Q: Is there a product that will kill blooms on a crabapple tree and prevent fruit from growing?

A: Fruit control on small trees is possible if you time it correctly. You can spray with ethepon (click for sources) at bloom to make the flowers drop before they produce fruit.

If the bloom time in spring has passed, you can cause substantial fruit drop by spraying the tree with carbaryl(Sevin). Mix 1 ounce of the 22.5 percent liquid concentrate in a gallon of water and thoroughly spray the tree until it drips. It’s important to spray in the evening, to avoid harming honeybees, and to wear protective clothing while you work. Do the application as soon as possible.

You’ll get best results when the fruit is less than one-half inch in diameter.