There could be tiny ticking time bombs growing in your wheat fields right now. Looking small and innocent today, these weeds could bolt into much larger, more competitive weeds this spring if left uncontrolled, stealing yield and profit.

“Mustard plants such as field pennycress, bushy wallflower or treacle mustard, flixweed, tansy mustard, and blue mustard in wheat fields are often not noticed until the mustards bloom in the spring,” explains Sarah Lancaster, a weed management specialist at Kansas State University. “As a result, farmers often do not think about control until that time.

“Although it is possible to get some control with spring herbicide applications, mustard control is much more effective before they have flowered. Earlier applications are also more effective in preventing wheat yield loss due to mustard interference.”

Lancaster and Jeremie Kouame, weed scientist at the KSU Agricultural Research Center at Hays, suggest that scouting fields now, identifying if these weeds are present, and then developing a weed control strategy can prevent headaches and preserve yield.

For help on identifying key weeds in the mustard species common in wheat, see World of weeds: Mustard species, by Lancaster and Tyler Meyeres.

Here are tips from that resource to help distinguish between these weeds. Identification is important because controls can vary depending upon your key target weeds.

Related:Controlling mustard in wheat pays dividends

Blue mustard. Blue mustard seedlings have oval to oblong cotyledons; the first true leaves are alternate, and the leaves tend to have a rough surface. All green parts of the plant have white hairs, and the plant emits a unique, unpleasant odor. Once bolted, blue mustard is 12 to 18 inches tall. It eventually bears purple or blue flowers at the top of the plant.

Bushy wallflower. Also called treacle mustard, bushy wallflower emerges in the fall and overwinters as a rosette. Cotyledons are small and spoon-shaped, tapered at the base and slightly notched at the tip. The rosette has long, narrow leaves that are irregularly notched. Bushy wallflower grows 12 to 18 inches tall with bright yellow flowers.

Field pennycress. Pennycress emerges in the fall and overwinters as a seedling or rosette. It can emerge in the spring from seed. Cotyledons are oval to oblong and have a very long petiole, up to one-fourth inch. First true leaves are round to oval with a prominent midvein, without hairs. Leaves grow into a rosette and are oval with wavy edges and no hairs.

When field pennycress bolts, leaves are lanceolate in shape, attach directly to the stem, and have slightly toothed edges and pointed lobes. The plant ranges from 4 to 24 inches in height. Flowers are white and occur in clusters at the end of stems.

Pinnate tansy mustard and flixweed. These two weeds are very difficult to tell apart. Both emerge in the fall and overwinter as rosettes with finely lobed, lace-like leaves. Mature plants of both species are covered in dense, fine hairs. After bolting, leaves of both species are alternate on the stem. Flowers of both species are usually yellow and occur in small clusters.

Key differences when young: Pinnate tansy mustard has reddish-green to purple stems. Leaves are smaller, ranging from 0.25 to 2.5 inches long, while flixweed leaves range from 1.25 to 4 inches long. Pinnate tansy mustard flowers can also be yellow-green to white.

Key differences when mature: Flixweed sepals just below petals are longer than the petals. Pinnate tansy mustard siliques, or seed pods, are short and club-like with a prominent midrib. Flixweed siliques are longer and narrower, and attached at right angles.

Click through the slideshow to see photos of these weeds.