Crabapple trees (Malus spp.) make attractive small flowering trees for home gardens. However, they do not live forever, nor do they exist without threats of pests, diseases and injuries from wind, lightning or human accidents. Yellowing and falling foliage, die-back of branches and flaking and removal of bark are symptoms of trees that are on the decline. Reduced flowering or strangely-timed leaf-out or blooming can also mark a final effort by a dying tree to produce seeds.
A change in the look or color of crabapple tree leaves is the first sign of a problem. Although yellowing, brown spotting or wilting of leaves is not a direct sign the tree is dying, it does indicate a pest or disease bout that could weaken the tree if not addressed. Leaves may change in appearance and then drop off the tree, often followed by twig and branch death. Once a disease or pest weakens a tree to the point it is no longer making food from its leaves, it is much more likely to die.
Infections by fungi or viruses spread across the crabapple tree from their point of entrance, such as a bark injury. Likewise, boring insects can disrupt the flow of sap in twigs and branches, causing the abortion of leaves, flowers or fruits. Once entire branches lose foliage and bark cracks or flakes away, the situation is serious. Closer examination of the branch may reveal mushroom-like bodies or malodorous oozing gums, a sign the tree is infected and likely destined to die.
Much like the symptoms of dying branches, the trunk is the primary support and means for transport of nutrients, water and sap. Mechanical injuries on the trunk--such as a cut, crack or scar--may allow for pests and diseases to quickly infiltrate the tree. If bark on the trunk is loose, cracked or missing, the health of the wood inside is likely affected and will spread to all parts of the tree, roots included. Fungal crowns or oozing sap or goo from the trunk can also indicate a deteriorating tree.
Crab apples do not live indefinitely. Those of considerable age will slowly decline, usually marked by production of fewer leaves and flowers over the course of the final years. Declining trees are more susceptible to pests and diseases and physical symptoms may be seen in the leaves, branches and trunk.
Dying crabapple trees may flower or leaf-out, either at odd times or repeatedly. This is a natural mechanism common to plants, as it is a last-ditch effort to flower and make seeds before the mother plant dies. It is a means to ensure a future generation of crabapple in the immediate growing area.