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Pacific Northwest Research Station
Blue Mountains National Resources Institute

Forestry and Range Sciences Laboratory
1401 Gekeler Lane
La Grande, OR 97850

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BMNRI Home > Publications > Weeds > Whitetop

Publications: Noxious Weeds

Explosion in Slow Motion: A talk by Jerry Asher about noxious weeds in the Blue Mountains

Click on a weed to learn about how to find it and kill it!

Common Crupina
Diffuse Knapweed
Russian Knapweed
Spotted Knapweed
Purple Loosestrife
Perennial Pepperweed
Tansy Ragwort
Medusahead Rye
Rush Skeletonweed
Yellow Starthistle
Canada Thistle
Musk Thistle
Scotch Thistle
Dalmatian Toadflax
Mediterranean Sage
St. Johnswort
Leafy Spurge
Dyers Woad

Wanted: DEAD!


Alias: Hoary cress, pepperwort

Stems: Up to 3 feet high.

  • Leaves: Grayish-green, up to 4 inches long, shaped like arrowheads. Nearly entire to finely toothed and bearing soft fine hairs. Lower leaves stalked, upper reduced and sessile.
  • Flowers: Numerous and small, four sepals and petals, petals about 1/4-inch long and white. Flowering period is in early May.
  • Fruits: Inflated, 1/8-inch long, heart-shaped at base and topped by a persistent style. Prominently veined at maturity, bearing two (or four) reddish-brown, small, flat seeds.

Whitetop can establish itself in a variety of soil types and environmental conditions: dry pastures, hay meadows and roadsides, cultivated crops. A single plant can send out 400 shoots in a year. Roots develop to depth of several feet, making control difficult. It spreads by seed and root.

Control: Integrated pest management is the best method of controlling this weed.

  • Biological: Dense stands of perennial grasses will out-compete whitetop. Pasture grasses will slow spread if not overgrazed. Growing small grains in infested fields will suppress whitetop once a canopy is formed. No insects or parasites are available in the United States (as of Nov. 1991).
  • Chemical: Most easily controlled with foliar herbicides applied during rosette stage. Depends on where infestation is located, what kind of herbicide and application is allowed.
  • Mechanical: Cultivating fallow ground no more than 10 days after weed emergence will eventually eliminate the weed. Close mowing will also reduce seed production but will not eliminate.

Report all sightings to your local Weed Board

US Forest Service - Pacific Northwest Research Station, Blue Mountains National Resources Institute
Last Modified: Monday, 16 December 2013 at 14:18:43 CST

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