Source: Idaho's Noxious Weeds by Robert H. Callihan & Timothy W. Miller
BACKGROUND
Hoary cress (Cardaria draba) also known as whitetop) was introduced to the U.S. from Europe late in the 19th century. It was first noted around seaports on the east and west coasts, indicating seed may have been in the soil that was used as ballast for sailing ships. Hoary cress spreads both by seed and creeping roots, living in a wide variety of environmental conditions.
DESCRIPTION
Hoary cress is a perennialPlant that lives for more than 2 growing seasons that grows up to 3 feet tall. Leaves are grayish-green, clasping, lightly pubescentThe hairs on a leaf, stem, or flower, up to 4 inches long, and are shaped like arrowheads. Flowers are white with 4 petals, ΒΌ inch across, and borne in April and May; these dense flower clusters give the weed a flat-topped appearance early in the season, but this is lost as the stem elongates. Two small, flat, reddish-brown seeds are contained in each of the heart-shaped seed pods.
DISTRIBUTION
Hoary cress is found throughout the U.S., except from southernmost California across to southernmost Mississippi, and is extensive in Idaho.
CONTROL
Some herbicides are registered for hoary cress. there are no biological control agents for this weed.