A couple of months back, a Vietnamese fellow was visiting, and I was telling him about my bad luck with annona fruit set. He told met that the secret is to put rotting fruit at the base of the tree, which attracts some sort of pollinator. He said that what he does is to simply plant a carambola right next to his annonas (the carambolas fall and rot).
So, I tried it. We now toss all of our fruit scraps at the base of my Lisa atemoya. Right now I have a dozen fruits, and practically every flower is setting. The tree has only been in the ground for about 18 months, so 12 fruits (with more in the way!) is fairly impressive, especially considering that I've never had any luck with annonas in the many years that I've grown them.
I know part of the success is due to excellent car by Har in addition to the fact that this is a tree grafted by Zill's HPP and is on cherimoya rootstock.
Has anybody else had similar experiences?