Description:

PERENNIAL PEPPERWEED — Lepidium latifolium L.

Brassicaceae — (Mustard family)

Perennial pepperweed is similar to whitetop, however, it is taller. Perennial pepperweed stands one to over three feet high with a heavy, sometimes woody, crown. The leaves lanceolate, bright green to gray-green, the lower leaves are oblong with toothed margins and a waxy texture, basal leaves larger than upper leaves; inflorescence a raceme. The upper leaves do not clasp the stem as whitetop does. Flowers are white, in dense clusters near ends of branches, very small; fruit a silicle; seeds two per fruit, rounded, flattened, slightly hairy, about 1/16 inch long and reddish-brown. Flowering occurs from early summer to fall. 

Perennial pepperweed is a native of Southern Europe and Western Asia but is now found in many parts of the United States. It has been declared noxious in a number of Western states. The deep-rooted perennial plant with extensive, vigorous creeping root system reproduces by  root stalks and also by seed.  Perennial pepperweed grows in waste places, riparian areas, ditches, roadsides, pastures, cropland and disturbed areas.  The waxy layer makes this perennial difficult to control.

Nonstandard name: broad-leaved peppergrass, tall whitetop, Virginia pepperweed.

Growth Habit: Erect perennial, numerous stems, spreading by seed and deep-seated rootstocks.

Leaves: Alternate, lance shaped, bright green to gray-green, waxy, smooth to toothed margins, basal leaves larger than upper leaves.

Stems: Branched, smooth, waxy, 1-3 feet tall.

Flower: Raceme of small white flowers in dense clusters near branch ends.

Roots: Deep-seated and spreading.

Seeds: Small, rounded, flattened, slightly hairy, 1/16 inch long, reddish brown.

Other: Deep roots make it difficult to control.

(Courtesy of Weeds of the West)

Control Strategies:

Perennial Pepperweed is very hard to control using cultural practices. The stored energy in the roots will insure that it can still produce competitive stands after three years of clean cultivation. 2,4-D is moderately effective if used twice a year. The first treatment needs to occur prior to blooming when the plants are only a few inches tall. Most of the time we are too late to get the best results with 2,4-D.  There are two much more effective herbicides, Telar and Escort. They can be applied at any time the plant is green, so that extends the window of opportunity. Small amounts of these herbicides provide 95% or better control from a single application. Escort and Telar can be applied at the rate of 0.75 to 1.0 ounces per acre. The lower rate is safer on grasses growing under droughty conditions. Escort is very hot on most shrubs and trees, so there can be considerable collateral damage from drift. Telar has more soil activity and a longer residual than Escort, but is safer around trees and shrubs. They cost about the same and the District cost shares on the products. Use Escort where you have crop rotation concerns as Telar can persist for several years. Both herbicides must be used with a non-ionic agricultural surfactant or with methylated seed oil at 0.5% by volume. Perennial pepperwood has a very waxy leaf surface that requires a surfactant for penetration of the herbicide.  Both Telar and Escort react with water in the spray tank, so you should use up all you mix the same day.

To learn about biological control agents for Perennial Pepperweed visit this link.