IRON DEFICIENCIES - Deficiency of iron can cause interveinal chlorosis or yellowing of the leaves between the veins. This can be common on pin oak and rhododendron. The deficiency can be caused by low iron levels in the soil. Another major cause of iron deficiency is when the pH of the soil is too high. This can reduce the plant's ability to uptake iron even if there is an adequate amount present in the soil. Deficiencies of manganese and magnesium can also cause interveinal chlorosis. A pH test should be done to determine whether the pH is too high or if the nutrient quantity is actually too low. Applications of chelated forms of these elements or reduction of pH can remedy these problems.