Thank you for reaching out to ask2.extension

Once sooty mold has established itself, it can be difficult to remove. You can try soaking affected plants in a mixture of water and detergent. In severe cases, you can also try using a fungicide.  Be sure to read and follow all label instructions.

Depending on how badly infected the plant is, you could cut back the infected parts and totally get rid of it-not compost it.  I would suggest putting it into a bag and disposing of it.

Be sure that there is adequate air movement around your plants.

I hope this helps.