Need to kind of and how old are your apple trees? Also, what kind of yield have they been giving for the past several years, same, up or down? Need to know at least that for an answer that you can apply. If this is a general question then the general answer would be, maybe yes and maybe no, depending on........

We've never fedd any fruit tree or shrub just watered as needed!

We also need to know approximately where you are from, David--not exactly, nearest city is fine. We feed our apple trees here in Phoenix, AZ, but this is harsh country for apples!

I give the fruit trees a balanced fertiliser every couple of years.....slow release is good