Jeannie, check around the base of the plant. Look at the stems where they enter the soil and look for minute damage. Maybe shine a flashlight down under the plant at the base of the stems for a good close look. Sometimes chewing insects will feed right at the soil line, often at night and we don't notice them or the damage until the plant begins to react. If something has chewed around the base of the stem, the stem can't take up moisture, quickly wilts and dies. The brown stem looks like it also has a bit of powdery mildew or some type of fungus growth. This might be because the stem was under stress already and weakened, allowing this to quickly take hold or it may have taken hold after the stem died.

This is just a guess but for a stem to die this quickly, while other parts of the plant look healthy, this is what I'd look for. If you can't see anything unusual, try sprinkling a bit of white flour on the soil around the plant right next to the stems and see if that allows you to spot anything suspicious the next morning. :-)

Good luck.

Mary

Plus the plant proliferates and at a much faster rate than any dieback you might experience. Personally I don't mind b/c I want a butterfly garden plus easy to pull.

Thanks for the suggestions. I've check the plant so often and never found anything around the base or in the soil around the base. I did at one time see a brown beetle looking bug on the stem and under where it was sitting was brown (coincidence or it could be what's making the stem brown and then die back). Who knows.

A few weeks ago, I purchased another large milkweed plant and it too has the brown spots on the stem.....I have to watch and cut it back where that spot is or it will kill the whole stem.

Happy Gardening, Jeannie :)

Did anyone ever determine what this is. All my milkweeds have it now

Tropical, Hairy balls and Incarnata (swamp milkweed) seem to be most affected. Starts as a black dot. Sometimes red or yellow center. Spreads, gets in the crevices and I can turn a stem looking for aphids and have it break off in my hand. The pic here is the closest to it I have been able to find on the internet. Last year I lost half my plants to it. Am on track to do so again. Saved some buy cutting it out and hitting it with alcohol. But hard to keep up with over two hundred plants. I kept thinking armored scale (a lot of leaf drop) but find nothing on the internet that looks like it. I used a horticultural oil and some relief but am in north FLorida with rain daily and no end sight. I looked at milkweed weevils, but I rarely see them. Thanks for the feedback any thoughts are appreciated.

P.S. I have many nectar plants and they seem unaffected.