Hoary cress, whiteweed, peppergrass, heart-podded hoary cress, hoary cardari
Whitetop is a perennial weed that is in the mustard family and can grow up to 2 feet in height. The roots are extensive and deeply penetrating, both laterally and vertically and small buds and the roots create new shoots. The leaves are grayish-green in color and the upper leaves clasp the stem and can be up to 4 inches long and the leaves are shaped like arrowheads. The leaves are covered in fine hairs making them soft. Leaves at the base of the plant form a rosette early in the spring and are larger than the leaves on the stems. Flowers are white with 4 petals and about ¼ inch across and shaped like a cross. They bloom from the middle of May to June. Flowers form clumps at the ends of the stems and give the plant a flat-topped appearance and the flowers are cream in color and cast as they mature. Seed capsules are flat and heart shaped with 2 reddish, brown seeds encased in pods and will produce around 3,000 seeds annually. This plant will reproduce by seed or by the roots.
Field Pennycress and common yarrow are commonly misidentified as whitetop. Pennycress has darker green leaves with serrated edges, and is an annual plant. Yarrow has fern-like leaves and emerges later in the summer than whitetop.
When looking for whitetop one will look for a flower cluster that is flat-topped and white to cream in color. The leaves and stems have a grayish-green color and the leaves are soft and covered in fine hairs.
Whitetop prefers open, unshaded areas and can be found on a wide variety of soil types. It generally grows better in moist sites or areas of moderate rainfall. Whitetop has an attraction to moisture as it has been found in sub irrigated pastures, ditch banks, irrigated cropland and the edges of riparian areas or can be found in disturbed sites, including over grazed areas, waste areas, roadsides and open grasslands.
There are herbicides and other control methods that commonly control whitetop. Herbicides must be applied early in the spring before plants mature and set seed - this often occurs before June. Escort and Telar have shown to provide the most effective control. Chapparal (milestone+escort), 2,4-D and Dicamba have some level of control. Tordon is not effective on whitetop. For more information on these herbicides and other control methods contact the Weed and Pest office.
In the Pacific Northwest with the abundant rainfall the roots have been shown to grow in the soil up to 30 feet in depth. Seeds may have been in the soil that was used for the ballasts of sailing ships because it was first discovered around seaports on the coasts in the U.S.