You'll need to control the height and control the shape. Figure out how high you want it to be and then cut it back. For my trees, I don't want to have to use ladders so I keep them small. Next is pruning it in an open center (or vase shaped). An open center lets light get into a nice big area (the inside of the "vase") which will allow your fruit to fully ripen. It looks like the lower half of the tree has some nicely placed and angled scaffold branches so you might only have to take out that tall middle branch (one part goes off to the right, the other goes almost straight up)

I thought that it was just a ladybug, but it is so much smaller than the ones I normally see around my house. Those black things are nymphs? They are kind of creepy looking! I think that the picture is making it look as though the green dots are aphids, but those are just little holes in the leaves. Are all aphids green? I saw one little winged creature when I was taking the pictures, but the wings were more of a muted striped color. Thanks.

The red little creature might be spider mites, but, if they are, they are the biggest spider mites I've ever heard of. Best evidence that it's a spider mite, is to see the same insect crawl on something white, and smush it! If you have a long, thin smudge of orange, that used to be a spider mite. Really doesn't matter what it is, I think I know what will kill bad bugs without killing you or your fruit tree, BUT read the label carefully, because it does also kill certain plants, and certain beheficial bugs, too. Neem Oil! I think I got mine at Lowes. Most gardening centers (except Home Depot) sell it. While there, read directions carefully, first, and, one of my favorite things to do is find knowledgable staff. (Still read directions carefully. Hard to tell who is knowledgable, and who isn't, and I'm just giving you info, I learned over the winter, and have just started trying on Sunday, so I'm not an expert either.) If that is the product you decide to use, you'll also want a good sprayer. It has to be deluted, and soak every leaf, top and bottom, on the tree without getting yourself wet. (Direct contact, is bad.) Good luck. I miss the plum tree I grew up with.

It is frustrating when there is no treatment for something, but that is the case with your plum. As Mr. Adrian noted, all prunus species tend to be rather short lived trees, but unless you are trying to grow them in an area unsuited for them there is much you can do in an attempt to extend their life well beyond 10 to 15 years. Gummosis will not kill this tree, but there are other pests and diseases that can. So... Using Tree Tanglefoot or a similar product, follow the instructions and put a band of it around the trunk. This will prevent some insects and caterpillars and will at the same time give you an easy way to monitor pest activity. You can also hang pest traps among the branches. Your County Extension Sevice or state agriculture department can suggest which type would be best for your locality. They can also identify pests and offer treatment suggestions. Keep a close watch for black knot disease and prune out any branches showing early symptoms. Take soil samples and send to either of the places mentioned above. If there is a serious nutritional deficiency, follow their recommendation to correct it. If the tree is growing in grass, get rid of it in a circle at least 4 or 5 feet in diameter. Don't use an herbicide. Instead, put down a reasonably thick layer of newspaper followed by a layer of mulch, keeping it away from the trunk. Keep the tree well-watered during periods of drought. Doing all this does not guarantee a tree that will continue to flourish for 50 years, but it will help and it is possible. I know of 2 local Prunus Okami's - one in my own backyard - which are approaching their 50th years with not much more than benign neglect as a treatment. There are also cherries, plums, and a few peaches still bearing in a nearby orchard that were planted in the 1970's. These, of course, have been regularly sprayed and fertilized.