Whitetop (Hoary Cress)
- Difficult to control due to an extensive and deep root system
- Resistance to many chemicals
- Capable of tainting meat and milk of grazing animals
- Capable of poisoning livestock
- Quickly establishes in disturbed areas
A stout, erect perennial in the mustard family.
- Stems are upright, grayish, and can grow to 2 feet tall.
- Leaves are blue-green to gray green that are alternate, covered with soft white hairs, and lance to arrowhead shaped. Upper leaves clasp stem.
- Flowers are numerous, white with four petals borne on ½ inch long stalk. Dense clusters create a white flat-top appearance.
- Seed/Fruit are heart shaped capsules with reddish brown seeds.
It prefers soils with neutral to alkaline pH and disturbed sites, including excessively grazed areas. It can be found in a variety of non-shaded habitats such as fields, meadows, pastures, open grasslands, waste areas, roadsides, watercourses, along irrigation ditches, and at the edge of riparian habitats.
The plants can spread rapidly. A single plant can eventually form a large colony, producing a dense monoculture that can crowd out native species. In the absence of a competitor, a single plant can spread over an area 12 feet in diameter in one year. Types of disturbance which promote colonization and spread include grazing, irrigation, and cultivation. The species also contains compounds of glucosinolates, which can be toxic to some animals.
- Mechanical: pulling and grubbing should be done within 10 days of plant emergence and before flowering and seed set; till and repeat tilling to remove root systems; clean all equipment before moving from the infested site; flooding can be used because seeds lose viability after being in wet soil for one month; mowing can help control infestation by reducing seed production in existing plants but will not eradicate existing populations.
- Chemical: Successful control usually requires repeated applications with foliar herbicides. It can be effectively controlled using any of several readily available general use herbicides. Metsulfuron can be used on rosettes but it is ineffective after the plants start to bloom. 2,4-D is effective on mature plants. Chemicals provide the most control when applied at the rosette state or flowering stage when carbohydrates are moving from above to below ground and herbicides are more likely to be transported to the roots. Follow label and state requirements.
- Biological: None to date in the United States.