Biology and Management of Biennial Wormwood
Biology and Management of Biennial Wormwood
Biology and Management of Biennial Wormwood
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<strong>Biology</strong> <strong>and</strong> <strong>Management</strong> <strong>of</strong> <strong>Biennial</strong> <strong>Wormwood</strong>Identifi cation<strong>Biennial</strong> wormwood is a small-seeded plant that behaves like an annualspecies. <strong>Biennial</strong> wormwood stems arise from a tap root, are hairless <strong>and</strong><strong>of</strong>ten are tinged red. The leaves are hairless <strong>and</strong> have toothed margins. Plantstypically grow 3 to 7 feet (1 to 2 meters) tall with a woody stem averaging1 to 2 inches (3 to 5 centimeters) in diameter. <strong>Biennial</strong> wormwood flowersconsist <strong>of</strong> heads in clusters arranged in a spikelike form. <strong>Biennial</strong> wormwoodis a prolific weed, producing approximately 1 million seeds per plant(Stevens 1932). Mahoney <strong>and</strong> Kegode (2004) later estimated that a singlebiennial wormwood plant produced 400,000 seeds. Stevens’ estimate <strong>of</strong> seedproduction possibly was from a biennial plant, whereas the later estimate wasfrom an annual plant.Figure 3. Bolting biennial wormwood plant.Figure 4. Photo showing spikelike flower head <strong>of</strong> a mature biennialwormwood plant in early September (left) <strong>and</strong> mid-October (right) atFargo, N.D.3
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