Trees may lose their leaves for a variety of reasons, some of which may be totally harmless, such as seasonal leaf drop in the fall, while others could indicate serious problems, such as pest or disease. Complicating matters even further is that leaf drop may be a symptom of a number of different problems. It is up to the tree owner to determine what that problem may be, perhaps with the help of experts, and find a suitable course of care.
Autumn is the time of the year when many deciduous trees experience leaf drop. Though many may believe it is the temperature that is responsible for trees eventually losing their leaves, that is not the case. In reality, it is the lack of light that triggers the falling of the leaves. Trees do this to conserve moisture during the winter, when it is more likely they will dry out because of not enough water, or at least lack of water in liquid form. Obviously, this type of leaf drop is not only harmless but is beneficial to the deciduous tree. If the leaf or needle drop is happening to evergreens, that may be something to investigate, but some dropping of needles is natural with these trees as well.
Disease and Pests
One of the most common reasons trees lose their leaves at other times of the year is because of fungus. For example, anthracnose is a group of fungi that often attack trees such as maples, oaks, birch, sycamores and dogwoods. Often, the leaves turn an unsightly brown or yellow before falling off. Another common fungus is frogeye leaf spot, which affects some fruit trees, such as apples and pears, with regularity. Anti-fungal sprays can help and in many instances, the infection will last only a year.
Pests also can cause leaf drop. Ash borers, tent caterpillars, locusts and leaf beetles are just a few of the pests that can cause problems. Some species, such as the ash borer, affect only a certain species of tree, while others may not be nearly as discerning.
Problems with Nutrients or Water
Unlike the diseases and pests, which tree owners may be able to do little about, issues regarding nutrients and watering are usually within the owner's control. Too much watering or too little watering can cause a problem, as can too much fertilizer or too little fertilizer. Though the potential causes may be opposites, the symptom of defoliation could be the end result in all cases. Generally, the tree owner will be easily able to diagnose this problem and take corrective action.