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Weeds and Their Control: Cocklebur (Xanthium pennsylvanicum)

Cocklebur is an annual native to Europe and Asia but now found throughout the United States. The plants like rich, fertile soil with at least half day of sun and are common weeds in gardens, fields, nurseries, crop land, and roadsides. The seeds and seedlings are poisonous to livestock and can even cause death but the toxicity of the plants decreases quickly after the first true leaves appear. Although mature plants are not toxic they are distasteful to animals and not eaten.

Description: Seedlings begin to appear in the spring and continue into summer. The seedling stems are purple at the base and bear large medium green leaves. As the seedling matures, erect, branched stems grow 2-6 1/2 feet high and are covered with short stiff hairs, bumps, and longitudinal ridges. The stems are green with maroon to black spots and bear alternate leaves on long petioles. The lobed leaves are 2-6” long, triangular to ovate, and have stiff hairs. Male and female flowers are produced in separate clusters on short petioles arising from the leaf axils and are green and inconspicuous. Green burs develop from the female flowers, each containing 2 seeds, one germinating the following year, the other germinating the year after. Each bur is about ½” long and is covered with hooked barbs, with two extra long ones at one end. The burs turn brown as they mature and hook onto animals as they pass by. A single plant can produce 400 seeds in a season. The root is a taproot.

Weeds and their Control Pointer Control: Young plants are easy to pull up or hoe out but as the plant matures the taproot develops and removing the plant becomes more difficult. Mature plants must be cut down well below the soil line so that new stems do not emerge. Removing the tops before the seeds ripen is essential since seed is the only method of reproduction. Large populations of cocklebur can be cut down with a weed trimmer while the burs are still green thus removing the seed source but seeds that reach the soil can remain viable for up to 16 years. Since the plant is an annual it will die at the end of the growing season.