Confusion reigns for gardeners and Monarch butterfly enthusiasts trying to “do the right thing” managing their late season milkweed, the host plant of Monarch butterflies.
Monarch laying eggs on Swamp milkweed, Asclepias incarnata, in downtown San Antonio November 15, 2015. Photo by Monika Mae
For the last few years, scientists like doctoral student Dara Satterfield and Dr. Sonia Altizer of the University of Georgia as well as renown Monarch scientist Dr. Lincoln Brower have recommended slashing Tropical milkweed, Aslcepias curassavica, to the ground late in the season. Studies suggest that the year-round availability of Tropical milkweed makes Monarchs more prone to contracting Ophryocystis elektroscirrha, a debilitating protozoan parasite commonly known in Monarch butterfly circles as OE.
Until recently, Tropical milkweed, technically nonnative, has been the only host plant available for butterfly gardeners hoping to lure the migrating butterflies to their yards. The reliable bloomer will thrive year-round in warmer and coastal climates, especially in Texas and Florida. Scientists believe this year-round availability creates a hotbed of nasty OE spores and spreads the disease. Its presence can also encourage Monarch butterflies to break their diapause–or temporarily suspended non reproductive state–and lay eggs, thus unable to complete their migration to Mexico.
No doubt about it: Monarch caterpillars LOVE Tropical milkweed. Photo taken 11/24/2015 by Monika Maeckle
But now, for the first time ever, native milkweeds are more available. And judging from the government funding pouring in to milkweed cultivation and the valiant Monarch butterfly habitat conservation effort, even MORE milkweeds will be coming to market soon. Gardeners will soon have choices beyond Tropical milkweed.
“Plant only species of milkweed that are native to your region, whenever possible.”
That’s what the Monarch Joint Venture OE Fact sheet advises pollinator gardeners like me and you.
We did that. And like good stewards, we’ve been cutting Tropical milkweed to the ground late in the season.
But guess what? Those native milkweeds, which have recently become available because of all the attention on Monarch habitat restoration, are thriving late in the season, too.
Egg found on Texana milkweed, Aslcepias texana, 11/19/2015. Not sure if it’s a Queen or monarch (and it hasn’t hatched yet.) Photo by Monika Maeckle
In my yard right now, for example, I have
- Asclepias texana, Texana milkweed
- Asclepias incarnata, Swamp milkweed
- Aslepias curassavica Tropical milkweed
- Aslcepias tuberosa Butterfly weed
- Asclepias oenotheroides, Zizotes milkweed
- Matelea reticulata, Pearl Milkweed vine.
I sought out these various milkweeds at native plant sales, the Ladybird Johnson Wildflower Center, from our family’s Llano River ranch. I also traded seeds with other pollinator fans, friends and butterfly breeders. At this moment, all but those I’ve cut back (tuberosa and curassavica) still flaunt green foliage, days before Thanksgiving.
Should I cut these native milkweeds to the ground as well?
The theory of OE spores building up over the season, possibly infecting migrating Monarchs would seem to hold true for other milkweeds available late in the year, not just Tropical milkweed.
“You’re right that it’s less about the plant itself and more about the seasonality of the plant,” wrote Satterfield via email. “Any plant that grows 365 days a year in the southern U.S. and supports Monarchs year-round could lead to high levels of disease, as we understand it.”
Drawback to cutting back native milkweeds: we then can’t harvest the seedpods. Photo by Monika Maeckle
“My personal leaning is that if the species are native, they don’t need to be cut back on a regular basis,” said Dr. Altizer via email. “Any natives that routinely remain in lush green foliage into the fall and winter are likely going to be rare species, or it will be a rare year when this happens, whereas with the Tropical milkweed, these commonly remain in green foliage until they are hit by a hard frost or cut back.”
Dr. Lincoln Brower, always the purist, suggests even cutting late season nectar plants back–if they are growing in close proximity to Tropical milkweed.
“I have given some thought to your question of whether nectar sources might accumulate OE spores,” wrote Dr. Brower via email. “I think the answer to this is one of probability and proximity to curassavica [Tropical milkweed]. I think that nectar sources are so diverse and abundant in the natural environment that the probability of Monarchs infecting the plants with spores is very small. …unless the nectar plant is growing adjacent to curassavica. Again, yank it out.”
Confused? You’re not the only one.
Mary Kennedy, volunteer at the Monarch Larvae Monitoring Project
Mary Kennedy, a longtime Monarch Larvae Monitoring Project volunteer and trainer said she is no longer going to advise folks to cut back their Tropical milkweed. “If milkweed is on the ground late in the season, I don’t see why it makes any difference what species it is,” said Kennedy, a former science teacher. “Grow up kids, and make your own decisions.”
One drawback to cutting milkweeds back late in the season is that we then are unable to harvest the seeds. I cut back a patch of Swamp milkweed in August as it was riddled with aphids and gangly. The plants failed to produce any more flowers; thus, no seeds have been harvested from that patch to propagate future native milkweeds.
Satterfield insisted that the scientists’ statements are “still correct and not mutually exclusive.”
Swamp milkweed in the “wild” of the Llano River, 11/21/2015. Photo by Monika Maeckle
“Our research suggests that milkweeds that support Monarch breeding year-round in the U.S. could put Monarchs at higher risk of disease. The milkweeds enabling these non-migratory Monarchs are exotic species, like Tropical milkweed and Family Jewels milkweed. We are not aware of any native species supporting large numbers of Monarch caterpillars during the winter in the Gulf states. So, we do not have any scientific support right now that says we should cut back native milkweeds.”
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