Hello, Marie. Too much water that does not drain quickly can create root rot in
trees like this and wilting of the leaves may be a sign of this. Luckily, wilting can be caused by other things such as moisture problems (too little). Since we cannot ask the
tree to tell us if that is what is going on, here are some suggestions:
1. Maintain evenly moist soil. Water only when the soil feels dry; that will help the
tree recover. If wilting persists under these conditions then the
tree may have root rot and it will be up to the
tree to see if it can recover.
2. Avocado
trees need plenty of sun so continue making sure that it gets plenty of it: 6 hours of sun or more.
3. It sure does not need fertilizer when it is stressed like this so, when you fertilize, use Liquid Seaweed or Liquid Fish. It is always a good idea to replace chemicals fertilizers by organic ones when
plants are in stress.
Once it has shown signs of recovery, you can go back to a chemical fertilizer but, I would temporarily switch from a balanced fertilizer to one with a higher level of phosphorus... that is the middle number in your NPK Ratio. Phosphorus is good for roots and blooms; I suggest it here to help the roots recover.
For example, if your current fertilizer's NPK Ratio is 5-5-5 then find one with 5-10-5. You do not have to be exact; something close to 5-10-5 will be fine, like 6-10-4. I would continue using that for two/three applications or so before returning back to the balanced fertilizer that you now use.
Wishing you success,
Luis