dig a small hole.. and see if your water is actually getting to the root zone ... if not.. increase water ....

a long slow trickle will allow water to get to the roots .. where it needs it ....

ken

If the leaves in that area, and the ones falling off look faded it would be spider mites. With a heavy infestation, the leaves eventually fall off. Spider mites love hot dry weather. I don't know how old your burning bush is. A young shrub would be more suseptible to too much or too little water. Since you say that the lower leaves are falling off, it could be over-watering (if it's not spider mites.) Typically a plant not getting enough water will show stress - wilting, leaf drop at the top or outer branches of the shrub. If the leaves seem to turn brown or soft before dropping and are dropping from the lower or lower inside part of the shrub, it could be overwatering.