Web Master:
Hi JR
Unfortunately, you photo has not come through. If you have a fungal problem you may find the new Black Spot and Fungus Killa - Richgro. This is a systemic fungicide, granules are placed at the base of the plant and taken up by the roots, it lasts longer and is easy to use.
In a hot dry climate take the following points into account. Avocado trees prefer sandy or loamy to allow excess water to drain away. Mulching around the base of the tree helps retain soil moisture. Watering should be deep and infrequent watering is preferred over frequent shallow watering. You can use a drip irrigation system to provide a slow, steady water supply. Although Avocados prefer full sun, saplings do need protection from strong afternoon sun, the plant may benefit from morning sun and protection of the harsh midday and afternoon sun.