When you have a Japanese beetle infestation on your fruit trees, one option is to use commercial pesticides like diazinon or pyrethrin. If this is okay with you, follow the manufacturer's directions for application. Many people don't want to apply pesticides to fruits they will be eating, so here is another method to get rid of Japanese beetles on your fruit trees.
Mix up a beetle-repelling spray. This will kill some of your beetles and drive more away. Crush or chop four cloves of garlic and two hot peppers and mix them with a gallon of warm water. You can multiply this by as many gallons of water as you think you will need for your number of fruit trees.
Let the garlic mixture sit for a day. Strain out the crushed garlic and peppers, and add a tablespoon of corn oil and four or five drops of dish soap to each gallon of spray. Mix this well for a soapy garlic concoction.
Spray this onto the infested trees. You can use a hand spray bottle and a ladder if this will allow you to reach the whole tree, or you can use a tree sprayer if it is available. Garden and pest-control companies often have these.
Apply again if needed. Check your trees later in the day for beetles, and spray again the next day if there are still some in evidence. You may want to hand-pick off any remaining beetles if there are few enough. If you do, drop them in a pail of soapy water to kill them.
Once the beetles are gone, cover your trees in fine netting. This prevents other Japanese beetles from infesting your trees if they come to the area, as it restricts their access to the food supply of leaves and fruit.