Hello and thank you for contacting Ask Extension. I think your sedum has powdery mildew. Symptoms of powdery mildew include:

• White, talcum-like colonies on the leaf surface,
• Chlorotic spots may be present on the leaf surface opposite the colony
• Under favorable conditions colonies enlarge and merge together
• Infection on Sedum causes slightly raised scabby lesions.

Powdery mildew is spread by wind. High relative humidity levels are conducive to powdery mildew development. If possible, reduce the level of humidity by increasing plant spacing to promote air movement. Increase light penetration (sedum like sunlight) and prune out some of the branches to let more air and light in.

Spraying neem oil or a fungicide will prevent the powdery mildew from spreading, but may not do much to heal the existing leaves. Do not use these products when the temperature is about 85 degrees Fahrenheit. Always follow the instructions on the label.

Here are some links to articles about powdery mildew:

https://extension.umn.edu/plant-diseases/powdery-mildew-flower-garden

https://www.canr.msu.edu/resources/powdery-mildew

https://www.extension.purdue.edu/extmedia/BP/BP-5-W.pdf

I also think I might see some mealybugs on your sedum. When I zoom in on your photo it is a little too grainy to make a definite diagnosis. Mealybugs are pink, soft-bodied insects covered with a white, waxy, cottony material. The white “fluff” helps protect them from excessive heat and moisture loss.

If mealybugs are present, you can try to reduce or eliminate infestations by washing off the plants. A moderately strong spray of warm water will dislodge most of the mealy bugs. You can also try wiping the insects and egg masses off the plants with a cotton swab or cloth dipped rubbing alcohol. Test first on a small area of the plant to make sure the alcohol won’t damage the plant. Washing rarely eliminates all the pests, so it is important to check the plants periodically and wash again or use other controls when more are noticed.

Here are some links to publications on mealybugs:

https://www.canr.msu.edu/news/mealybugs_a_common_pest_of_indoor_plants?_ga=2.205630419.<personal data hidden>.<personal data hidden><personal data hidden>.<personal data hidden>#:~:text=With%20smaller%20infestations%2C%20Michigan%20State%20University%20Extension%20advises,make%20sure%20it%20is%20labeled%20for%20indoor%20use

https://hort.extension.wisc.edu/articles/mealybugs-2/

Wooly aphids is another pest that resembles powdery mildew and mealybugs. If you want to know for sure what is bothering your sedum you could send your picture to the Plant and Pest Diagnostic lab at Michigan State University. Their email address is: <personal data hidden> They may ask you to send in a sample. Here is a link to their website. Here you will find information about how to send it your sample plus what their fees are. https://www.canr.msu.edu/pestid/