Tall White Top

Perennial Pepperweed (Lepidium latifolium)

Lepidium latifolium, known by several common names including Broadleaved Pepperweed, Pepperwort, or Peppergrass,Dittander, Dittany, and Tall Whitetop, is a perennial plant that is a member of the mustard and cabbage family.

This plant is native to southern Europe, Mediterranean countries and Asia as far east as the Himalayas. It is an introduced species in North America, where it grows throughout the United States and Mexico. It may have been introduced to the United States when its seed got into a shipment of sugar beet seeds.

Perennial Pepperweed (Tall White Top)
Perennial Pepperweed (Tall White Top)

L. latifolium normally grows to between 11 and 38 inches, but may grow as tall as 76 inches. The plants have numerous woody stems, alternating waxy leaves and clusters of small, white flowers. It produces small (1.6 millimeter) fruits which each contain two reddish seeds. It has an extensive root network, known to reach 9 feet in depth and constitute 40% of the total biomass of the plant.

Dried stems of L. latifolium are sometimes used in flower arrangements.

The plant is most invasive in wetland habitat, including riparian zone; from there it easily spreads to other ecosystems, such as sagebrush.

It can be spotted most easily by the untrained eye along the Truckee River near Tracy-Clark, growing in the riparian areas along the River, next to the Freeway.  In the Truckee and Carson Divisions of the Newlands Project it can be found not only next to Irrigation Canals, Ditches, and Drains, but also on Fields, Parks, and around Private Residences.

Mechanical Control

In agricultural weed control, mechanical treatment is usually the first option for suppression of pests. The riparian wetland areas where perennial pepperweed is becoming established are not suited by topography, rock cover and/or woody vegetation for mechanical control. Most native hay meadows have never been plowed. The nature of perennial pepperweed’s creeping root system negates most mechanical control measures. It is nearly impossible to cut the roots fine enough to prevent the sprouting of buds that form new plants.

Sprouts from root segments grow very rapidly, often resulting in flowering plants in the same year that the parent roots are cut in tillage operations. Mechanically cut roots are very resistant to drying. Roots exposed on the soil surface over winter will sprout the next spring. The crowns of established plants become enlarged and very woody.

Mowing

Some farmers believe repeated mowing can suppress perennial pepperweed. This form of control should not be dismissed without further trials, but mowing has to be very frequent with a very short stubble height for any chance of success in controlling this species. For most sites where it is established, such treatments are not practical. As we will expand upon later, mowing to remove the old accumulations of woody stems is a necessity before grazing or most herbicidal treatments can be applied.

Grazing

Once stem elongation begins, most herbivores will not consume the herbage of perennial pepperweed under any conditions. The only chance for herbivory is in the early spring when the leaves are just emerging. In order to obtain grazing utilization at this time, it is necessary to mechanically remove the previous years’ accumulation of woody stems. In certain situations, such as extremely salt affected meadows, we have observed utilization of perennial pepperweed shoots by livestock.  There have been repeated, unverified reports that perennial pepperweed is poisonous to horses. The poisoning reportedly occurred with animals under confinement being fed hay contaminated with perennial pepperweed.

Chemical Treatments:

A number of chemical control measures have been found effective when properly applied and preparation of the area has been exercised prior to application of the herbicide.

  • DRY AREAS:  rangelands, roadsides, native hay meadows when seasonally dry, and dry upland areas.
  • 2, 4-D: (Examples of Name Brands are; Weedone 638, and Weed-B-Gone)

Application rate is based on strength of active ingredient, but is recommended at 2 pounds per acre.  Read application instructions on packaging.

Best application for 2,4-D is at bud to early bloom stage.

Note:  Use the Amine form of 2,4-D.  It is cheaper and as effective as other forms.  Multiple applications per year can be effective.

  • Chlorsulfuron:  (Examples of Name Brands are: Telar)

Application rate of 0.75 to 1.5 ounces per acre.

Best application for Chlorsulfuron is at bud to early bloom stage.  Product is very toxic to broadleaf plants such as flowers, vegetables, and alfalfa.

  • Metsulfuron:  (Examples of Name Brands are: Escort)

Application rate  of .75 to 1 ounce per acre.

Best application is at bud to early bloom stage.  Product is very toxic to broadleaf plants such as flowers, vegetables, and alfalfa.

May be used prior to grazing with no waiting period.

  • Imazapyr:  (Examples of Name Brands are: Arsenal)

Application rate is dependant on strength.  0.75 to 1.5 ounces per gallon at 1.5 to 3 pints per acre.  

Best application is at bud to early bloom stage.  Provides bareground control sutible for roadsides.

  • WET SITES: (includes riparian area, wetlands, ditchbanks, irrigated agriculture)
  • 2,4-D (labeled for use next to water)  (Examples of Brands are: Weedar 64 and Armine 4)

Application rate: up to 2 lbs or if liquid under the included brand names; 2 quarts per acre.

Spray at bud to early bloom stage; when using a wipe applicator, apply when plants are knee height or shorter.

  • Glyphosate: (labeled for use next to water) (Examples of Brands are: Rodeo)

Application rate: 3.0 lbs per acre or .75 gallons for acre.  

Mow plants at bud to early bloom stage, allow plants to regrow to bud/early bloom stage, then apply glyphosate.  This method has not been tested in Nevada, but is effective in other States.

  • SPOT SPRAYING:
  • 2,4-D:  (Examples of Brands are: Weedar 64 and Armine 4)

Application rate: Always follow label directions.  1 ½ to 2 teaspoons per gallon of water at 2 to 3 pints per acre.

Best application for 2,4-D is at bud to early bloom stage.

Note:  Use the Amine form of 2,4-D.  It is cheaper and as effective as other forms.  Multiple applications per year can be effective.

  • Glyphosate: (Examples of Brands are: Rodeo)

Application rate:  Always follow label directions. 1.5 to 2.5 ounces per gallon and 4.5 to 7.5 pints per acre.

Mow plants at bud to early bloom stage, allow plants to regrow to bud/early bloom stage, then apply glyphosate.  This method has not been tested in Nevada, but is effective in other States.

  • Metsulfuron: (Examples of Brands are: Escort)

Application rate:  1.3 grams to 3 gallons of water, and follow label direction for spot application.

Apply at bud flowering stage.  Add 1 Tsp (3ml) of household ammonia to 3 gallons.  This mixture is stable for 3 days.  Only mix for area needed and do not store.

  • Disclaimer:

Although care has been taken to ensure the accuracy, completeness and reliability of the information provided, Truckee-Carson Irrigation District (TCID) assumes no responsibility therefore.  The user of the information agrees that the information is subject to change without notice. TCID assumes no responsibility for the consequences of use of such information, nor for any infringement of third party intellectual property rights which may result from its use.

IN NO EVENT SHALL TCID BE LIABLE FOR ANY DIRECT, INDIRECT, SPECIAL OR INCIDENTAL DAMAGE RESULTING FROM, ARISING OUT OF OR IN CONNECTION WITH THE USE OF THIS INFORMATION.