Perennial peppergrass or Tall whitetop or Perennial pepperweed [Lepidium latifolium L.][LEPLA][CalEPPC: A1][CDFA list: B] Photographs Map of Distribution


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[
SYNONYMS] [GENERAL DESCRIPTION] [SEEDLINGS] [MATURE PLANT] [ROOTS and UNDERGROUND STRUCTURES] [FLOWERS] [FRUITS and SEEDS] [POSTSENESCENCE CHARACTERISTICS] [HABITAT] [DISTRIBUTION] [PROPAGATION/PHENOLOGY] [MANAGEMENT FAVORING/DISCOURAGING SURVIVAL] [SIMILAR SPECIES] [CONTROL METHODS]


SYNONYMS: perennial peppergrass or peppercress, slender perennial peppercress, broadleaved or broadleaf pepperweed, tall whitetop, giant white weed, iron weed, Cardaria latifolia (L.) Spach

GENERAL DESCRIPTION: Erect noxious perennial to 2 m tall, with white flowers and extensively creeping roots. Plants are highly competitive and typically form dense colonies that displace native vegetation and wildlife. Toxicity to grazing livestock is undocumented. Goats appear to tolerate heavy consumption of fresh plants. However, there have been reports of horses becoming ill after being fed contaminated hay. Perennial pepperweed has spread rapidly throughout the western U.S. since its introduction from Eurasia around 1936. Outside of California, it is a major problem in Nevada.

SEEDLINGS: Cotyledons obovate to oblong, ~ 3-8 mm long, glabrous, tip rounded, base tapered into a short stalk ~ 2-3 mm long. First leaves developmentally alternate, but appear opposite, ovate to oblong, ~ 4-12 mm long, glabrous, tip +/- rounded, base +/- wedge-shaped, on a stalk ~ 5 mm long. Margins entire to slightly wavy. Subsequent leaves resemble first leaves and are increasingly larger.

MATURE PLANT: Crown and lower stems +/- weakly woody. Foliage glabrous, green to gray-green. Leaves alternate, lanceolate to elliptic or oblong. Basal leaves to 30 cm long and 8 cm wide, with serrate margins and on long stalks (~ 3-15 cm long). Stem leaves reduced, +/- sessile, tapered at the base, margins entire to weakly serrate.

ROOTS and UNDERGROUND STRUCTURES: Roots long, thick, minimally branched, vigorously creeping. Most roots occur in the top 60 cm of soil, but some can penetrate to depths of 3 m (10 ft) or more. Carbohydrate reserves are lowest when flowering stems are elongating (bolting stage).

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FLOWERS: May-September. Inflorescences +/- pyramidal to rounded on top. Petals 4, white, spoon-shaped, ~ 1.5 mm long. Sepals oval, less than 1 mm long, +/- covered with long simple hairs. Stamens 6, 4 long, 2 short. Insect-pollinated.

FRUITS and SEEDS: Pods (silicles) 2-chambered, round to slightly ovate, slightly flattened, lacking a notch at the apex, ~ 2 mm long, +/- covered with long simple hairs. Stigma sessile, persistent. Stalks much longer than pods, glabrous or sparsely pubescent. Seeds ellipsoid, slightly flattened, +/- 1 mm long, 0.5 mm wide, reddish-brown, with a shallow groove on each side and minutely granular surface. Seeds fall from pods irregularly through winter and some may remain in pods until the following season.

POSTSENESCENCE CHARACTERISTICS: Above ground parts typically die in late fall and winter. The pale tan dead stems persist for more than one year.

HABITAT: Wetlands, riparian areas, meadows, salt marshes, flood plains, beaches, roadsides, irrigation ditches, agronomic crops, especially alfalfa, orchards, vineyards, irrigated pastures, ornamental plantings. Typically grows on moist or seasonally wet sites. Tolerates saline and alkaline conditions.

DISTRIBUTION: Throughout California, except deserts and northern North Coast and adjacent mountains (Del Norte, Humboldt, n Mendocino cos.); to Canada, Montana, Indiana, Texas. Also, regions of the Northeastern U.S. To ~ 2000 m (6500 ft).

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PROPAGATION/PHENOLOGY: Reproduces vegetatively from creeping roots and root fragments and by seed. Roots do not hold soil together very well, allowing erosion of river, stream, or ditch banks.Root fragments and seeds float and disperse with flooding, soil movement, and agricultural and other human activities. Seeds can also cling to tires, shoes, and the feet, fur, and feathers of animals and contaminate hay or crop and pasture seed. Large fragments can survive extreme desiccation on the soil surface for extended periods. Fragments as small as 1-2 cm long and 2-8 mm in diameter can develop into new plants. New shoots begin to grow from roots in late winter. Fluctuating temperatures appear to stimulate seed germination. Plants usually produce abundant, often highly viable seed, but seedlings are seldom detected in the field. In wet years, seed production is sometimes limited by white rust (Albugo sp.) infection. Seedlings emerge mid-winter through mid-spring.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Heavy infestations are difficult to control. Cleaning agricultural or earth-moving machinery after use in infested areas and curtailing movement or use of soil, hay, and crop or pasture seed contaminated with perennial pepperweed root fragments and/or seed and can help prevent new infestations. Single techniques, such as repeated mowing, hand-digging, cultivation, grazing, and burning, typically do not adequately control perennial pepperweed. In addition, cultivation may increase infestations by dispersing root fragments. Field observations suggest that plants may not tolerate an extended period of flooding during the growing season.

SIMILAR SPECIES: Hoary cress [Cardaria draba (L.) Desv.], lens-podded whitetop [Cardaria chalepensis (L.) Hand.-Mazz.], and hairy whitetop [Cardaria pubescens (C. Meyer) Jarmol.] are noxious perennials with creeping roots that resemble perennial pepperweed. Field pepperweed [Lepidium campestre (L.) R.Br.] and clasping pepperweed [Lepidium perfoliatum L.] are related annual/biennials. Unlike perennial pepperweed, all of these species grow only to ~ 0.5 m tall and have stem leaves with lobed bases that clasp the stems and foliage +/- covered with short hairs. In addition, Cardaria species typically have inflated pods greater than 2 mm long with persistent styles 1-2 mm long. Field pepperweed and clasping pepperweed do not grow in dense colonies.

CONTROL METHODS:

An excellent summary of biology, ecology and control information for perennial pepperweed (Leaflet #02-1; January 2002) has been produced by Mark Renz, Carl Bell, Cheryl Wilen, and Joseph M. DiTomaso through the University of California Cooperative Extension. The information can be accessed via the world wide web at the following address: http://wric.ucdavis.edu/information/pepperweed.html

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