Why leaves turn yellow?
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. Sucking insects such as aphids, mealybugs and scale remove nutrient laden sap from the plants restricting their ability to make more chlorophyll. Spider mite feeding produces a mottled pattern of yellowing similar to a virus. Many environmental factors cause a plant to yellow. The most basic is a lack of adequate light. When plants become shaded by other plants or by branches higher up on the same plant, the chlorophyll fades away and the leaves yellow. Low light levels in the fall trigger the normal development of fall color. Warm day
