Cycus revoluta "Sago palms," which are not true palms, are related to pine trees. These slow-growing trees are hardier than most other members of their genus. They will survive temperatures as cold as 15 degrees Fahrenheit, according to the University of California Agriculture and Natural Resources Service. Sago palm leaves often show the first visible signs of insect infestation, soil nutrient deficiencies and other problems. Ask your local county extension office for information on soil testing and pesticide use for your area.
Asian Cycad Scale
The Asian cycad scale measures 1/16 inch long and has a white waxy covering. It sucks sap from the undersides of leaves, causing yellow spots on the upper sides of the leaves. A disruption in photosynthesis leads to stunted, browned leaves and leaf death. According to the Texas A&M Cooperative Extension, management should emphasize prevention and biological control. Remove and destroy infested leaves from your plant. Do not purchase plants with signs of infestation on their leaves, and do not plant sago palms close together. To avoid harming the beneficial lady beetle predator, use horticultural oil spray instead of malathion and other broad spectrum pesticides.
Yellow leaves may indicate magnesium or manganese deficiency. If older leaves turn yellow, the sago may need more magnesium. Use a slow-release fertilizer high in potassium and magnesium. A manganese deficiency causes yellow spots or streaks in new leaves. As the deficiency progresses, distorted new leaves turn brown. The University of Florida Extension recommends a foliar application of chelated manganese and a soil application of manganese sulfate. Chelated iron and trace minerals also help to keep leaves green. After new growth appears, you may remove the yellowed older leaves.
In a sunny, hot location, sago palms may develop yellow sunburned leaves. Sago palms tolerate partial shade better than full sun. Leaves will grow larger and have better color in partial shade, according to the University of Georgia Cooperative Extension. Keep seedlings or newly propagated young plants in filtered shade until roots develop.
Sago palms will develop yellow leaves if they receive too much or too little water. Excessive watering can cause root rot, which leads to yellow leaves from nutrient deficiencies. Use well-drained soil and provide enough water to keep the soil moist but not soaked. The University of Georgia Cooperative Extension recommends allowing the soil to almost dry out before watering. Keep seedlings or propagated offsets in moist but not waterlogged soil.