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A WEED REPORT from the book Weed Control in Natural Areas in the Western United States
<br /> This WEED REPORT does not constitute a formal recommendation.When using herbicides always read the label,and when in
<br /> doubt consult your farm advisor or county agent.
<br /> This WEED REPORT is an excerpt from the book Weed Control in Natural Areas in the Western United States and is available
<br /> wholesale through the UC Weed Research&Information Center(wric.ucdavis.edu)or retail through the Western Society of
<br /> Weed Science(wsweedscience.org)or the California invasive Species Council(cal-ipc.org).
<br /> Lepidium latifolium L.
<br /> Perennial pepperweed (tall
<br /> whitetop) ,.
<br /> Family:Brassicaceae -,. �•
<br /> Range:All western states,except North and South Dakota. .
<br /> Habitat:Many different areas and habitats,including wetlands,
<br /> riparian areas,meadows,vernal pools,salt marshes,flood
<br /> plains,sand dunes,roadsides,irrigation ditches,ornamental
<br /> plantings,and agronomic crops,including alfalfa,orchards,
<br /> vineyards,and irrigated pastures.Most typically found on moist or seasonally wet sites in the west,and most
<br /> problematic in riparian or wetland areas.Tolerates saline and alkaline conditions.
<br /> Origin:Native to Eurasia.
<br /> Impacts:Perennial pepperweed can rapidly form large,dense stands that displace desirable vegetation and
<br /> wildlife.Populations easily spread along waterways and can infest entire stream corridors,riparian areas,or
<br /> irrigation structures.Roots do not hold soil together well,allowing erosion of river,stream,or ditch banks.
<br /> Flopded streams often wash away roots growing along the streambank,and new infestations develop
<br /> downstream.Once established,perennial pepperweed is persistent and difficult to control in crops,natural
<br /> areas,and ornamental plantings.Perennial pepperweed reduces forage quality in hay and pasture.Perennial
<br /> pepperweed plants extract salts from deep soil and deposit them on the soil surface,inhibiting the germination
<br /> and growth of other species that are sensitive to salinity.
<br /> Western states listed as Noxious Weed:California,Colorado,Idaho,Montana,New Mexico,Oregon,South
<br /> Dakota,Utah,Washington,Wyoming
<br /> California Invasive Plant Council (Cal-IPC)Inventory:High Invasiveness
<br /> Perennial pepperweed is an erect perennial to 6 ft tall.The crown and lower stems are weakly woody.The
<br /> foliage lacks hairs and is green to gray-green,often dusted with powdery white caused by a rust fungus.The
<br /> basal leaves are larger and wider than stem leaves,to 1 ft long and 4 inches wide,with serrate margins.The
<br /> aboveground parts typically die in late fall and winter,leaving dead stems and thatch which can persist for
<br /> several years.The roots are long,thick,minimally branched,and vigorously creeping.Most grow in the top 2 ft
<br /> of soil,but some can penetrate to a depth of 10 ft or more.
<br /> The inflorescences are rounded to pyramidal and consist of numerous small white flowers.The flowers
<br /> have four petals,producing small pods(about 2 mm long)with tiny reddish-brown seeds(about 1 mm long).
<br /> Perennial pepperweed is a prolific seed producer.Laboratory tests suggest seeds germinate readily with
<br /> fluctuating temperatures and adequate moisture;however,seeds do not appear to remain viable in the soil for
<br /> extended periods.As a result,perennial pepperweed reproduces primarily vegetatively from roots and root
<br /> fragments.Large root fragments can survive desiccation on the soil surface for extended periods,and
<br /> fragments as small as 0.5 to 1 inch long and 2 to 8 mm in diameter can develop into new plants.Root fragments
<br /> and seeds disperse with flooding,soil movement,and human and animal activities.
<br /> NON-CHEMICAL CONTROL
<br /> Mechanical Seedlings are easily controlled by hand-pulling or tillage,but these techniques do not control established
<br /> (pulling,cutting, plants because shoots quickly resprout from vast root reserves.In addition,seedlings are not often
<br /> disking) encountered.Root segments as small as 1 inch are capable of producing new shoots.Cultivation and tillage
<br /> typically increase infestations by dispersing root fragments.Clean equipment after tillage to prevent
<br /> spreading root fragments.
<br /> Mowing stimulates perennial pepperweed plants to resprout and produce new growth,but mowing is
<br /> I of 3 2013
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