Overview:

An annual or winter annual that reproduces by seed only. Native to Europe, this plant has been used by herbalists and its seeds are similar to coffee when roasted. Can cause significant crop loss by out shading and interfering with harvesting equipment. It has a simple taproot. Cleavers and false cleavers are nearly identical in appearance, except that false cleavers (G. spurium) have smaller flowers and seed nutlets.

Habitat

Cleavers prefers damp to moist soils but can tolerate dry soils with shade. It grows in sandy, loam, or clay soils.

Identification:

Stems: Stems are square, trailing, and covered with short, bristly spines giving them a 'sticky' feel. They can grow 1 to 2 m in length and climb other plants for support. The stems will climb or twine around other plants to reach sunlight. They are usually profusely branched.
Leaves: Leaves are lance-shaped, have smooth edges and pointed tips, and grow 1 to 4 cm long. Leaves occur in whorls of 6-8 and have short bristly spines along their edges and midribs.
Flowers: Flowers are very small and plain, white to greenish, and have 4 petals. They are borne on short stalks emerging from the upper leaf axils. Flowers are hermaphroditic – having both male and female organs – and are self-pollinating.
Seed: Seed are gray-brown nutlets, about 2 mm long, covered with short, bristly spines, and are produced in pairs. Seeds must be covered by soil to germinate and viability is limited to about 2-3 years.

Prevention:

Seeds are a similar size to some crop seeds, such as canola, and are difficult to separate, therefore contaminated crop seed is one method of spread. A single plant can produce over 1000 seeds which can survive ingestion by livestock and birds. Seeds will float on water and can also be spread in manure.

Control:

Grazing: Not a control option as the sticky seeds are easily spread by animals.
Cultivation: Tillage can promote germination by burying surface seed to depths more suitable for germination, and seed can be transported on equipment. Repeated, shallow tillage followed by herbicide application on new plants could exhaust the seed bank – equipment must be cleaned after.
Mechanical: Mowing is not effective. Small infestations can be hand-pulled and left in the sun to dry. Plant debris can then be burned, or bagged and put in landfill-bound garbage.
Chemical: Bentazon, Bromoxynil, Dicamba, Ethalfluralin, Florasulam, Fluroxypyr, Glufosinate ammonium, Glyphosate, Imazamox, Linuron, MCPA, Mecoprop-p, Pyroxsulam, Quinclorac, and Tribenuron-methyl (in a product mix with thifensulfuron-methyl) are registered for use on cleavers. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.
Biological: A European gall mite has been screened and approved for release in Canada. No overwintering survival of the agents was observed during field trials in Alberta. (McClay, Alec. 2005)

 

Selected Images

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Maps

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Invasive Listing Sources

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• Pacific Northwest Exotic Pest Plant Council, 1998

References

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Common Name Reference: Weed Science Society of America Common Names List

Scientific Name Reference: USDA, NRCS. 2010. The PLANTS Database. National Plant Data Center, Baton Rouge, LA, USA.