HPIPM:Common milkweed

Taxonomy

Domain	Eukarya
Kingdom	Plantae
Phylum	Magnoliophyta
Class	Magnoliopsida
Superorder	Asteranae
Order	Gentianales
Family	Apocynaceae
Subfamily	Asclepiadoideae
Tribe	Asclepiadeae
Genus	Asclepias

Scientific Name

Asclepias speciosa

Common Name

showy milkweed

Common milkweed (Asclepias syriaca)

Compiled by: Jane mangold, Montana State University

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

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

http://www.gov.mb.ca/agriculture/crops/weeds/fab50s00.html

http://ipm.ppws.vt.edu/scott/weed_id/ascsy.htm

http://www.illinoiswildflowers.info/weeds/plants/cm_milkweed.htm

Identification and Life Cycle

Common milkweed (Asclepias syriaca) is perennial weed in the milkweed family (Asclepiadaceae). Common milkweed grows from a deep rhizome. Stems are hairy and usually solitary from a simple to branched and thickened base. Stems reach heights of 2 to 6 1/2 feet. Leaves are opposite, broadly ovate, and 4 to 8 inches long and 2 to 4 1/2 inches wide. Leaves are sparsely hairy on the upper surface and very hairy on the bottom surface. Flowers develop in the upper leaf axils. Common milkweed has 20 – 130 flowers per inflorescence. Green to purple-tinged flowers are small (1/2 to 3/4 inches), have five petals, and are topped with a crown of five erect lobes that are rose to purple in color. Fruits are spindle-shaped follicles covered with soft hairs. Seeds are small and round (1/4 inch) with a tuft of hairs.

Habitats

Common milkweed grows in sandy, clayey, or rocky calcareous soils. It occurs along the banks or flood plains of lakes, ponds, and waterways, as well as in prairies, forest margins, roadsides, and waste places. Common milkweed also occurs as scattered plants in cultivated fields and pastures.

Impacts

Common milkweed contains cardiac glycosides that are poisonous to humans and livestock causing dullness, weakness, bloating, inability to walk, high body temperature, difficulty breathing, dilated pupils, spasms, and coma when ingested. Common milkweed can also lead to yield losses in crops.

Biology and Ecology

Common milkweed reproduces from both seeds and buds at the base of stems or along lateral roots. Seedlings flower in their second year. New plants can generate from cut pieces of rhizome if buds are present. Buds usually occur every 2 inches. Aerial shoots emerge from rhizome buds in April and May. Growth begins with the arrival of warmer weather and continues throughout the summer. Flowering occurs in June and July. Common milkweed is self fertile and pollinated by wasps and bees. Only 2% of flowers produce mature pods and on average mature plants produce 4 – 6 seeds pods each with each pod containing 150 – 425 seeds. Seed pods split open in early fall and mature seeds are dispersed by wind. Seeds are typically dormant for one year before germination occurs. Seedlings produce buds on their roots within 18 – 21 days of germination. Roots penetrate the soil up to 3 feet.

Management Approaches

Control of common milkweed can be difficult due to the ability of the plant to regenerate from buds on underground roots.

Biological Control

There are no biological control agents available for common milkweed.

Mechanical and Cultural Control

Cutting common milkweed stems stimulates regrowth from buds on underground roots and tilling can spread root pieces within a field. If root pieces contain buds, they can grow into new plants. For mechanical control to be effective, it must be performed regularly over an extended period of time.

Chemical Control

A number of chemical control options are available for common milkweed.

Examples of herbicides that can be used to manage Common milkweed

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
STS/RR or STS Soybeans
Chlorimuron; thifensulfuron	Inhibition of acetolacetate synthase ALS (acetohydroxyacid synthase AHAS)
*Synchrony XP		0.4 – 1.1 ounces	Apply when milkweed is 4 – 6 inches tall.
Alfalfa
Glyphosate	Inhibition of EPSP synthase
*Roundup Ultra Dry		3.5 pounds	Apply before planting alfalfa when most milkweed plants have reached the late bud to late flower stage.
Grass Grown for Seed
Glyphosate	Inhibition of EPSP synthase
*Roundup Ultra Dry		3.5 pounds	May be applied preplant, preemergence, at-planting, during site preparation. Apply to actively growing milkweed plants at the late bud to flower stage of growth.
Fallow
2,4-D	Action like indole acetic acid (synthetic auxins)
*Weedmaster		2 - 4 pints	Apply from preflower to flower. May require repeat applications.
Corn
Dicamba	Action like indole acetic acid (synthetic auxins)
*Banvel		0.5 - 1.5 pints	Apply when weeds are actively growing.

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=common%20milkweed&Start=1&results=38