White Flies on my Italian Plum

I didn't realize Italian plums were so susceptible to whiteflies.  The brand new growth seems to be covered with them. And they are sucking the life out of my young fruit tree. Strangely enough it's not affecting my shiro plum.

I can't stand the site of these flies. And spraying them with just my hose doesn't seem to solve the problem.

There are only a couple of plums on the tree this year. So I went ahead and gave it the full treatment.

1. I Sprayed the entire tree with Sevin
2. I cut off all the affected branches
3. I covered the tree with Diatomaceous earth
4. I've researched that applying worm castings to the base of the plant will make the taste of the tree unbearable to the whiteflies.
5. I hung 4 large yellow stick traps on the tree to add the last line of defense.

Hopefully this works, if it doesn't I may have to replace the tree with something more bug resistant.

How do you get rid of whiteflies?