Identification and Management for Shepherd’s Purse and Field Pennycress

April 15, 2025

Shepherd’s purse and field pennycress are becoming more prominent and problematic for crop production. Factors that may contribute to the prevalence of these weeds in corn and soybean fields include the increased adoption of no-till, a decrease in the use of residual herbicides, and milder winters with more open fall and springs.¹ Awareness and understanding how to identify these weeds and use proper control timing can help combat this issue.

Classification

Understanding the lifecycle and habitat of a troublesome weed is a key factor for successful control. Both Shepherd’s purse and field pennycress belong to the mustard family. They are both cool season winter annuals. A winter annual completes its lifecycle within one year, but over the course of two calendar years. Confusing right? During the fall of year one, these winter annuals germinate, grow and over winter as a rosette. Then in early spring of year two, they resume their growth, flower and set seed. This allows them to be green and ready to grow as soon as the snow melts. Their circular rosette growth habit makes them excellent competitors for seedling water, nutrients, light, and space.

In many states, Shepherd’s purse and field pennycress are classified as invasive species, originating from Europe. They are classified as noxious weeds in some states and as required by state law, they must be controlled and eliminated.

Control and Management

Because of their winter annual life cycle, there are two times for potential control; late fall and early spring. Both times can include mechanical or chemical control methods.

The type of control and management is primarily dependent on the tillage system. If some form of tillage is allowed, mechanical removal post-harvest or pre-plant is a good way to eliminate the rosette and prevent early spring competition. Greatest control has shown to occur when herbicides are applied in the fall, prior to frost. Like perennials, winter annuals bring photosynthetic energy, and the herbicide, down into the root growing points.

Identification

Identification between Shepherd’s purse (Figure 1) and field pennycress (Figure 2) as a seedling and rosette can be tricky. Understanding leaf shape and a good set of eyes to see small hairs is most helpful. If the rosette has bolted, sending an erect flower stalk from center of the plant, identification is simple. The seedpods are distinctively different with Shepherd’s purse being heart shaped (Figures 3 and 4) and field pennycress being round (Figures 5 and 6). Table 1 outlines key characteristics for both weeds.

Table 1. Identification Characteristics of Shepherd’s Purse and Field Pennycress.

Figure 1. Shepherd’s purse rosette. Image courtesy of Steve Dewey, Utah State University, Bugwood.org.

Figure 2. Field Pennycress rosette. Image courtesy of Steve Dewey, Utah State University, Bugwood.org.

Figure 3. Shepherd's purse seedhead.

Figure 4. Shepherd's purse seed. Image courtesy of Bruce Ackley, The Ohio State University, Bugwood.org.

Figure 5. Field pennycress immature seed head. Image courtesy of Steve Dewey, Utah State University, Bugwood.org.

Figure 6. Field pennycress mature seed head. Image courtesy of Ohio State Weed Lab, The Ohio State University, Bugwood.org.

Lindsey Novak
Channel Agronomist

Source

¹Sandell, L., Bernards, M., and Knezevic, S. 2009. Uncontrolled winter annuals rob your crop of soil nutrients and soil moisture. CROPWATCH. University of Nebraska-Lincoln. https://cropwatch.unl.edu/uncontrolled-winter-annuals-rob-your-crop-soil-nutrients-and-soil-moisture/

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