Ventura County Bans Sale of Tropical Milkweed to Protect Monarchs
Because of its role in spreading disease among Western monarch butterflies, tropical milkweed
(Asclepias curassavica) has been classified as a “noxious weed” by the California Department of Food and Agriculture. That led to a June 1 notice of a ban by Ventura County Agricultural Commissioner Ed Williams on its sale by nurseries and other retailers.
The popular yellow-and-red flowered garden plant is a non-native that doesn’t go dormant during the winter, unlike the native narrowleaf milkweed (Asclepias fascicularis). Tropical milkweed harbors a parasite called Ophryocystis elektroscirrha that preys on monarchs. More commonly known as OE, the parasite’s spores are carried on and spread by adult monarchs as they migrate.
As monarch caterpillars hatch and feed on effected plants, they ingest the OE spores and become infected with the parasite. OE infections are linked to reduction in body mass, diminished reproductive success, and, ultimately, shortened lifespans. The sharp declines seen in the Western monarch population since the 1990s are in part due to OE.
Although the newly enacted ban applies only to the retail sale of tropical milkweed, Jackie Nuñez, a spokesperson for Ventura County’s executive offices, says, “Anyone who wishes to remove this plant from their properties is encouraged to do so.”
Image by Kimberly Frantz/Pixabay