Trees need periodic deep watering to get them through the dry season.  If they're not being watered deeply with drip irrigation, use a deep-root irrigator (about $30) to get water down to the roots. Attach the irrigator to a hose, insert the stem 6 to 12 inches into the soil beneath the drip line of the tree, and turn the water on gently for 5 to 10 minutes, depending on tree size. Repeat the process at three spots for younger trees, five to seven for large, mature trees.