If you are noticing brown spots on the skin of your apples, it is likely that the fruit of your apple tree has been infested with a worm. The worms are caused by fruit flies that fly around your apple tree laying eggs inside the skin of the fruit. Once the egg has been injected in your apples, it is only days before the maggot will take over your apple, causing it to rotten and fall to the ground. There is not much you can do about the apples that have already been infested. But there are preventive measures you can take to stop the fly from injecting eggs into the fruit of your tree.
Hang yellow sticky trap cards on the branches of your Apple tree. These cards can be purchased from your local garden supply store. The yellow sticky traps contain a sticky substance that will trap the flies as they buzz around your tree.
Because the sticky trap card is outside in the elements, the stickiness of the card will wear off in a few weeks. For that reason you must replace the card every four weeks or when it is full of flies, whichever comes first.
Spray your apple tree with an insecticide. This insecticide can be purchased from your local garden supplier. In order for the insecticide to work efficiently you must spray it from late June to October, which is when the fruit flies have their greatest activity.
Spray "Dormant Oil" on the apple tree right before the tree begins to bud, which is generally late winter or early Spring. The dormant oil will kill any eggs that have been lying dormant on the tree and prevent them from hatching. This oil can also be purchased from your local garden supplier.
Surround your apple tree with "Butterfly Weed" that has been planted into the ground. The Butterfly Weed contains a type of parasite that will kill the fruit fly. The parasite will not cause harm or damage to your apples. You can purchase the Butterfly Weed from your local plant nursery.