I have 2 Persian Lilac trees growing in large pots. I was hoping you could give me some advice based on the pictures I am attaching. As you can see, on one of the trees, the leaves are in pretty bad shape. When new foilege grows, it only stays green for a short period of time before turning brown like the existing leaves. The second tree was really thriving, but now it, too, is starting to turn brown. I was hoping you might be able to diagnose this for me. Does this appear to be some kind of fungus or is it perhaps a insect causing this (though I am not seeing any)? And based on your diagnosis, what product would you suggest as a remedy? As you can also see from the pictures, the Azaleas growing under the lilac tree are also in bad shape. I have to think, from the proximity, that whatever is causing one is likely causing the other. Thanks, in advance, for any advice you can provide.
Looks very much like Sooty mould. At sometime there must have been greenfly on the plants and the mould has grown on their honeydew, ( basically aphid urine). So first of all deal with the aphids then the mould. There are fungicides which claim to help fight it.
I'd also look carefully for red spider mites. Run a leaf between your fingers and see if a reddish color appears. Check also for tiny webs. There are insecticides for this. Or systemics. Also growing plants on pots can be challenging for them. You have to make sure they are getting adequate water, but not too much. Same with nutrition...enough compost.
I am suspecting that it may be bacterial..something like pseudomonas, although I am sorry that I can’t speak with more certainty. I hope that this is not the case, for effectively treating it is quite difficult. Palustris may well be right with his suspicions. I cannot advise you on what to do because I can’t be sure what it is...however If my plants were presenting with this black manifestation,I would simply remove and destroy all plants showing these signs symptoms. If you are able to establish a correct diagnosis, please let us know as we all cn benefit from this knowledge. Good luck.
