HPIPM:Annual sowthistle

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Asteranae
Order	Asterales
Family	Asteraceae
Subfamily	Cichorioideae
Tribe	Cichorieae
Genus	Sonchus

Scientific Name

Sonchus oleraceus

Common Name

annual sowthistle

Annual sowthistle (Sonchus oleraceus)

Compiled by Mark B. Major, Montana State Univeristy, Teton County Extension

and Marjolein Schat, Montana State University from the following sources:

http://plants.usda.gov/java/profile?symbol=SOOL

http://www.dowagro.com/ca/news/western/30-Mar-01.htm

http://www.ag.ndsu.nodak.edu/invasiveweeds/sonchus%20oleraceus.htm

Identification and Life Cycle

Annual sowthistle (Sonchus oleraceus) is an introduced annual in the aster family (Asteraceae). The stems are erect, 1-4 ft. high, hollow, and glabrous. The leaves are alternate with spiny and deeply lobed margins. Lower leaves are petiolate while the upper leaves are sessile. Leaf veins may be purple. Flower heads are numerous, yellow, and appear in corymbs. The seeds are flat achenes, approximately 0.12 inches long, ribbed lengthwise, brown, with a pappus of white hair at one end. Annual sowthistle is similar in appearance to perennial sowthistle and spiny sowthistle. Perennial sow-thistle has a long vertical rhizome-like root system whereas annual sow-thistle has a short taproot. Spiny Sowthistle has rounded lobes that clasp the stem whereas annual sowthistle has distinctly pointed lobes. Also, the leaf margins of spiny sowthistle are much more spiny or prickly than those of annual sowthistle.

Habitats

Annual sow-thistle thrives where moisture is available, especially on disturbed sites resulting from overgrazing, natural processes or cultivation. It is common in vacant lots, roadsides, and in cultivated fields and gardens.

Impacts

The overwintering rosette phase may serve as a reservoir for both plant viruses and their vectors. Annual sowthislte may also act as an alternate summer host to economically important aphids which are potential vectors of "yellow" virus disease. This weed may compete with other desirable plant species.

Biology and Ecology

Annual sowthistle reproduces only by seed. This weed germinates anytime between spring and fall when conditions are suitable. In general annual sowthistle that germinates in the early spring will be in full bloom by mid March. The yellow inflorescence is usually open briefly for one day and then only at dawn. A single annual sowthistle plant may produce up to 8 000 seeds The pappus at the top of each small seed allows seeds to be easily distributed by wind. Seeds are long-lived.

Management Approaches

As an annual management should focus on preventing flowering.

Biological Control

Sowthistle species S. arvensis, S. asper and S. oleraceus have been the target of biological control in Canada. And there is research on plant pathogens for use as biological control agents in Australia, but there are no biological control agents available in the United States at this time.

For herbicide recommendations for specific grain rotations and weeds in Montana, please see the MSU Herbicide Chooser Tool.

Mechanical and Cultural Control

Tilling can control annual sowthistle.

Chemical Control

A number of chemical control options are available for annual sowthistle. It is important to verify which species of sowthistle is present because herbicides that work for one may not be effective for the other common species.

Examples of herbicides that can be used to manage annual sowthistle

Consult herbicide labels for additional rate, application, and safety information. Additional herbicide information can be found at http://www.greenbook.net.

Herbicide Active Ingredient trade name	Mode of Action	Product per Acre	Application Time or Growth Stage
Alfalfa
Diuron	Inhibition of photosynthesis at photosystem II
*Karmex		2 - 3 pounds	Treat only vigorous, healthy stands of alfalfa that have been established for at least one full growing season. Do not apply to seedling alfalfa nor to alfalfa/grass mixtures. See label for specific restrictions in Idaho.
Peas and Lentils
Glyphosate	Inhibition of EPSP synthase
*Roundup Original		26 ounces	This product may be applied as an over-the-top broadcast spray or as a spot treatment to control labeled weeds in dry peas and lentils. Allow a minimum of 14 days between application and harvest. Apply when sowthistle is less than 6 inches tall.
Grass Grown for Seed
Clopyralid	Action like indole acetic acid (synthetic auxins)
*Stinger		0.3 - 0.6 pints	Apply when sowthistle between rosette to bud stage. Apply only to established grasses before the boot stage.
Pasture, Rangeland, and Grass
Dicamba; 2,4-D	Action like indole acetic acid (synthetic auxins)
*Weedmaster		1 - 2 pints	Apply when sowthistle is between the rosette and bolting stage.
Barley and Wheat
2,4-D; clopyralid	Action like indole acetic acid (synthetic auxins)
*Curtail		2 - 2.6 pints	Apply Curtail in the spring to actively growing wheat or barley once 4 leaves have unfolded on the main stem and tillering has begun up to the jointing stage (first node of main stem detectable). To control or suppress listed weeds, make application after maximum emergence of the target weeds but before they exceed 3 inches in height.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.

References

For more information and images please visit IPM Bugwood. http://www.ipmimages.org/search/action.cfm?q=annual%20sowthistle&Start=1&results=20