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Whitetop

Scientific Name:Cardaria draba

Family: Brassicaceae (Mustard Family)

Other common names: hoary cress

Life-Cycle: Perennial that reproduces by seed and rhizomatous roots




Whitetop Quick Guide

Description
Bloom
(varies by elevation)

What to Do

When?
Invades Undisturbed Land
State Class
8-20" tall on an upright stalk with dense clusters of flowers. Leaves somewhat hairy, large and lance-shaped. Can cover large areas.
Clusters of small white flowers bloom in May & June. Flowers have 4 petals in a cross shape.
Aggressively treat new populations. Repeatedly handpull small populations; consider herbicides and competing vegetation.
April-May when ground is wet, before it goes to seed.
Yes! Colonizes a variety of habitats but tends to prefer moist soil. Rapidly expanding in the Methow.

C
whitetop rosette
mature whitetop plant
top of the flower

General Description
. Whitetop is a perennial that prefers moist, disturbed places such as sub-irrigated pastures, hay and alfalfa fields, rangeland, roadsides and ditch banks.
. It spreads via its creeping deep root system, and seeds; it is spreading rapidly in the Methow and is hard to eradicate.
. From a distance, whitetop can be confused with white flowered native plants like yarrow and desert buckwheat. A close up look reveals a hardy herbaceous plant that forms dense monocultures if not controlled.
. An upright single stem eight to twenty inches tall quickly forms clumps of many stems.
. A flat or dome-shaped cluster of tiny white flowers tops each stem; each flower has four petals. Flowers become cream-colored with age.
. At first, leaves form a rosette at the base of the stem and are somewhat grayish green, hairy and lance-shaped. As the plant grows, leaves become more bright green, waxy and broad.

Life-Cycle
. Whitetop is a perennial, meaning it comes back year after year from the same root system, which in this case is continually expanding downward and outward.
. Blooms in late April, May and early June; begins producing seeds about a month later.
. If conditions are right, a second bloom may happen in late summer/early fall.
. Spreads via seeds (look like heart-shaped capsules) and extensive roots.
. Roots regenerate after disturbances, including hand-pulling if you don't get the entire root.

Prevention & Control

    Prevent
    . Detect and eradicate new plants early; survey your property at least a few times each spring/summer.
    . Refrain from driving vehicles and machinery through infested areas during seeding.
    . Livestock should not graze weed-infested areas during flowering and seed set.
    . Avoid whitetop patches during excavation, cultivation or other ground disturbance.
    . Screen irrigation water before it enters a field or your irrigation pipes.

    Hand-Pull
    Hand-pulling or digging should only be an option on very small populations, as early in the season as possible (within 10 days of emergence is recommended). You must get the entire root to be successful, and repeat often to get new plants that continue to emerge.

    Mowing, Grazing, Cultivation & Biocontrols
    . Mowing or weed-whacking at ground level during flowering reduces seed production but does not provide long-term control.
    . Planting competitive legumes, such as alfalfa, can reduce whitetop. Cultivation needs to be deep (at least 6") and repeated to expose and kill roots before planting a crop.
    . Neither grazing nor burning is recommended for controlling whitetop.
    . Biocontrol research is being done but no biocontrol for whitetop exists now.


    Herbicides
    .Spraying an herbicide while plants are in the rosette stage, both early in the spring as well as later in the fall can be very effective; repeated applications may be needed for 2-3 years.
    . Because the leaves are waxy, a surfactant needs to be mixed with the herbicide.
    . Use a "selective" herbicide if you don't want to kill native grasses when you spray.

    See the Herbicide section of the "Toolbox of Weed Control Methods" for more details on spraying.

Interesting Tidbits
. A single plant, starting on a small stalk, can spread to an area 12 feet in diameter in its first year. Subsequent increases range from 2 to 5 feet per year.
. Typically just after arrowleaf balsamroot have covered hillsides in yellow and are starting to fade, you will begin to see large areas covered in white - this is whitetop.
. Whitetop is in the mustard family and has the characteristic spicy mustard flavor of arugula or cress; young leaves and blooms are surprisingly tasty additions to salads, just be sure it has not been sprayed with herbicide.

Resources & Photos
* Washington State Noxious Weed Control Board Hoary Cress/Whitetop Page

* Detailed Factsheet from Lincoln County, WA

* Okanogan County Noxious Weed Control Board

* More Images:http://biology.burke.washington.edu/herbarium/imagecollection/taxon.php?ID=932

* More Images: http://www.invasive.org/weedcd/species/5232.htm

 
 
 
 
 
 
315 Riverside Avenue / PO Box 71    Winthrop, WA 98862     509.996.2870