Stevens County Noxious Weed Control
Board This web site will help
you identify & control noxious weeds. Conventional & biological control
(BioControl) information and photographs are here. Maps & related
information are included.
Hoary cress & Hairy whitetop are closely related
species of mustards. All identifying traits apply to both, unless stated
otherwise.
Key identifying traits
Flowers are small & white and form dense flat-topped clusters
from May to early June
Alternate, oblong to arrow-headed leaves clasp the stem; they range
from ¾-3" long, have a bluish-green color and a waxy feel to
them
Fruit is heart-shaped (hoary c.) or globe-shaped (hairy w.) and
tipped with a "beak"
Seeds are oval and reddish-brown and come two per pod (hoary c.) or
four per pod (hairy w.)
Biology and ecology
Long-lived perennials, reproducing by seed and underground
horizontal roots (rhizomes)
Introduced from central Europe & western Asia
Will form a large dense spreading colonies if not controlled
Thrive under a wide variety of soil conditions
Bloom and set seed early in the growing season
Problem in ditches, crops and pasture, once established it is very
difficult to eradicate
Control
Prevention –
Learn to
identify plants; know your property; target small infestations
aggressively
Biological – No known biological agents yet
Cultural – Good vegetative cover helps but does not prevent
establishment or spread
Mechanical – Cutting/tilling will not achieve control due to
the underground root system
Chemical – Several effective at label rates but may require
repeat treatments to kill root systems; best before bloom or in the fall;
refer to the
PNW Weed Management Handbook for specific chemical recommendations
rosettes
pods of hairy whitetop
pods of hoary cress
infestation
Where found –
Found
in scattered locations throughout Stevens County, especially in
abandoned crop land.
