Controlling invasive Whitetop requires integrated methods
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Unless you haven’t been paying attention at all to flowering weeds, you have noticed the white blossoms covering pastures, rangeland, ditch banks, disturbed areas and even cropland this spring in Lake County. However attractive the blossoms are, the plant producing them is a dangerous invader to desirable plant communities. Commonly known as whitetop, this member of the mustard family originated in the former USSR, northern Iran, Afghanistan and Pakistan, arriving in the U.S. during the late 1800’s as early as 1916 and is now estimated to infest 32,000 acres in Montana and 8,000 acres in Lake County alone.
Dense blooming stands look very much like a late melting patch of snow. Individual white flowers have four petals borne on slender stalks about a half-inch long. Plants normally grow from 10-24 inches tall. Leaves are grayish green, arrowhead shaped, with smooth and occasionally finely toothed edges, ranging from three quarters to three inches in length, clasping the stem alternately.
Whitetop reproduces by seeds that can be spread by wind, along waterways, irrigation systems, on vehicles, machinery and in hay. However, what causes the rapid expanse is primarily the precocious root system that spreads via rhizomes, underground stems capable of producing shoots that emerge as plants. A single plant can spread to an area 12 feet in diameter in its first year.
Rapid root growth reaches 12 to 30 feet and in some cases, whitetop can place its roots directly into the water table. Because of the deep root system and ability to reproduce vegetatively, these weeds are very difficult to control.
Successful management of whitetop requires integrating a variety of methods to keep the infestation to tolerable levels. As with any weed control program, the most cost effective method is to prevent invasion. Eliminate or at least restrict seed dispersal. Refrain from driving vehicles and machinery through infested areas. Livestock grazing management is essential to maintain competitive grass plants to slow or prevent weed encroachment and never purchase or feed hay known or suspected to contain whitetop seeds.
Hand pulling of above ground plant parts is ineffective. Successful hand pulling or digging requires complete plant removal within 10 days after weed emergence throughout the growing season for two to four years. Moving to ground level during flowering reduces seed production but does not provide long-term control. However, mowing integrated with herbicide use can be effective. Whitetop can be controlled using herbicides, although it is difficult because an aggressive reapplication program is necessary. Herbicides that have proven to be effective are Chaparral, Forefront, Metcel, Telar, and to a lesser degree 2,4-D. No single treatment provides long-term control. A key component of any integrated management program is sustained effort and constant evaluation. For more information on whitetop and its control, contact the Lake County Weed Control Office or the MSU Lake County Extension Service.
