This is a pic of my autumn joy sedum (stonecrop). It has done remarkably well for 5 years but this year has stunted growth and has these dark areas; it also seems to have some leaf curl. In the second picture (the close up) you will notice a lot of debris on the foliage- I am not certain how that got there? I don't see any obvious insects or insect damage. Any thoughts are appreciated. Thanks!
Check for aphids. The black substance may be fungal growth on honeydew secreted by aphids. The little white flecks of material on the leaves may be discarded "skins" from the aphids as they pass through larval stages.
If it is indeed aphids, you can wash them off with water from a garden hose directed under the leaves and at all areas of the plant; do it daily for a few days until you see no trace of the aphids.
I agree with altagardener, it is something like whitefly or greenfly, the black sticky substance is caused by the poo the little insects drop onto the plants.
You may also find your inundated with a few hundred little ants that live side by side of the aphids, the ants ward off any predators that would eat the aphids as the ants live off the honey fungus (black stuff) the aphids drop, (nature covers all sorts EH !!!! ) I would go out with hose pipe and glove, gently wash off the black sticky goo, then wash /spray under all the foliage as that's a place insects hide, when they need to hide away. IF it's green or white fly you find, you can squash them dead between your thumb and finger, they don't sting or bite.
I would do this a few days apart and also another treatment for the same is to use washing up soap diluted in water as this has an oil added to prevent dry hands it also kills off the aphids as the oily water prevents them breathing.
If you dont get rid of the flies, they will fly off to lots of other plants and then the problem is spread from one plant to another by the ants, so visious cycle is formed.
Good luck, WeeNel.
These plants are normally as tough as old boots and suffer more from attack by slugs /snails, or aphids that love the nice lush foliage ever earwigs love them but unless the plant is growing in an area that is waterlogged then over watering has never been a problem for me and I live in an area that suffers high rainfall even in summer.
To check for wet soil just stick your finger into the soil and if it's wet then don't water if dry give water, week or damaged plants are more likely to succomb to damage from sap eating insects than a healthy plant, the healthy plants do get eaten but normally withstand a nibble but perhaps not constant attacks.
I see the plant as healthy BUT with a few blotches from black Honeydew as mentioned in the other answers above.
Good Luck. WeeNel.
Jcook45, I don't use chemicals either but to be fare some folks do as a last resort, My bug-bare is when I see the miss use of them, I've known some folks who don't measure the dosage, what's left goes down their drains and probably into the water course and rivers. Here in UK there are talks afoot to try get farmers to use less chemicals as these may be harming the pollinating insects like bee's ect. Watch this space, there are still lot's of investigations going on and all tests are not yet complete. I'm sure we will all here this news when it comes.
Best regards, Weenel.