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Milkweed yellows? #876228
Asked July 07, 2024, 7:42 PM EDT
Hello! I am still pretty new to gardening so I'm hoping you all can help me out. We started a native plant pollinator garden last year and it has been doing well so far. However, I started noticing our swamp milkweed looking strange about a week or so ago. Now our butterfly weed is starting to look similarly. I have a few questions: 1) is this indeed milkweed yellows? 2) do I need to remove all our milkweed plants, or will they still be safe for monarch caterpillars? 3) if they will still be safe for monarchs, will the disease spread to other plants that aren't milkweeds or otherwise cause any issues if left alone? Thank you in advance! We are hoping to keep a good supply of milkweed on our property for the monarchs in the long term.
Merrimack County New Hampshire
Expert Response
Hi Lauren,
thank you for your question! I would say that the combination of distorted leaves and the yellowing/necrosis on the leaves could be symptomatic of milkweed yellows phytoplasma, but may also be from a virus. (the third photo of the butterfly weed has more of a mottled appearance on the leaves, which can more of a virus symptom.) Milkweed yellows is believed to be spread by leafhoppers primarily, but may be other insects also. Milkweed viruses are commonly spread by aphids and cucumber beetle (milkweed is a host for cucumber mosaic virus.)
The most accurate diagnosis would be from our UNH Extension Plant Diagnostic Lab. They accept emailed photos here: <personal data hidden>, as well as tissue samples. More information on how to submit a sample can be found here: https://extension.unh.edu/agriculture-gardens/pest-disease-growing-tools/plant-diagnostic-lab
More information on milkweed yellows can be found here: https://monarchjointventure.org/blog/what-is-milkweed-yellows-phytoplasma
If it is either a phytoplasma or a virus, unfortunately there are no available treatments other than removing the infected plants to prevent further spread of the disease.
Neither phytoplasma nor a milkweed virus can harm the caterpillars, and I don't believe that they are a vector for spreading either disease either.
Accurate diagnosis will determine how transmissible it is to other plant species; this may have to be taken from a plant sample. Milkweed is also susceptible to aster yellows, which is a phytoplasma that affects a very wide range of plant species - https://mastergardener.extension.wisc.edu/files/2015/12/aster_yellows.pdf
I hope that you find this information helpful, but please let me know if you have further questions!
