Hi I had the same problem. I increased the water and twice a week i hand watered it with a gallon of water (extra). In a week there was a marked difference and the plant just sarted to bloom and the leaves got their happy and glossy look back. Padma

It could be all the rain. I have some plants that have some yellowing of the leaves. Hopefully when they dry out, they'll green up again. Purple-leafed plum trees are also susceptible to cotton root rot which can kill any tree within a couple weeks. There isn't anything you can do about this. The excess moisture could have brought this on. Make sure the root flare is visible - not below the soil surface too.

It looks like bacteria spot. If it is bacteria spot, the spots will turn to holes. Not much you can do but get disease resistant varieties. Some of mine get it every year but usually it is in the late summer. I doubt the spray had anything to do with it. The tree looks healthy. When you sprayed for ants you probably also had aphids. The ants like to protect the aphids so they can eat the honey dew that the aphids secrete. With stone fruit the biggest problems are brown rot, worms (oriental tip moth and plum curculio) and scale. The brown rot can be controlled with fungicides. Tip moth and plum curculio can be controlled by insecticides sprayed when you see the fruits bitten by the beetles. Scale can be controlled by a dormant oil spray in the winter, and some add copper to the last dormant oil spray to help control brown rot and bacteria canker. It is easier to have 4 separate trees than a multigraft, but since it was a gift not much you could have done about that. You will have to prune to keep all the four branches about the same size so one does not dominate the others.

I posted this in the Fruit and Orchard forum, but since I live in Charlotte, I wanted to post it here too. I have a multi-graft stone fruit. It was doing so well...until I went outside today and the plum leaves are covered with brown spots and some of the young, small leaves are yellowing and falling off. The only thing I have done since planting is spray the tree with Garden Safe Garden Insect Killer. I don't know what to do- I have never grown this type of fruit tree before. Photos attached and sorry they are huge.