Perennial Pepperweed, AKA giant whitetop (Lepidium latifolium L.)
Perennial pepperweed is an aggressive herbaceous perennial that spreads through both seed and an extensive root system. It produces multiple erect stems from a semi-woody crown and typically grows 2–4 feet tall. Stems may branch near the upper portions of the plant.
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Basal leaves are 4–12 inches long, have petioles (leaf stalks), and may be slightly toothed. Stem leaves are alternately arranged, hairless, and directly attached to the stem. They are narrow, up to 12 inches long and 1–2 inches wide, and often resemble willow leaves. A distinct white midvein is usually visible. Leaf margins are smooth to slightly toothed.
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Flowering occurs from late spring through late summer. Small white flowers with four petals form in dense, rounded clusters at the ends of stems, giving the plant a conspicuous white appearance when in bloom.
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Perennial pepperweed has a deep taproot along with creeping lateral roots that allow it to spread and form dense colonies. Seeds develop in small capsules and are flattened, reddish-brown, and numerous.
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This species is commonly found in riparian areas, wetlands, roadsides, and disturbed sites, where it can displace native vegetation and reduce habitat quality.
Quick ID Guide
Life Cycle:
• Herbaceous perennial
• Semi-woody crown
• Deep taproot and creeping lateral roots
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Height:
• 2–4 feet tall
• Multiple erect stems
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Leaves:
• Alternate arrangement
• Narrow, willow-like shape
• Hairless
• Distinct white midvein
• Smooth to slightly toothed margins
• Up to 12 inches long
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Flowers (Late Spring–Late Summer):
• Small, white
• 4 petals
• Dense clusters at stem tips
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Seeds:
• Small capsules
• Flattened
• Reddish-brown
Management Options
Prevention and cultural control practices are critical. Clean, Drain, and Dry all watercraft — including rafts and paddleboards — before moving between waterways to prevent the spread of perennial pepperweed into new riparian areas.
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There are currently no approved biological control agents for perennial pepperweed.
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Small infestations may be controlled through careful hand pulling or digging, ensuring that the entire taproot and all lateral roots are removed. Extreme care must be taken, as root fragments can resprout. Tillage is strongly discouraged because it can fragment and spread reproductive roots. Grazing may help reduce seed production, but it will not eliminate the root system.
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For larger infestations or where manual removal is impractical, herbicide applications are recommended. Spring treatments can prevent flowering and seed production, while fall applications may be more effective in targeting the root system. Always read and follow the herbicide label before use. Contact Sublette County Weed & Pest for guidance on product selection, rates, and application timing.
