Sue, Welcome to Goy. Are there Aphids or capsid bugs on the leaves.

treated for blackfly weeks previous cant see any aphids,wasps small flies and
small wasp type on tree at moment have trapped hundreds of wasps!!!
Sue

The wasps are eating the small black flies and possibly their eggs. They will be in the black deposit on the leaves. Leave the wasps to do their work.

can see where your coming from,but the soooty look on leaves has only appeared since wasps have arrived also some wasps on ground that seem to be dopey (drunk)!! is it not possible to spray tree, as it is close to the house,also visiting grandchildren.
Sue

Can you find the nest or nests? which can be treated with Nipon. The drunk wasps must be eating rotten fruit, coming to the tree for another part of their diet, watch the path in which they fly, it may lead you to the nest. Washing the tree with a hosepipe in the evening may get the black off the leaves. Don't get stung.

many thanks for comments .If anyone has a thought about this problem please
contact thank you .Sue