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spikeweed(Hemizonia pungens)
ODA rating: B
 
USDA Symbol: HEPU5
Oregon spikeweed distribution
 
Other common names
common tarweed and maritime spikeweed
 
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Images courtesy of Oregon Department of Agriculture.
 
 
If images are downloaded and used from the ODA web site please be sure to credit the photographer.
 
Description
Spikeweed is annual that blooms July to September. This plant grows 1 1/2 to 3 feet tall and has basal leaves that are pale, straw colored, stiff and several inches long with narrow lobes. Stem leaves 1/2 inch long or less and sharp pointed, bearing dwarf stems in their axils. Flower heads yellow, 1/3 inch broad and borne at the tips of short leafy branches.
 
Impacts
Occurs on roadsides, waste areas and in low alkaline sites of grain fields and rangelands. Spikeweed is a tough, spiny plant which is avoided by livestock. It is a heavy seed producer and forms dense stands on areas favorable to its growth.
 
Introduction
Spikeweed is native to California. It was introduced to the Columbia river basin of northeastern Oregon and southeastern Washington within the last century and behaves as an invasive weed and agricultural pest. It is reported more frequently in central and eastern Oregon, occurring on roadsides, waste areas and in low alkaline sites of grain fields and rangelands.
 
Distribution in Oregon

Biological controls
No approved biological control agent is available.