There are many factors that may cause a Japanese maple to die. Several pests and diseases are known to affect the plant, creating poor health and eventual death. Japanese beetles, scale, mealybugs and mites usually attack younger trees, while aphids and borers attack trees of any age. Canker, Verticillium wilt and Anthracnose are common diseases that can destroy otherwise healthy trees.
Japanese beetles, scale, mealybugs and mites all leave tiny bumps or cottony dots on the twigs and leaves of the plant. Aphids cause the leaves to wilt, curl and pucker. They suck sap from the plant and may cause deformation of the trunk and branches. Finding clumps of sawdust on the tree indicates the presence of borers. They drill into the bark, girdling the tree and preventing nutrients from reaching the canopy. Mild infestations cause scarring. Regular spraying with strong streams of water and the application of a pesticide may eradicate these pests.
Sap oozing from the bark may indicate the presence of canker, a fungal infection that commonly attacks Japanese maples. Yellowing leaves and discoloration of the sap wood are indicative of Verticillium wilt. Anthracnose causes moist, sunken bruising of the leaves, eventually causing them to rot and fall from the tree. Proper pruning and removal of affected growth may help get rid of these diseases.