Field pennycress (Thlaspi arvense), a member of the mustard family, is a widely encountered plant across various landscapes, from agricultural fields and gardens to roadsides and disturbed areas. Also known as fanweed or stinkweed, it is often considered a nuisance in cultivated spaces. Identifying field pennycress early in its seedling stage is important for effective management, allowing for timely intervention before the plant establishes itself.
Identifying Field Pennycress Seedlings
Cotyledons
The first leaves to emerge from a field pennycress seedling are its cotyledons, which are typically oval-shaped. These initial leaves are often described as bluish-green in color and are generally hairless. They can vary slightly in size, measuring approximately 0.2 to 0.4 inches long by 0.1 to 0.3 inches wide. A distinctive feature of these cotyledons is their noticeable petioles, or leaf stalks, which can be up to 0.25 inches long, and they may have tips that curve slightly downwards.
First True Leaves
Following the cotyledons, the first true leaves of field pennycress emerge, initially appearing opposite each other. These leaves are typically oval to spatulate in shape, with margins that can be wavy or slightly toothed. As more true leaves develop, they transition to an alternate arrangement on the stem. Young field pennycress leaves are generally smooth, without hairs, and often display a distinct whitish midvein. Crushing the foliage of field pennycress, even at the seedling stage, can release a characteristic unpleasant, often described as garlic-like or turnip-like, odor, which serves as a reliable identification cue.
Stem and Growth Habit
In its early seedling phase, field pennycress develops a short stem that supports the emerging leaves. The plant’s initial growth habit involves the formation of a basal rosette, where young leaves are arranged in a circular cluster close to the ground. This rosette can spread up to 6 inches in diameter as the seedling grows. The leaves within this rosette are often light green and may exhibit a waxy appearance. This low-growing rosette allows the plant to efficiently capture light and nutrients before it eventually sends up an erect flowering stem.
Life Cycle and Common Habitats
Field pennycress is classified as an annual or winter annual plant, completing its life cycle within a single year, though this often spans two calendar years. Seeds can germinate in the fall, forming a rosette that overwinters and resumes growth in early spring. Spring-emerging seedlings are also common, with a peak in emergence occurring early in the season.
The plant thrives in disturbed soils and is a frequent inhabitant of cultivated agricultural fields, including those used for horticulture and nurseries. It is also commonly found in gardens, along roadsides, and in waste areas. Field pennycress generally prefers full sun and moderate moisture conditions, often growing well in loam and clay soils.
Managing Field Pennycress
For small infestations, manual removal methods like hand-pulling or hoeing are effective. Remove the plants before they produce seeds, as each plant can generate thousands of seeds that remain viable in the soil for several years. Severing the plants just below ground level on a warm, dry day helps ensure they dehydrate and do not regrow.
Cultural practices can also help discourage field pennycress growth. Delaying the planting of spring or fall crops can allow more pennycress seeds to germinate, which can then be addressed through tillage before crop planting. Utilizing dense winter cover crops, such as rye or spelt, can suppress field pennycress by competing for resources.