The yellowing or whitening of normally green leaves or needles of trees caused by decreased amounts of chlorophyll is known as chlorosis. Viruses, insect damage and other agents or conditions can cause this color change. Iron chlorosis is caused by this element being bound into insoluble forms in alkaline or calcareous soils where the soil pH is > 7. Where the soil pH is 6 or less, iron is most readily available for plant absorption to function as a part of oxidase and respiratory enzymes. Application of chelated iron compounds, such as in Miracid, or adding acidifying substances such as elemental sulfur to the soil, may be beneficial.