According to Garden Guides, armored scales, theilaviopsis trunk rot, Ganoderma butt rot and Phytophthora fungi are common diseases which can affect sago palms. A number of diseases are prevalent to this tree, and most have no cure.
Armored scales cause a serious infestation in sago palm trees. The leaves whither and die during infestation and the trunk of the tree becomes stunted. Eliminating these pests involves three methods: apply horticultural oil, spray chemicals or use natural predators, such as ants.
Theilaviopsis trunk rot is the direct result of the Theilaviopsis fungus. This fungus causes the leaves and the top of the plant to collapse. There is no cure for this disease, so the tree must be removed permanetly.
Ganoderma butt rot is caused by the Ganoderma zonatum fungus. Immediate removal and destruction of the tree is the only option for trees infected with this fungus. This disease thrives in soil, so other trees that are planted in the same location are susceptible to it as well. Choose a different planting location to prevent this disease from infecting newly planted trees.
Phytophthora fungi rots the tree collar, crown, foot and roots. Discoloration of the bark and sap ooze are common symptoms of this disease. Removing and destroying the tree is the only option once the tree is infected. Tear out the tree and roots; then apply a better-draining soil before planting another tree in the same location.