quackgrass rhizomes produce a chemical that can suppress the growth of other plants and adversely affects the yield of all cultivated crops. It is often a contaminant of cultivated seed, which results in grade reduction. In severely infested fields, quackgrass rhizomes can weigh as much as 7 to 9 tons/acre.

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Images courtesy of Weed Science Society of America.
Introduced from the Mediterranean area, it has spread over much of North America.
The first documented site in Oregon was 1902 in Clackamas County.

Map legend
Yellow:  limited distribution
Red:     abundant
Grey:    not known to be present
Biological controls
No approved biological control agent is available.