[mdjlucan]

I got some small leaves that are turning yellow a bit anyone know what you his is thank

[Aunt Sally]

When did you plant the plum tree, mdjlucan ? 

Plums can be prone to magnesium deficiency. Which can cause yellowing between the leaf veins.

Have you used a high-potassium fertilisers, such as tomato feed ?  This can cause a magnesium deficiency as potassium is taken up in preference to magnesium.

[mdjlucan]

About 3 to 4 weeks I gave t hem some horse menu  rotted What is the best thing to feed them on

[Aunt Sally]

The horse manure is a good idea. You could use a top dressing of chicken pellets.