Whitetop (Mustard Family), a native of Eurasia, was introduced to North America in contaminated seed. Whitetop is a relatively long-lived, rhizomatous perennial forb. It has numerous white flowers with 4 petals, giving the plant a white, flat-topped appearance. Leaves are lance-shaped, alternate on the stem, and covered with soft white hairs. Mature plants can reach 2 feet tall. The roots usually occur to a depth of 30 inches, but some can reach 12 to 30 feet. The deep roots and rhizomatous nature of this plant make it difficult to control.

Habitat

Whitetop prefers open, unshaded areas. It occurs on fields, waste areas, meadows, pastures, croplands, and along roadsides. It grows well on alkaline soils that are wet in late spring. Whitetop generally grows better in moist sites or areas with at least 12 inches of annual precipitation.
Whitetop invasion of arid rangelands is not common.
This weed spreads vegetatively and can eliminate native vegetation. In the absence of competition, a single plant can produce more than 450 shoots and spread over an area 12 feet in diameter in a single year. With competition,
a plant does not usually exceed 50 shoots per year.

Biology and spread

Whitetop reproduces by vegetative shoots and seeds. Plants emerge in early spring and flower in early summer. The plants usually set seed by mid-summer. If conditions are favorable, a second crop of seeds can be produced in the fall. A typical plant can produce 1,200 to 4,800 seeds each year. Buried seeds usually remain viable for about 3 years. Seeds are dispersed along roads, railways, and waterways. Seeds can be transported by water, wildlife, livestock, vehicles and Photo by Cris Evans equipment. Seeds are also dispersed to new sites in mud on boots and impure materials like mulch, forage and feed grains, crop and grass seed, top soil, and gravel.

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