There are many signs that a tree is diseased or dying, and if you suspect that’s the case, you should call an arborist immediately. You might notice rot or fungus on the trunk or that the tree is beginning to lean to one side. Brittle branches or signs of root damage are other indicators that a tree is in trouble. If the tree is dying, it might be time to cut the tree down so it doesn’t fall.

If the roots are still alive, the dead tree will usually try to put out new shoots. That doesn’t mean the tree will survive or that the dead parts of a tree will come back to life. If parts of the tree have died and turned gray or rotten, nothing will bring them back to life and they need to be safely removed.

Generally, you should prune around 20% of an apple tree’s growth—and never more than 30%. This means that if you have a severely overgrown tree, it can take a few seasons to prune it back enough to produce the healthiest fruit. 

If you’re dealing with a newly planted or juvenile tree, hold off on pruning beyond the initial shaping. Wait at least a couple of seasons into fruit production since pruning can increase the number of water sprouts and unproductive foliage.

In most cases, you should not use a pruning seal on trees after trimming. Applying a sealant can interfere with the tree's natural healing process, and it does not guarantee protection from pathogens. Instead of sealing the cut, the best practice is to support the tree's natural recovery by providing it with plenty of water and a dormant-style fertilizer. However, there are exceptions. Pruning seals may be recommended for very vulnerable species, like elm trees, in areas where dangerous diseases such as Dutch elm disease are prevalent. In these specific situations, the protection offered by a sealant can outweigh its downsides. For advice tailored to your situation, especially after cutting large branches, it is best to consult a local tree trimming professional.