There have been a number of questions in the MEI group about phytoplasma, or "milkweed yellows'.
This is the best explanation I can come up with after an extensive search. It comes from this .pdf
https://monarchjointventure.org/images/uploads/mlmp/mlmp_update_2014_fall.pdf
 |
| Photo courtesy of Julie Ross, MEI member |
Phytoplasmas are bacteria; they do not have a cell wall and are enclosed by a single membrane. They cause diseases in plants and are spread by insect vectors (primarily leafhoppers).
Leafhoppers aren't the only insect that can spread phytoplasma, but most of the known vectors are in the insect order Hemiptera. Their piercing/sucking mouthparts allow them to feed on the phloem of plants, where phytoplasmas live. These phloem-feeding insect vectors can transfer diseases such as milkweed yellows phytoplasma by feeding on an infected plant, allowing an incubation period during which the phytoplasma cells replicate and eventually reach the insect’s salivary glands, and then moving to a healthy plant and injecting phytoplasma cells into it during feeding.
How do you know if your milkweed has a phytoplasma disease?
There are a few symptoms to look for, according to the Phytoplasma Resource Center found on the USDA Agricultural Research Service website:
- Phyllody—development of leaf-like growths in place of normal flower parts
- Virescence—development of green color in place of normal flower color
- Witches Broom—abnormal, excessive proliferation of axillary shoots resulting in a broom-like growth
- Yellowing—leaves lose normal green color, becoming yellow
- Little leaf—development of abnormally small leaves
- Proliferation—abnormal growth of numerous stems
- Necrosis—death of cells and/or tissues - Dieback
- death of branches
- Stunting—overall reduction of plant height
- Bunch top—shortening of internodes at and near the tip of a branch, resulting in bunched growth at the end of the branch
 |
| Photo courtesy of Julie Ross, MEI member |
What should you do if you suspect phytoplasma in your milkweed patch?
Since the disease is spread by insect vectors, one way to get phytoplasma under control is to quickly and effectively eliminate any milkweeds suspected of phytoplasma, at the first sign of disease. By digging out an infected plant, you reduce the chances of other insects feeding on that plant and becoming vectors of the disease.
Debbie Jackson, Monarch Watch Conservation Specialist, says ...
Milkweed can be affected by a killer disease called phytoplasm. Signs: the leaves are wrinkled, like they're shrunken between the leaf veins, tissue near the veins is yellow, the plants are shorter and the stems are clustered too closely together than normal.
- Please try to get
all the root out to kill it. The
entire milkweed planting may be affected because it is spread through the
rhizome root system. You can't save part of it, you have to remove it
all. The largest one I've seen was about 50' in diameter.
- If you have monarch caterpillars to feed, you can dig it up, cut off the leaves, rinse
& pat them dry, then refrigerate the leaves for up to 2-3 weeks to use for food.
 |
| Photo from Debbie Jackson |
pencil-thin stems packed together radiating from a node on the rhizome.
- Phyto kills milkweed and there is no cure. Leafhoppers suck up the disease and transfer it as they bite into other plants. Prevent it's spread by removing the affected plants. A friend of mine saw a clone of 200 common milkweeds die in 2 years from phytoplasm!
- It has also been suggested to cover the milkweed plants with a mesh
or tulle cover to avoid leaf hoppers getting to it and spreading the
disease.
View more photos of phytoplasma at
https://squirrelworking.ca/plants/milkweed-yellows-phytoplasma/
You can also run a search for milkweed phytoplasma and then click "images" to see photos.
