Large white areas on the leaves may be caused by excess light (sunburn). The leaves may turn yellow or even white if a plant that has been growing in subdued light is suddenly exposed to high light intensities. Another cause of white spots could be mealybugs or cottony cushion scale. Both of these insects have a white cotton-like appearance and are sedentary or move about very slowly if disturbed. The presence of these insects may also cause brown leaves. If populations are large enough, decline and death of leaves can occur. Brown leaves may also be the result of overwatering or overfertilizing. If the leaves are dying from the tips inward, salt injury or drought stress may be the cause.