It is normal for the lower leaves of most varieties of azaleas to turn solid yellow at this time. Varieties that are semi-deciduous will have the most yellow leaves. Azaleas that are under drought stress and those growing in excessive sun will often have more yellow leaves. You can reduce the amount of leaf loss by watering deeply during dry spells and by applying 5-4-7 Acid Blend fertilizer in April, early June and late August. Be sure to bring in samples of yellowing leaves for us to look at because nutritional disorders, mites, lace bugs, diseases or other problems may be responsible for the yellowing.