I will recommend some organic methods since I am not too familiar with chemicals you can spray on the apple tree. Depending on the amount of tree that is infected, you can try one ore more of the following:

1. Spray the affected areas with high pressure water. That may get them away from the apple plant and go elsewhere.

2. Get some lady bugs and they are pretty good at attacking the aphids, if you can manage to keep them around for an extended period of time.

Aphids typically attack plants that are over fertilized (with a lot of nitrogen) or you have experienced extended wet cool weather. You can't do much about the latter but for the former, you can back off on over fertilization, if that is an issue.

I will recommend some organic methods since I am not too familiar with chemicals you can spray on the apple tree. Depending on the amount of tree that is infected, you can try one ore more of the following:

1. Spray the affected areas with high pressure water. That may get them away from the apple plant and go elsewhere.

2. Get some lady bugs and they are pretty good at attacking the aphids, if you can manage to keep them around for an extended period of time.

Aphids typically attack plants that are over fertilized (with a lot of nitrogen) or you have experienced extended wet cool weather. You can't do much about the latter but for the former, you can back off on over fertilization, if that is an issue.

Here is a helpful video regarding Aphids

https://www.youtube.com/watch?v=8UI_Bm0aTl0&list=PL3VEy0_tuFgSA596wd13Ka2UfA3Pw0S1s&index=1