I've accidentally damaged one of my apple trees - the tree is about 7 or 8 years old with a trunk diameter of about 3 inches.
It's a tree that has been cultivated to give three types of apple, and when I was moving the (large!) lawn with the tractor mower the long grass box emptying lever caught on the lower branch and tore it off. So that's one type of apple that's been lost.
It has torn off at the point of connection to the trunk.
Will this weaken the tree (I get a lot of wind where I live)? It's not staked.
Should I apply anything to the damaged area?
Hi cider. 
No, you shouldn't apply anything.
Your tree is best healing its own wounds. Depending on the severity of the damage the tree may give up in years to come. (trees tend to die slowly) but apples are very resilient so you could be lucky
It may be worth staking if it is very top heavy now but drive the stake in at an angle from the tree so there is still plenty of movement. This will encourage the tree to root out and brace itself.
Good luck.
No, you shouldn't apply anything.
Your tree is best healing its own wounds. Depending on the severity of the damage the tree may give up in years to come. (trees tend to die slowly) but apples are very resilient so you could be lucky
It may be worth staking if it is very top heavy now but drive the stake in at an angle from the tree so there is still plenty of movement. This will encourage the tree to root out and brace itself.
Good luck.
