Why do leaves turn yellow?
“Leaves of deciduous plants and needles of evergreens occasionally lose their normal green color. The key reason that plants turn yellow is that they are not able to maintain adequate levels of the green pigment, chlorophyll. When this vital substance is absent, yellow pigments that are also present take over and the leaves or needles fade. Yellowing of plant parts that are normally green is called chlorosis. Affected parts are said to be chlorotic. Diseases, insects and changes in the plant’s environment cause leaves and needles to become chlorotic. Determining which is to blame is not always easy. Fungal diseases such as apple scab or anthracnose in maples, oaks and sycamores cause leaves to yellow. Needlecast diseases on pine, spruce and fir cause a similar effect on needles. Viruses cause the loss of chlorophyll in a mottled pattern on leaves and stems. Sucking insects such as aphids, mealybugs and scale remove nutrient laden sap from the plants restricting their ability to make mo
