WSU Extension


Weeds : Field pennycress (Fanweed) : Thlaspi arvense
(revision date: 3/14/2019)

Family: Brassicaceae (Cruciferae)
Cycle: Annual
Plant Type: Broadleaf

Use Integrated Pest Management (IPM) for successful weed management.

Field pennycress grows six to eighteen inches tall, branching mainly in the upper, flowering portion of the plant. The leaves are elongate, hairless, and alternate, with larger leaves at the base of the plant and smaller leaves above. The lower leaves have petioles, while the upper leaves lack petioles and may clasp the stem. Leaf shape is variable, with some leaves shallowly toothed and others with smooth margins. Flowers are borne on the tips of branches at the top of the plant. The small blossoms have four white (sometimes pinkish) petals. Flowers occur singly on short stalks. Seeds are borne in a roughly circular pod about 2/5 inch in diameter. The pod has a thickened central portion surrounding the seeds and a thin, fan-like wing surrounding this central part. Mature pods split in half along a center partition. The tiny seeds are dark reddish-brown at maturity. This plant has a strong odor, sometimes described as onion-like.
Field pennycress is found in fields, waste places, along roadsides, and in disturbed areas.

Management Options

Non-Chemical Management
  • Reduce weed establishment by maintaining a healthy planting or turf area to provide competition.
  • Cultivation (rototilling or hoeing) will effectively eliminate plants.
  • Hand-pull to eliminate weeds.
  • Mowing to prevent seed production is a very effective means of management. In lawns, mowing regularly at the proper height for the grass species may help minimize weed growth and invasion.
  • Careful digging is useful to manage weed populations. However, digging can carry undesirable weed seed to the surface and foster further germination.
Select non-chemical management options as your first choice!

Chemical Management

Apply according to label directions. Glyphosate products should be applied as spot treatments only! There are also products available to licensed applicators for use to control this weed. NOTE: Some ingredients listed here are only available in combination. Read the label carefully on combination products to make sure the product is suitable for your specific situation.

Landscape areas
  • glyphosate
  • dichlobenil
  • products containing diquat
Turf areas
  • products containing 2,4-D
Bare ground areas
  • glyphosate
  • products containing diquat
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Caption: Field pennycress fruits
Photo by: D.G. Swan
Caption: Field pennycress leaves
Photo by: J.A. Kropf
Caption: Field pennycress flower heads
Photo by: R. Parker
Caption: Field pennycress seedling
Photo by: D.G. Swan