Common Knotweed (prostrate)

Pest: Common Knotweed (Polygonum arenastrum)

Pest Type: Annual broadleaf weed, short-lived perennial

Major Identifying Features: Prostrate annual, numerous slender, wiry stems that are highly branched, forms a mat, grows up to 4-8 inches, taproot can grow down to 18 inches, bluish-green leaves, narrow blades, swollen stem nodes, white-green-pinkish flowers, grows flat

Life Cycle: Winter annual/biennial, reproduces by seed, germinates in late winter or early spring, germinates in soil cracks and compacted soil, grows slowly, can form mats that are 3-4 feet in diameter, seedlings survive mowing, seeds in the soil may live long, flowers from March to October

Pest Rating: Minor

Management Rating: Easy

Host/Season/Outbreak Information: Widespread in California and grows in field crops, row crops, orchards, yards, gardens and turf, well adapted to winter and early spring rainfall

Damage Information: Troublesome in alfalfa fields where soil is compacted, it is a host for parasitic weed dodder and other pathogens such as powdery mildew, beneficial insects are attracted to flowers

Management Options: Prevention by preventing soil compaction, aeration and loosening the soil, mulching, removing weeds with weeding tools or manual removal, herbicides are usually not required even though there are many effective herbicides on the market such as benefin, dithiopyr, oryzalin, pendimethalin, prodiamine, trifluralin, herbicides are NOT recommended



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