The most common issues with avocado trees are planting them too deep or with too many amendments that can cause water movement issues. Under watering and overwatering are also common issues. It is a good idea to remove the burm around a avocado tree before the rain comes so the roots don’t stay too wet, this applies in areas where it rains during the winter like Southern California. Avocados really don’t need much pruning, maybe just to control size and to leave room around the bottom of the tree to access irrigation parts easier and to not block the sprinklers. Young avocado trees need plenty of nitrogen so find a organic fertilizer high in nitrogen, you can also use horse manure and chicken manure. Avocados like their soil PH under 7.