Control mustards in spring

By Casey Cisneros
Open Lands Weed Specialist

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One of the most powerful indicators that spring has returned to Colorado is the scent of the early bloomers.

The first flowers of the year are often the most aromatic, and in a lot of cases members of the mustard family. Some are native to Colorado, while others are considered noxious and difficult to control.

Plants in the mustard family (also known as brassicaceae or cruciferae family) are among the easiest to identify. When in bloom these flowers all have four petals. The petals are opposite each other and form a cross.

In northern Colorado many of the invasive mustards are winter annuals, meaning they germinate in late fall or winter and begin growing early in the spring. The annuals live one growing season, in which time they flower and set seed.

Some common winter annual mustards include flixweed, tumble mustard and blue mustard. Flixweed and tumble mustards grow to 3 feet in height and then break off at the base after flowering, creating a "tumbleweed." Blue mustards have purple flowers and a very pungent scent.

Other species of mustards have perennial life cycles, meaning they live longer than two growing seasons. Hoary cress and perennial pepperweed are perennials that can propagate through seed and creeping roots. Above ground, hoary cress grows up to 18 inches and has white flowers. The leaves clasp the stem and are often covered by fine white hairs. Perennial pepperweed grows 3 to 4 feet tall, has white flowers that are smaller than those of hoary cress and has leaves that do not clasp the stem.

Less predominant are biennial mustards. These plants live two growing seasons. The first is spent as a rosette and the second season the plant flowers and sets seed. Dame's rocket, a plant with a very showy flower, is a biennial mustard that was once sold in wildflower seed mixes. Dame's rocket is now on the prohibited sales list for nurseries in Colorado, due to the invasive tendencies of the plant. The lavender flowers of dame's rocket are very prevalent along the Poudre Canyon in the summer.

Learning to identify these plants before the flowering stage is difficult but important when trying to eliminate them. It is most effective to manage mustards early in the spring before the flowering stage. Many landowners make the mistake of waiting too long.

Mustards can be effectively controlled in pastures with various herbicides. The Larimer County Weed District recommends using Escort, Telar or Plateau tank-mixed with a non-ionic surfactant. Read the label for the suggested use rates. For perennial mustards, no other management technique will be sufficient besides the use of herbicides.

Mechanical removal, such as mowing and hand pulling, can also be an effective way of removing annual and biennial mustards. It is important to remove or mow these weeds prior to the flowering stage. When using a mechanical approach, an infested site may need to be revisited for several consecutive years until the seed bank in the soil is depleted.

In pasture and rangeland settings, mustards do not have any grazing value for livestock. The use of grazing to control invasive mustards is limited. Mustards will be the first weed issue of the season. Keep them in mind as the flags of spring are waved, and with early resolve that any mustard problem can be controlled.

Casey Cisneros works for the Larimer County Department of Natural Resources.