Blueberries and apples
I bought property with 8 mature blueberry bushes (trees) and 8 apple trees. They had been ignored. I trimmed and fertilized them but they all have mostly stopped producing fruit. The leaves on the apples are full of holes and dropping at the time the fruit usually drops. Can they be saved? Neem oil seemed to make the apple trees worse.
Since they have been left alone for some time they may just need a little TLC to get them back on the right track. The blueberry bushes can be pruned back this winter - January to March. Begin with taking out dead branches and anything that crosses another branch. Cut back 1/3 of height. The next year, do the same until you get them to a manageable height. Any more than 1/3 of plant taken off may cause the plant stress and disease and insects may attack. In March or April add fertilizer around the bushes. Give them water.
Apples trees can be pruned much the same way. Disease and insects are a problem here in the county. Our environment is so conducive to them. You may want to start with a horticulture oil application while trees are still dormant in Feb or March. Then begin with a fruit tree spray afterwards. Fruit tree sprays can be found at any farm supply center, Lowe's, Wal-Mart or where ever you shop. They need to be applied timely throughout the apple season. Follow all label directions. These sprays have a fungicide and insecticide in them to protect against disease and insect issues.
Overall, the answer to your question is the apple trees can be saved (more than likely). Oh and Neem, sometimes is hard on plants when temperatures are high.
Hope this helps.