Perennial Sowthistle
Sonchus arvensis ssp. arvensis
Washington State Classification
Class C — Widespread, County-Selected Control
Perennial sowthistle is classified as a noxious weed in many states and provinces.
Quick Reference
Identification
Growth Habit
A deep-rooted perennial herb, perennial sowthistle has upright, hollow stems with bitter, milky juice.
Leaves
Leaves are alternate with prickly edges and pointed lobes and varying in size. Leaves become smaller and less lobed moving up the stem.
Flowers
Flowerheads are bright yellow and 1.5 inches wide. Flowers open 2 to 3 hours after sunrise and close around noon. Bracts at the base of flowerheads are green, bristly and have sticky hairs.
Fruit & Seeds
Seeds are small, around 0.1 inches long with ridges on each side.
Impact
Perennial sowthistle is classified as a noxious weed in many states and provinces. It is a problem in several crops where it causes economic losses due to reduced crop yields, increased cultivation and herbicide expenses and land depreciation. Perennial sowthistle was changed from a Class B to a Class C noxious weed in 2013.
Ecology & Spread
Habitat
Perennial sowthistle is found in a variety of places such as cultivated fields (both grain and row crops), waste areas, meadows, sloughs, woods, lawns, roadsides, beaches, ditches as well as river and lake shores. Please click here to see a county level distribution map of perennial sowthistle in Washington.
Spread Mechanisms
Reproduction
Perennial sowthistle reproduces by seeds and creeping roots.
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Control Methods
Mechanical
- Depending on the timing and type, tillage can reduce perennial sowthistle stands. Some existing evidence suggests that mowing is not as effective as tillage.
Biological Control
- Since perennial sowthistle is palatable to both sheep and cattle, pasturing infested land can be an effective control method. There are several insects that control perennial sowthistle; however, none are available in Washington.