Care for a diseased sago palm tree by treating it with fungicides or insecticides, depending on the disease. Yellowing leaves on a sago palm can denote a nutritional deficiency, which can be solved with monthly feedings of fertilizer.
Scale insects and mealybugs can infest a sago palm tree, creating white spots and white fuzz on the plant that can eventually kill it. To care for the tree, snip off any limbs that have white spots, and spray the rest of the tree with a neem oil and water mixture or mild alcohol solution several times a day every five days. For more severe infestations, apply a systemic insecticide to the plant.
A sago palm tree is prone to crown rot, a disease that occurs due to fungal infections that thrive in moist or damp conditions. Apply a fungicide to the plant that contains mefenoxam, and prevent further infestations by making sure the soil is well-drained and by not using overhead irrigation. When watering the tree, do not waterlog the soil, as this promotes fungal growth.
If the tree is planted in full sun or in a cold area, the leaves can become scorched or damaged. Immediately remove the damaged leaves, and keep the tree protected from the sun and cold.