Noxious Weeds Profile - Milkweed spp.

Author:	Mike Cowbrough - Chief Weed Inspector Ontario Weeds Act/OMAFRA
Creation Date:	March 2003
Last Reviewed:	28 December 2006

English - common milkweed, (also green, swamp, and whorled milkweed species)
French - asclépiade commune (asclépiade a fleurs vertes, asclépiade incarnate and asclépiade verticillée)
Latin - Asclepias syriaca L., Asclepias viridiflora Raf. Asclepias incarnata L., Asclepias verticillata L.

Pub 505 - Milkweed species are generally thought to be poisonous to livestock. Pub 505 suggests that there is some evidence to suggest that common milkweed is toxic, and that other species are highly toxic.
NE Weeds - not mentioned
Canadian Poison Plant - Canadian Poison Plant - This plant has poisoned sheep in the eastern United States. The plant contains cardiac glycosides, which are toxic to animals (Reynard and Norton, Joubert 1989). (A dozen sheep died after ingesting large amounts of common milkweed in Maryland. The plants, which were almost the only vegetation available during a drought, are normally distasteful to livestock (Reynard and Norton 1942). )
Cornell Poison Plant - not listed
Indiana Toxic Plants: TOXICITY RATING: Low to moderate. Milkweeds are unpalatable, and have variable toxicities. Death is not likely unless large quantities are consumed. ANIMALS AFFECTED: All animals may be affected. Sheep are most at risk, but cattle, goats, horses, poultry, and pets are also at risk. DANGEROUS PARTS OF PLANT: Stems, leaves, roots. CLASS OF SIGNS: Gastrointestinal irritation (primarily vomiting and diarrhea), incoordination, tremors, heart problems, respiratory difficulty, death.

Common milkweed occurs throughout Ontario in pastures, waste areas, roadsides, and cultivated fields. Grows best in open areas. Swamp milkweed occurs mostly in wet habitats of swamps and ditches. Green milkweed is native to coarse soils. Whorled milkweed occurs in dry open areas. Swamp and whorled milkweed relatively rare compared to other milkweed species.

Glyphosate at medium to high rates (Roundup Ready crops) at bud to early bloom stage, tolerant to 2,4-D, intermediate to dicamba. Listed on Roundup label but not on 2,4-D or Banvel labels. Apply herbicide at early bud (flowers mid summer) or in early fall. Repeated mowing at 21 day intervals can be an effective control. A single cutting will stimulate the sprouting of underground root buds. Repeated cutting prior to fruit (pod) formation will reduce root reserves.