If the problems are caused by a deficiency, such as an iron deficiency, then yes, you can apply an iron sulpplement to the soil and water it in, or you can spray a cleated iron trace mineral as a foliar spray. Be a little careful of an iron foliar spray to citrus, as it can be a little toxic to the leaves. I myself have nevver had a problem as using iron as a foliar spray, but have heard it is possible. - Millet