01 Aug Pruning Tropical Milkweed in the Fall – Imperative for Monarch Butterfly Health
Tropical Milkweed has been on the market quite a few years and, as a result, is prolific in Orange County. It doesn’t die back in the fall like native milkweed, but continues to get leaves year round.
This creates a serious health issue for individual monarch butterflies and for the population as a whole. There is a microscopic parasite called O.e. that is naturally found on milkweed. Butterflies get it by landing on plants with it and caterpillars get it by eating leaves with O.e. They then emerge as butterflies with O.e. on their abdomens that gets spread to milkweed wherever they drink nectar or lay eggs. One season of O.e. on a plant is not a problem typically. However, O.e. on native milkweed dies off in the fall with the plant. Tropical will continue to accumulate O.e. if not cut back and in 2 to 3 years will have a dangerous amount on it. The amount then ingested by caterpillars will cause the emergent butterfly to have deformities in the wings and not be able to fly, dying in a couple days from starvation.
The second concern if for the monarch population as a whole. If monarchs emerge in early November and smell milkweed leaves, they will sexually mature and stay here rather than migrate to central coast California. This weakens the overall population as less able monarchs die off during the migration.
Therefore, it is CRITICAL to PRUNE TOPICAL MILKWEED at Halloween down to 10-12″ tall and strip off all the leaves, mimicking die back and removing all the O.e. for the season.