Tropical Milkweed: To Plant it or Not, it’s Not a Simple Question

Dara Satterfield SM

Dara Satterfield, PhD Candidate at the University of Georgia, is studying Monarch butterflies and OE. Courtesy photo

Graduate student Dara Satterfield came to town in late January for the second time in 12 months to take the pulse of the Monarch butterfly population at the San Antonio River Museum Reach Milkweed Patch.  There, dozens of Tropical milkweed plants play year round host to Monarch butterflies.   Satterfield works closely with local volunteers like Mary Kennedy and Mobi Warren of the Monarch Larvae Monitoring Project (MLMP), a citizen scientist program, to monitor milkweed patches far and wide for egg, caterpillar, chrysalis and butterfly action that might shed light on the state of the Monarch butterfly migration.

Monarch on Tropical Milkweed

Monarch butterflies LOVE Tropical milkweed. But is it appropriate to plant it? Photo by Monika Maeckle

Satterfield, like other scientists, believes the increased availability of  Asclepias curassavica, commonly known as Tropical milkweed, coupled with our warmer winters, may have an unhealthy impact on Monarch butterflies and their migration.   The science is undetermined on that question.

A native of  Marietta, Georgia, Satterfield attends the University of Georgia where she is a PhD candidate whose dissertation focuses on the relationship between migration and infectious disease in wildlife.  Monarchs are her species focus.  Satterfield works closely with Monarch scientist Dr. Sonia Altizer, the foremost expert in the country on Ophryocystis elektroscirrha, or OE. The unpronouceable protozoan disease infects Monarchs and other milkweed feeders, often resulting in butterfly crippling or death.

Dara Satterfield

Dara Satterfield checks Monarch butterflies at the San Antonio River Museum Reach Milkweed Patch for OE.           Photo by Monika Maeckle

As winters get warmer, Asclepias curassavica, the only milkweed species commercially available, is less likely to die back in winter. Some scientists hypothesize that A. curassavica entices Monarchs to forego migration and winter in the U.S. This could create an unhealthy hotbed of lingering OE spores for caterpillars and butterflies that remain in the local area.   Since the spores transfer from creature to creature via physical contact with each other or the plants on which they rest or eat, scientists worry that local OE-infested Monarchs will infect and breed with populations that are passing through, possibly jeopardizing the migration.

The situation exacerbates an already serious decline in the Monarch migration.  Drought, genetically modified crops, late summer wildfires, and generally inhospitable conditions pose multiple threats to Monarchs and their migration.   It’s likely that 2012 will be the worst year, numbers wise, in Monarch butterfly migration history since records have been kept.

“Monarchs are famous for this migration so when we see what appears to be a break in their migratory pattern, we want to know why and what the implications are,” said Satterfield.

OE Spores with Monarch Butterfly Scales

Eeeew! OE spores look like little footballs next to Monarch Butterfly Scales–photo courtesy of MLMP

But butterfly breeders and enthusiasts argue that OE is like staphylococcus–present in the general population and becoming a threat only under stressed circumstances. Organizations like the International Butterfly Breeders Association promote best practices for limiting OE in captive environments through education of its membership and seminars on managing and limiting its presence.  And yet others believe that OE is simply a part of the evolutionary cycle, killing those butterflies less fit than others.

For butterfly hobbyists and gardeners, the “curassavica question” presents a quandary:  should we be planting Tropical milkweed or not?

“This is a very sensitive subject in the Monarch world,”  said Satterfield.   “We just don’t have the data right now.” It will take three or four more years to complete Satterfield’s research.   She advises that natives are always better–which is true, IF you can find them and meet their persnickety growing needs.   Organizations like Monarch Watch and the Xerces Society‘s have launched milkweed restoration campaigns, but wide availability of native stock is still a dream.

If you DO plant curassavica, many scientists suggest cutting it to the ground in winter–unless yours is a research site like the Milkweed Patch on the San Antonio River Museum Reach.  Scientists encouraged the City of San Antonio and San Antonio River Authority to leave our milkweed patch alone as an experiment.   Interestingly, the San Antonio patch brags a lower incidence of OE (15%) than in other monitoring sites observed (47%) by the Monarch Larvae Monitoring Project.   The 47% figure is SIX TIMES the rate of OE in Monarchs that migrate to Mexico.

