All plant descriptions and control methods courtesy University of Nevada Cooperative Extension
Perennial pepperweed, or tall whitetop, is a native of southern Europe and western Asia. It has naturalized in many parts of the United States, including Nevada. Many western states have declared this weed noxious. This perennial grows in waste places, wet areas, ditches, roadsides, and croplands, including alfalfa fields. It also grows in low-rainfall desert areas where its root system collects any available water. In streambeds, perennial pepperweed causes bank destabilization because of its lack of fine root hairs to hold the soil. It is a problem in hay bales because it does not cure. Its robust, spreading roots and numerous seeds make its control very difficult. Like many members of the mustard family, perennial pepperweed produces a significant percentage of hard seed with delayed germination, which ensures seeds remain viable in the soil for many years. Mechanical measures such as disking or mowing spread the plant. Chemical controls must be timed properly and applied only after last season’s dead stems and leaves are removed or the effort is wasted.
Distinguishing features:
CONTROL MEASURES
Most Effective Strategy:
Perennial pepperweed is one of the most difficult of
Nevada’s noxious weeds to control. Research
and experience have shown that the most effective treatment is a combination of
herbicides and cultural controls. Cleaning
equipment and using weed-free hay limits the number of infestations. Finding
perennial pepperweed in its first year of
establishment and initiating control efforts is the best management strategy.
Metsulfuron or chlorsulfuron are effective at killing
perennial pepperweed, but these chemicals remain active in alkaline soils for
many years, making establishment and maintenance
of competitive vegetation difficult after treatment and limiting the
effectiveness of these herbicides over the long term. If the
infestation is on highly alkaline soil, use repeated applications of 2,4-D
coupled with efforts to stimulate growth of competitive
vegetation. This may include seeding with an appropriate species and
fertilization for maximum production of the competitive
vegetation. A long-term effort over many years is required to manage an
infestation. Missing even 1 year of control severely
reduces the effectiveness of past efforts.
Mechanical Control:
Hand-pulling can be used for small infestations or where
herbicides cannot be used. It is most effective
in moist, loose soils. Pulling must be continued until no new seedlings emerge,
possibly 4 to 6 years or more. Digging, tilling,
or mowing is ineffective: such efforts encourage plants to sprout from their
crowns, perennial roots, and plant pieces.
Cultural Control:
Repeated, intensive grazing by sheep or goats may provide some
control, especially in combination with
herbicides. Maintain healthy stands of desirable plants to be competitive with
tall whitetop. Burning or bailing of last year’s
dead stems and leaves is necessary to allow herbicide applications to reach the
current year’s growing leaf surfaces.
Biological Control:
There are currently no biological controls available for
perennial pepperweed, but research is ongoing.
Read and follow the label. It is the law!
Chemical Control:
2,4-D amine or ester
Rate: Use 2 pounds a.e. per acre.
Time: Apply 2,4-D prior to bud formation. Repeated applications during the
growing season whenever green leaf material
is present (every 4 to 6 weeks). Mow perennial pepperweed at the bud stage,
remove the clippings, and allow
the plant to return to the bud stage in the late summer, then apply 2,4-D. After
a season of intense grazing, apply
2,4-D to small plants in the fall.
Remarks: 2,4-D must move into the root system to be effective. Thoroughly wet
the plant but do not over-apply the
herbicide because it will not translocate to the root.
Caution: It is not lawful to apply more than 2 pounds a.i. per acre per year.
Avoid drift to crops, especially with a volatile
ester formulation. Follow the label directions. Do not apply near or over water
unless using a product specifically
formulated for use in water.
Metsulfuron (Escort®)
Rate: Use 1 to 2 ounces per acre.
Time: Apply during the rosette to full bloom stages of growth.
Remarks: Use a nonionic surfactant to increase the herbicide’s effectiveness. In
alkaline soils, above pH 7.5, reestablishment
of competitive vegetation may be difficult due to residual herbicidal action on
germinating seedlings.
Caution: Only apply to pasture, rangeland, and noncrop sites. Follow the label
directions. Do not contaminate water.
Chlorsulfuron (Telar®)
Rate: Use 0.75 to 2 1/4 ounces per acre of chlorsulfuron (1 to 3 ounce of Telar®
per acre).
Time: Apply during preemergence or early postemergence when plants are actively
germinating or growing.
Remarks: Use a nonionic surfactant to increase the herbicide’s effectiveness. In
alkaline soils, above pH 7.5, reestablishment
of competitive vegetation may be difficult due to residual herbicidal action on
germinating seedlings.
Caution: Only apply to noncrop sites. Chlorsulfuron is a selective broadleaf
herbicide that also affects many grasses. Follow
the label directions, especially as they apply to herbicide persistence in the
soil and effect on any competitive
vegetation. Do not contaminate water.
Imazapic (Plateau®)
Rate: Use 8 to 12 ounces of Plateau® per acre or 2 to 3 ounces a.i. per acre.
Time: For best results, always use a methylated seed oil at 2 pints per acre.
Apply in the fall after a late frost (late October
through November). As long as there is some green and/or leaf tissue remaining,
good control can be achieved.
This timing usually corresponds with fall basal growth. Applications made prior
to this will result in poor control.
Remarks: Plateau® may not control some naturally occurring weed biotypes (plants
within a species with a slightly different
genetic makeup) with resistance to this and/or other herbicides with an ALS/AHAS
enzyme inhibiting mode of
action. When treating ALS/AHAS resistant biotypes, tank mix Plateau® with an
appropriately registered herbicide
having a different mode of action and sequentially treat the area to ensure
control.
Caution: No grazing restrictions exist, but do not harvest hay for at least 7
days following application of Plateau®. When
cool-season grasses such as bluegrass and smooth brome are present, do not
exceed 8 fluid ounces per acre.
Glyphosate (Roundup®, Aquamaster™, Rodeo®, or Aquamaster™)
Rate: Use 1 1/2 pints to 2 quarts according to label rates plus 2 quarts of
nonionic surfactant per acre.
Time: Apply when plants are actively growing before flower bud formation.
Repeated applications will be necessary; a
single application is marginally effective.
Remarks: Glyphosate is a nonselective herbicide that kills most plants,
including those that compete with new weed seedlings.
Wait 10 days after treatment, then seed with locally adapted species.
Caution: Follow the label recommendations and precautions, especially for use in
and near water.
Imazapyr (Habitat® or Arsenal®)
Rate: Use 1 1/2 pints to 2 quarts per acre.
Time: Apply to nearby establishing plants or at bud stage. A fall application
may be effective too.
Remarks: Remove stubble before making an application. If plants are tall, mow
them, remove the mowed material and
allow the plant to resprout before making the application.
Caution: Registered for use around water. It is not necessary to wet the foliage
until the herbicide runs off. Do not allow the
herbicides to drift.
If you arrived at this page from another link and would like to know more about the Spring Creek Region Cooperative Weed Management Area please click here: SCR CWMA