Weed Control

Park City Municipal is working hard to eradicate noxious weeds in the Park City.  There are two noxious weeds that are widespread in Park City and Summit County, particularly on the east side. Dyer's Woad and hoary cress are easily recognizable by the monocultures they form in many recently disturbed areas or along roadsides. Large patches of white flowers or yellow flowers are likely one of these two weeds. Dyer's Woad can be effectively controlled by pulling and putting them in trash bags (especially if it has gone to seed), whereas it is not recommended to pull hoary cress, as the extensive root system will sprout new plants.

Dyer's Woad (Isatis tinctoria) is a plant belonging to the mustard family. In Europe, this plant has been cultivated as a source of blue dye and for medicinal properties since the 13th century. In the early 1900's, it was introduced into the West as a contaminant in alfalfa seed. To identify this weed, the leaves are simple, have petioles, are bluish-green with a prominent whitish vein on the upper surface of the blade. The flower has a flat top with yellow petals. The fruit is a purplish-brown to black pod containing one seed.

This noxious weed is found mostly in disturbed sites, such as range, cropland, dry areas, woodlands, and pasture sites. Dyer's Woad is problematic because it overtakes native grass, and most livestock and wildlife don't graze it. However, Dyer's Woad doesn't need disturbance to invade a site. Dyer's Woad is spread from place to place by seed. Each plant produces an average of 350-500 seeds per plant, with some plants producing well over 10,000 seeds in one year!

Control/Management
Multiple tools can and should be used in the control of dyer's woad. One of the simplest and most effective control methods is hand-pulling. In parts of Utah, this method has been used by high school students and other volunteers. This is most effective with small populations and should be done 2-3 times a year for several years to be effective. A biocontrol has shown limited success in controlling this weed.

White top or Hoary Cress (Cardaria draba) also belongs to the mustard family and is native to western Mediterranean countries and the Middle East (Turkey, Israel, Syria, Iraq and Iran). Hoary cress likely entered North America in contaminated alfalfa seed. The leaves are blue-green in color and only the lower leaves are stalked; the upper leaves are stalkless and clasp the stem with 2 earlike lobes. The short, flowering branches bear many very small flowers, each with 4 petals, giving the plant a flattop appearance. As seen in some parts of Summit County, hoary cress can form dense monocultures that displaces native plants, degrades wildlife habitat, decreases land value and species diversity. This plant grows in open, unshaded areas where sub-irrigated pastures, croplands, rangelands, ditch banks, roadsides, and waste areas exist.
Hoary cress reproduces by both seed and root fragments. Each flowering stem can produce 850 seeds annually. Seeds are spread by wind, waterways, and vehicles. Buried seeds can remain viable for up to 3 years. In addition to spreading by seed, a single white top plant can send out rhizomes that will spread out over 12 feet in the first year. These rhizomes send up shoots that act as a new plant.         

Control /Management
This is a very difficult weed to control. Control requires an integrated plan with constant monitoring and work. Sites must be rechecked throughout the growing season, for 4 years. No biocontrol is currently available.