I've always heard dormant oil for scale. Its cheap, I'd try it.

Scale is a leader cause of death for peach trees in Texas, according to Texas A&M. The recommendation is to use dormant oil on the entire tree. Some apply twice, once in early fall and the other in late winter. I usually also mix copper with it. Copper helps with brown rot and canker. I spray with dormant oil each year and have had good luck.

Scale is one of those insect pests that really should be treated. They can seriously weaken a tree and they easily migrate to other plants.

If it is a hard shelled scale, spraying with dormant oil won't have much of an impact - that shelled surface makes them pretty much impervious to the spray. It is best to treat these when they are in a far more vulnerable instar stage. And to know when that is, you need to identify the kind of scale - there are dozens.

Check to see if these have a hard shell and then post clear, close up photos for an ID. If a soft bodied scale, the dormant oil should work well.

I think its san jose scale. It seems to be soft....

The buds have started to swell a bit. Is it too late to apply the oil this weekend. I have some that i used for other plants but have been to lazy to apply it on the plum tree.

It should be fine. Most people like to spray dormant oil and copper at bud swell to help control scale and brown rot. I did spray a peach tree that was just leafing out and it did not burn the leaves.

As long as none of the buds have opened, it is still OK to do a dormant spray. There are also all-season horticultural oils that can be sprayed at any time.

Please post an image of the scale.

Its dark out now. I will get one tomorrow.

What happens if you spray a tree after the buds have opened?

We've got scale in our yard pretty bad on our long lived basil bush, tangerine tree, and now young figs...it seems to stay off of everything else. The figs are the only thing that seem to show stress from it. So far, they have stayed off of my young stone fruit trees. Hopefully it'll stay that way. Anyhow, I bought some horticultural oil to spray on the figs this year.