By Eric Jones
Many fields that are planted to winter wheat, no-till, or have yet to be tilled may have a healthy infestation of field pennycress or shepherd’s purse. The heavy infestation of these weeds is likely caused by a mild winter with early moisture to promote germination and growth.
Identification
These two species can be easily confused with each other. Field pennycress has long, rounded leaves with rounded, toothed margins (Figure 1), while shepherd’s purse has oblong leaves with deeply lobed margins (Figure 2). These species germinate primarily in the fall or early spring. The early stages of growth are in a rosette, but as the plant matures, elongation or “bolting” of the stem occurs. Seed heads are an easy way to identify the two species. Field pennycress has a round, notched seedhead (Figure 3), while shepherd’s purse has a heart-shaped seedhead (Figure 4). However, identification should occur before the plants develop seed heads, as viable seeds could be produced, and many management tactics are not effective at this stage.
Management
Management implementation should occur before bolting occurs. If management tactics are delayed to the bolting stage, control can be decreased, and often plants have produced viable seed that will be added to the soil. Both species are susceptible to tillage when small. Herbicides are more effective when applied to the plants in the rosette stage. Glyphosate (Roundup) is effective when applied as a preplant burndown. 2,4-D can be tank-mixed with glyphosate to increase effectiveness and spectrum of weed control when applied as a preplant burndown. 2,4-D and bromoxynil (Brox, Maestro, Moxy) are effective when the species are present in a wheat crop. Tribenuron (Express, Taquet, Victory) and metsulfuron (Ally, Patriot, MSM) are also effective herbicides that can be applied in wheat.
Usually, the two species are rarely at heavy enough densities to cause a yield loss. The important reason to control these two species is that both can potentially be a secondary host for soybean cyst nematode. The importance is further demonstrated by the fact that the soil samples submitted for soybean cyst nematodes egg screening to the South Dakota State University Plant Diagnostic Clinic in 2023 averaged 10,000 eggs per sample. If the infested field is to be planted into soybean, diligence should be taken to effectively manage these two species (and other weeds) before planting. Managing these species in other crops should be a priority as well, so no plants are present to host the soybean cyst nematode for soybean planted in later years.
Source : sdstate.edu