If you still have tropical milkweed in your garden, now is the time to cut these plants down to ground level.
Tropical milkweed (Asclepias curassavica) is a non-native milkweed that becomes a problem when planted in temperate areas, such as Southern California. Because it doesn't die back in winter, a protozoan parasite of monarch butterflies, Ophryocystis elektroscirrha or OE for short, can travel with monarchs visiting the plants and become deposited on leaves. When caterpillars hatch and start eating the plant, they ingest the OE. High OE levels in adult monarchs have been linked to lower migration success in the eastern monarch population, as well as reductions in body mass, lifespan, mating success, and flight ability, according tyo the Xerces Society..
"When native milkweeds die back after blooming, the parasite dies along with them so that each summer’s monarch population feeds on fresh, parasite-free foliage. In contrast, tropical milkweed that remains evergreen through winter allows for OE levels to build up on the plant over time, meaning successive generations of monarch caterpillars feeding on the plant can be exposed to dangerous levels of OE," the Society reports.
So if you can't bear to pull out your pretty, tropical milkweed, please give our Western Monarchs a hand by cutting your plants down to ground level during the fall and winter months.