Deer can be big problems for farmers, which is why they often have permission to hunt on their farms during most times of the year. However, for the average home gardeners who have vegetable gardens or even a couple of apple trees, they, too, can have deer problems. While hunting may not a viable option for you (nor legal), there are fortunately other techniques you can try, which can be quite effective in protecting your apple trees from deer.
Scatter deer repellent around your trees. There are several things you can use, including a commercial deer repellent that uses blood meal and clumps of human hair. You can even use cut up bars of hand soap. As deer become accustomed to one scent, switch it to another.
Scare away the deer. A fake dog, a scarecrow and even hanging pots and pans that bang in the wind can scare away the deer. You can also purchase a motion sensor alarm that goes off when the deer come to close to your apple trees. A radio too will sometimes work. Use a scare technique along with the scent repellent for better results. Continue to change things around as--or before--the deer become used to your tricks. For example, start with the fake dog and some deer repellent and then in a couple weeks, try the radio with the hair.
Rope off or net around your apple trees. The most inexpensive way to do this is to install fence posts. For mild to moderate deer problems, 2 to 4 foot posts should suffice. Between the posts, attach monofilament twine (e.g., fishing wire) every 6 inches. You can also use deer netting.
Fence off your apple trees for a long-term solution to severe deer problems. For the average home gardeners, a privacy fence that is 8 feet tall may be a good solution. The deer can see in and even if they can smell the apples, they can't jump 8 feet and probably wouldn't try since they cannot be sure it is safe on the other side. You can also use a 6-foot fence (not a privacy fence), but install it pointed outward at a 45-degree angle. You can even use a smaller fence, such as one that is 4 foot high, but use 8-foot posts. At the top 4 feet, use the monofilament twine as described in step 3.