Satterfield suggested that a deluge of milkweed beetles at the Patch this winter decimated not only the foliage, but OE spores.  The hungry orange-and-black bugs pruned much of the diseased growth, creating a better balance for the butterflies. Apparently Mother Nature has her own way of managing the OE problem.

Milkweed beetles have defoliated the Milkweed Patch. But aren't they cute?

Mother Nature on the case: Milkweed beetles defoliated the Milkweed Patch last spring, cleaning out OE spores in the process. Photo by Monika Maeckle

“This may have removed any OE spores on the milkweed plants, which probably helped to keep the prevalence of OE low this year,” said Satterfield. She added that since our Milkweed Patch is further inland and enjoys cooler temperatures than coastal situations in Houston and Florida, the Monarch population was lower and perhaps more hearty.

In the meantime, gardeners are left to make their own calls.   Is it better to have a questionable milkweed source in your yard to provide Monarchs with nectar and host plant, or not?  

Let’s see: Tropical milkweed is easy to grow, widely available, prolific bloomer, favorite host plant for Monarchs and a great nectar source for all butterflies.   I know where I come down on that.   You’ll see Tropical milkweed in my yard.   But I’ll be sure to keep it out of wildscapes and ranch situations, and slash it to the ground in the winter.  

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12 thoughts on “Tropical Milkweed: To Plant it or Not, it’s Not a Simple Question

  1. I live in northern Florida and usually, the non-native milkweed is frozen to the ground each winter.
    The larvae of a tussock moth eats most of the new growth of A. curassavica in my yard each “spring” before Monarchs or Queens have a chance to oviposite. I wonder if this helps keep the spread of Ophryocystis elektroscirrha in check.
    A. humistrata grows along the roadside near my home but when I plant its seeds nothing comes up.

  2. Thank you for another well written, thought provoking article. The question of whether to plant tropical milkweed is difficult indeed. Here in South Carolina we are working with a nursery to raise indigenous milkweed but without success. So rather than have nothing, I will plant some tropical. Like you, I’ll cut it back.

  3. Pingback: The Milkweed & Monarch Situation – Links & Resources | The Roaming Naturalist

  4. Informative article, but no definitive answer. As far as common milkweed…although I have lots of seeds each year, I have not had any germinate that I have tried to grow. Instead I transplant them. Once established they send out lots of underground roots which produce new plants. They are invasive so it is a good idea to put them where they can spread without being a problem. I also have swamp milkweed which is native. At times I have supplemented with tropical milkweed in pots, but it is good to make those you purchase are free of herbicides…topical or systemic.

  5. Both common and swamp milkweed seeds need to be cold treated before planting. I collect fully ripe seed in the fall just before the pod opens on its own. Then lay out damp paper towels and scatter the seed on the towel so that none are touching each other. Roll the damp towel into a sausage and be sure to leave a little tag inside( written in ball point) with the date and variety of milkweed. Make several such rolls until all the seed is wrapped and put the sausages into a plastic bag, then refrigerate for the winter. I have read that 30 days is the minimum. I usually get about 90% germination starting the seed in little peat pots in a tray with clear plastic lid. Remove the lid when the seedlings are touching it. This year I am also trying storing the seed in a container of slightly damp sand, also in the refrigerator. Shake the container from time to time to scratch the seed. Do not let them freeze! Be ready to plant the seeds as soon as you remove them from cold storage. The damp towels may get a little moldy or discolored, but the seeds are usually fine.

    • Thank you for this ingenious and simple method of cold treatment! I’ve been procrastinating my seeds for months since I didn’t want to face the convoluted process of packing each type into separate baggies of moistened potting medium into the fridge.
      This is so much more straightforward and is a wonderful idea.

  6. Pingback: Is Tropical Milkweed Killing Monarch Butterflies- Grow or No?

  7. I live in South Florida.

    So try to understand, every American gardening guide/book/blog/website is pretty much geared around more temperate regions that have “seasons” such as “winter, summer, spring,” and so on as opposed to “hot season, hotter season, rainy season, post-rainy-hot season, and hurricane season” like we have here.

    So I’m going to plant curassavica without the slightest remorse whatsoever. The only question I have, is what to do with a plant that has been stripped bare to where the caterpillars are munching on bare stalks and there are still some fifteen to twenty that still need to eat?

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