Why Does My Red Maple Turn Yellow?

Why Deciduous Leaves Turn Yellow

• The color of a maple tree's leaves depends on the season. The green photosynthetic pigment, chlorophyll, is the most abundant in tree leaves and dominates in the spring and summer. As the weather cools, however, photosynthetic food production wanes and the pigments carotene and anthocyanin become the most visible. As fall brings cooler weather and decreasing sunshine, the chemical auxin stops producing, which sets off the growth of the leaves' abscission layer. This specialized layer cuts off water, nutrient and sugar circulation to the leaves which, in turn, triggers the disintegration of chlorophyll. Carotene then becomes more dominant than chlorophyll and produces yellow hues. Even in trees such as the red maple, yellow can be more dominant later in the season when there is less sunlight.

Why Yellow and Not Red?

• Some maples, such as red and Japanese maples, are specifically grown for their vibrant, red fall leaf displays. Unfortunately, some selections of these species turn yellow in the fall or a disappointing yellow-green. In order to avoid this situation, research the cultivars of specific maple species for the reliability of their fall displays. For instance, October Glory red maples reliably turn orange or red in the fall, as does the Columnare.

Nutrient Deficiency

• Maples and birches are more prone than other deciduous species to a nutrient deficiency problem known as chlorosis. Chlorosis is often the result of an iron or maganese shortage in the leaves which, in turn, is often the result of high soil pH. The leaves then turn yellow-green to bright yellow. While in some severe cases leaves turn entirely yellow, the disease is more likely to produce green veins with yellowing in between. Adjusting the soil pH, when possible, is the best treatment, but iron chelate solutions can also be applied for temporary relief.

Verticilium Wilt

• Verticilium wilt is caused by the soil fungus Verticillium alboatrum; maples are among the trees particularly susceptible to the condition. Sometimes a tree will recover, but it's often fatal. Symptoms vary widely, from suddenly wilting and dying tree sections to poor or yellow leaf growth. While leaves can turn yellow in mild, chronic infections or in acute, severe infections, yellowing leaves accompanied by curling, drying, wilting or abnormally red leaves is a cause for immediate concern, as is sudden and abnormal defoliation or sudden die-back.