War on Weeds—weeds are everybody’s problem
Photo courtesy, Chris Evans, University of Illinois, Bugwood.org
THE ISSUE: Annual Sowthistle
Annual sowthistle (Sonchus oleraceus) is an annual weed found in agricultural fields and home gardens. Annual sowthistle is a well-known host for pests and diseases of crops, in addition, it utilizes valuable water resources, reducing yields for desirable crops. Annual sowthistle can produce up to 8,000 seeds per plant and seeds are dispersed easily by the wind.
Annual sowthistle is a member of the Asteraceae (sunflower) family. It can grow 1 to 4 feet tall and produces an elongated Hershey Kiss shaped yellow flower that opens like a dandelion. Its sessile leaves are deeply lobed with prickly margins. The leaves wrap around the stem and point straight back, as opposed to Prickly sowthistle whose leaves wrap around and down the stem. It has a hollow, spineless stem, and when broken open, exudes a white milky substance.
Integrated Pest Management (IPM) Options:
• Cultural – Annual sowthistle’s seeds do not remain viable when on the surface of the ground for more than a year but can remain viable if incorporated into the soil. Shallow tillage, of less than 3 inches will keep seeds from building up in the seed bank. In addition, annual sowthistle germinates well in wet soils, limiting the amount of standing water or saturated soils will reduce germination rates.
• Mechanical – Hand pulling annual sowthistle is easy because of its shallow root system. Shallow tilling or hoeing of annual sowthistle will pull up its roots. Remove the entire root, as re-rooting can occur.
• Biological – Grazing by sheep and cattle suppresses the growth of annual sowthistle making it more susceptible to other forms of control.
• Chemical – Preemergent and post emergent chemicals are both available for use with annual sowthistle. Post-emergency spot spraying has been found to provide excellent control. For more information on different chemicals to use refer to www.pnwhandbooks.org and search “Annual Sowthistle” in the search. Always read and follow herbicide label directions!
Tom Jacobsen, University of
Idaho Extension Educator in Fremont County. (208) 624-3102 [email protected] and Justin Hatch, University of Idaho Extension Educator in Caribou County. (208) 547-3205
