Loretta,

Thank you for your question. I am consulting with a partner.

It is hard to tell if the black discoloration is ON or IN the leaf surface. This may be a case of wet black mulch or soil getting on the leaf and drying there. Could you try to wash off the black on the leaf surface with a paper towel and a lot of water?

Could you retake the picture after so we can see the result of washing and any progression of markings since 7/31/23?

THANK YOU,

I went out and washed with water and paper towel.  The black stuff does come off.  They are starting to bud now and those don't look healthy either.  Here are updated photos.

Greetings Loretta!

Thank you for your question!

Because there are few things that can cause this picture, we consulted each other.
Your picture appears to depict old aphid bodies, leading us to believe this is Sooty Mold.
An academic page with videos about Sooty Mold from Aphids is here: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74108.html
Here is an excerpt:

Can sooty mold damage plants or other surfaces? Although sooty mold doesn’t infect plants, the mold can indirectly damage the plant by coating the leaves to the point that sunlight can’t reach the leaf surface. Without adequate sunlight, the plant’s ability to carry on photosynthesis is reduced, which can stunt plant growth. Coated leaves also might prematurely age and die, causing premature leaf drop.

Fruits or vegetables that become covered with sooty mold are still edible. Wash off the mold with mild soap and warm water.

MANAGEMENT

When sooty mold is present on any plants or surfaces in the landscape, it indicates there is, or has been, a sucking insect population present in the vicinity. Most plants will tolerate a small insect population and light amounts of sooty mold. Control of sooty mold begins with managing the insect creating the honeydew.

New, tender plant growth is preferred by many sucking insects and may attract them. Check new succulent plant growth for sucking insects like aphids, psyllids, or any of the other insects listed above. In some situations, a strong stream of water can knock off the insects. Fertilize and water properly to keep plants healthy but not growing excessively.

I see aphids on the tender new growth. They can not fly or crawl back up on the plant. A strong hose on plants while you support it with your hand will knock them off. You may need to repeat this.

Though we do not see these now, In the future you could read about other possible harms  to Autumn Joy Sedum which could include:

Autumn Joy Sedum (Hylotelephium x 'Herbstfreude') black leaf spot:
Leaf Spot Septoria sedi Tan to gray round sunken spots on leavesBlack raised dots in the center of mature leaf spotsLeaf tissue around leaf spot turns yellowLower leaves most severely affected

Stem Rot 

Colletotrichum sp.Leaves turn yellow or tan, shrivel and dry upThe base of the stem becomes tan or gray colored and sunkenRaised black dots can sometimes be seen in the sunken area of infected stems.
University of Wisconsin general Septoria treatment all plants:
https://hort.extension.wisc.edu/articles/septoria-leaf-spot/

Greetings Loretta!

Thank you for your question!

Because there are few things that can cause this picture, we consulted each other.
Your picture appears to depict old aphid bodies, leading us to believe this is Sooty Mold.
An academic page with videos about Sooty Mold from Aphids is here: https://ipm.ucanr.edu/PMG/PESTNOTES/pn74108.html
Here is an excerpt:

Can sooty mold damage plants or other surfaces? Although sooty mold doesn’t infect plants, the mold can indirectly damage the plant by coating the leaves to the point that sunlight can’t reach the leaf surface. Without adequate sunlight, the plant’s ability to carry on photosynthesis is reduced, which can stunt plant growth. Coated leaves also might prematurely age and die, causing premature leaf drop.

Fruits or vegetables that become covered with sooty mold are still edible. Wash off the mold with mild soap and warm water.

MANAGEMENT

When sooty mold is present on any plants or surfaces in the landscape, it indicates there is, or has been, a sucking insect population present in the vicinity. Most plants will tolerate a small insect population and light amounts of sooty mold. Control of sooty mold begins with managing the insect creating the honeydew.

New, tender plant growth is preferred by many sucking insects and may attract them. Check new succulent plant growth for sucking insects like aphids, psyllids, or any of the other insects listed above. In some situations, a strong stream of water can knock off the insects. Fertilize and water properly to keep plants healthy but not growing excessively.

I see aphids on the tender new growth. They can not fly or crawl back up on the plant. A strong hose on plants while you support it with your hand will knock them off. You may need to repeat this.

Though we do not see these now, In the future you could read about other possible harms to Autumn Joy Sedum which could include:

Autumn Joy Sedum (Hylotelephium x 'Herbstfreude') black leaf spot:
Leaf Spot Septoria sedi Tan to gray round sunken spots on leavesBlack raised dots in the center of mature leaf spotsLeaf tissue around leaf spot turns yellowLower leaves most severely affected

Stem Rot

Colletotrichum sp.Leaves turn yellow or tan, shrivel and dry upThe base of the stem becomes tan or gray colored and sunkenRaised black dots can sometimes be seen in the sunken area of infected stems.
University of Wisconsin general Septoria treatment all plants:
https://hort.extension.wisc.edu/articles/septoria-leaf-spot/

Thanks for your help.

Loretta,

To be sure of the diagnosis:

Would you please email all the pictures to MSU Plant Diagnostic lab for their opinion? Include details like how you water ( sprinkler or soaker hose?) and any chemicals or fertilizers that have been used within 12- 15 feet of the plants, and describe how you washed the plants.

The email consultation is free of charge. Their email is <personal data hidden>

If the lab needs to analyze a branch sample there is a fee for that. Their website describes how to submit samples, and has the lab contact information."

https://www.canr.msu.edu/pestid/