Whitetop is native to Russia and Eurasia and was accidentally introduced into the United States in contaminated crop seed in the early 1900s. Whitetop was first discovered in Gallatin County, Montana in 1916.
It typically inhabits open, sunny areas that have been recently disturbed. These areas include over-grazed pastures, waste areas, roadsides, and open grasslands.
Whitetop is a creeping perennial and can grow up to 2’ in height with rhizomatous roots, which can extend 2’ down and up to 12’ out.
The plant is silvery gray-green in color and its leaves are lance to arrowhead shaped and covered with fine hairs. It produces numerous white flowers that have 4 petals on 1/2″ long stalks. These dense flowers create a white, flat topped appearance. One plant is capable of producing 1,200 to 4,800 seeds. Seeds are produced in fruiting pods that contain 2 chambers, each capable of producing one seed.
Seeds are oval in shape and reddish brown in color. Seeds can remain viable in the soil for up to 4 years! Seeds can germinate in the fall or in the spring.
Whitetop is difficult to control because it can reproduce through rhizomes as well as seeds. It often requires many years of repetitive herbicide treatments; integrated weed management techniques such as hand pulling and herbicides when combined work best in controlling whitetop.
Article source: Montana Noxious Weed Education (www.agr.mt.gov)
Photo source: http://malag.aes.oregonstate.edu/wildflowers/images/Cardaria%20spp.BullyCreekWatershed.jpg