Why is it a noxious weed?

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.

How would I identify it?

Leaves:

• alternate
• prickly edges, pointed lobes
• vary in size

Flowers:

• bright yellow
• 1 1/2 inches wide
• flowers open  2- 3 hours after sunrise and close around noon       
• bracts beneath flowers are green, bristly, have sticky hairs

Stems:

• 1 1/2 feet to 6 feet tall
• branch only at the top of the plant

Line drawings are taken from 1,000 Weeds of North America, copyright of XID Service, Inc and used with permission. Permission granted by the author.

How does it reproduce?

Perennial sowthistle reproduces by seeds and creeping roots.

Where does it grow?

Perennial sowthisthistle is found in a variety of places; cultivated fields (both grain and row crops), waste areas, meadows, sloughs, woods, lawns, roadsides, beaches, ditches and river and lake shores.     

What is the distribution in Washington State?

Click on map to enlarge.

• Perennial sowthistle has been documented in locations throughout Washington. Refer to map for distribution levels in specific counties.
• If you think you've seen this weed,  please contact your county weed coordinator or us at noxiousweeds@agr.wa.gov.

• Distribution map based on 2003 data.

How do I control it?

Cultural: Information not available at this time.

Herbicide: Please refer to the PNW Weed Management Handbook, or contact your county noxious weed coordinator.

Mechanical: Depending on the timing and type, tillage can reduce perennial sowthistle stands. Some existing evidence suggests that mowing would not be as effective as tillage as a control method.

Biological: Since perennial sowthistle is palatable to both sheep and cattle, pasturing infested land can be an effective control method There are several insects that have shown to control perennial sowthistle, however none are available in Washington.

Are there plants that may be confused with Perennial sowthistle?

For more information