Trees may drop a few leaves in the summer and early fall, but the majority of leaf drop on most deciduous trees doesn't tend to occur until after the first frost. There are a few reasons why a tree may drop leaves prematurely, and a proper diagnosis of the cause is necessary in order to treat the condition.
One of the most common causes of summer leaf drop is drought, which causes leaves to turn brown and dry before dropping. Trees have deep roots, but dry and hot weather may mean that they are still unable to seek out enough water. This is especially true if the tree is competing with lawns for water. Watering the tree deeply every week to 10 days during periods of extended dry weather can prevent drought stress.
Leaves that turn yellow and remain pliable after falling off can be the result of over-watering as well. Too much water begins to drown the roots, which leads to yellowing foliage that falls prematurely. Trees growing in clay soils are more prone to over-watering leaf drop, but any over-watered tree can fall victim. Reducing watering, aerating the soil around the roots, and mixing compost in with the soil can reduce issues.
Overcrowding in the crown can lead to damaged branches, which may die back and drop leaves. Sometimes a tree will also drop excess leaves from a crowded crown during hot weather in an attempt to prevent moisture loss through leaf surfaces. Pruning the tree to thin out the crown will prevent this sort of leaf loss. Heavy pruning is best done in late winter, but light pruning can be done in summer.
Some pests can kill tree foliage, causing the leaves to drop. Aphids, for example, are a common pest that will feed on leaves and cover them with a sticky honeydew, both issues that cause leaf death. Caterpillars, scale insects, and bagworms are other common pests that may cause leaf drop. A tree care service can treat the pests so that no more leaves are lost.
Usually, a healthy tree will recover from a fungal problem on its own with a minimum of leaf loss, but sometimes the disease gets the upper hand. Powdery mildew, scab diseases, and blights are common fungal issues to watch for. Your tree professional will determine the specific fungus causing leaf drop so that a care and treatment plan can be implemented.
Contact a tree care service if you are concerned about premature leaf drop.