How can I prevent or minimize my two apple trees setting fruit this year?

There is a product you can spray on them while they are in bloom to prevent fertalization. It's call Florel. But it needs to be sprayed when the tree is in bloom. Unless you're significantly further north than I am, your apple trees have already bloomed this year. Keep it in mind for next year, though.

If you get your hundreds of unwanted apples this year, maybe see if any neighbors are interested in making applesauce or cider. Or if there are farmers who wouldn't mind some free pig food.

The volume of fruit in trees is directly related to soil pH. If you were to tweak that, you could effectively halt its production, however, it may harm the tree. Given its age, I don't think that it would do much harm, other than slow growth a bit, because fruiting is indicative of a healthy tree, but I am not an arborologist. You can also purchase nets that surround the base of the tree, similar to a hammock-like material, and it catches the apples for you, making disposal easier. However, it is certainly not the most elegant solution.

You can not keep the trees from setting fruit. You need to thin the fruit when it is very young to minimize limb breakage, stress to the tree and provide you with larger, better tasting fruit.

http://www.lsuagcenter.com/nr/rdonlyres/069bcd8f-9...

Unless you live in Louisiana ignore the variety recommendations. The rest of the information is generic and applicable to all regions. Do read the section on pruning. Even old trees can be pruned. The information on thinning begins on page 22.

Hope this helps.

Good luck

easy way is when it blooms spray the blooms you do not want to make fruit with white vinegar. it also works if you have a black olive tree that makes a mess every year. spray it with white vinegar when it is in bloom and it will not make olives or will make very little of the fruit