Wasps, flies and hover flies on plum tree

Question

We are having a problem with wasps, flies and hover flies on our plum tree. They don’t appear to be attacking the tree but there are thousands of them. The tree looks like it now has a film over to one side?

Answer 1

You haven't mentioned any other symptoms, like leaves curling, but I would bet that your tree has an infestation of plum aphids or some other small insect that wasps and flies like to feast upon. Of course, if the tree is bearing fruit, that, too, may be attracting them. It sounds like you need to treat the tree with horticultural oil. These articles should help:

https://www.gardeningknowhow.com/edible/fruits/fegen/wasps-in-fruit-trees.htm
https://www.gardeningknowhow.com/edible/fruits/plum/control-leaf-curl-plum-aphids.htm