Cleavers
(Galium aparine)

Overview

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Cleavers is an aggressive weed that is one of the greatest concerns to canola growers due to its competitiveness and growing habits. For example, this weed has the ability to attach to the canola plant which can make harvesting very difficult. It is also problematic in crops such as wheat, corn and other cereal crops. Cleavers are annual climbing weeds that are commonly found and widely distributed in crop lands throughout Canada.

Main description

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Seedling
The cotyledon has a distinct oval shape. First leaves typically appear in a whorl, which is a distinctive morphological characteristic of this weed. 

Mature plant
This annual climbing weed has square stems covered in bristly hairs that aid in attachment to other vegetation. Plants exhibit prostrate growth with branching. Leaves grow as whorls of 6-8 and have tiny hairs on them that are bristly and tough. Cleavers start to flower in early spring resulting in small white quaternary flowers with four sepals that appear in cluster of 3-9. At full maturity, Cleavers can reach a size up to 120-180 cm.

Propagation
An individual cleaver plant can produce 3,500 seeds, which resemble canola seeds. This makes the separation between both types of seed extremely difficult. The seeds can remain viable for 1-3 years. It is easily spread by harvesting equipment and in contaminated soil or manure. The bristly seeds cling to the hair and wool of animals and to clothing. Cleavers are well known for their ability to germinate throughout the growing season. 

Optimal growth conditions

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Seed germination can occur over a larger range of temperature, ranging below 5 degrees Celsius to greater than 20 degrees Celsius. The species, Galium aparine, occurs in a variety of habitats, from sea level to mid-elevations in the mountains. It can also be found growing in very wet fields and field clearings. Due to the increased use of direct seeding in Western Canada, winter annual cleavers are becoming more abundant.