Drying and curling leaves should be cause for concern for any responsible gardener. These two symptoms can frequently be indications or cultural problems such as drought stress or early fall colors, but they can also indicate a plant is suffering from a disease. If you notice dried and curled leaves on a Japanese red maple, for instance, identifying the cause through observing parallel symptoms is the first step to saving your maple tree.
If leaves are dried, wilted and defoliating out of season, cultural management practices could be to blame. If the tree was purchased from a nursery and transplanted in your soil, for instance, its root structures may have been damaged, diminishing their ability to transport water to the leaves. Other causes for leaf wilting and drying include a high water table causing the soil underneath the tree roots to become anaerobic, salty soil because of over-fertilization, soil that's too compacted, or too much mulch placed around the tree. Finally, Japanese red maples do not tolerate direct sunlight exposure, so leaf wilting could result from overexposure to sun. Adjust watering, mulching, shading and other care practices and monitor the tree to see if it returns to normal health.
An infestation of spider mites can cause leaf wilting and drying. Mites feed on leaves with their mouth parts and give leaves a stippled or dotted look. If a fungicide or pesticide was applied to the tree during hot weather, leaves may discolor and wilt. If you see a oily residue called honeydew on the leaves or tiny feeding holes on the green parts of the leaves, the tree is almost certainly infested with spider mites. Treating the spider mite infestation should return the tree to health.
If a Japanese red maple is dug up and replanted, it frequently experiences a short period of "shock" where leaves will dry up and curl due to the time it takes for the tree's roots to establish at the new soil location. The only treatment for this type of shock is to do nothing out of the ordinary. Water the tree according to its regular watering schedule and take care not to overwater as this will only make the problem worse. Water the soil so that it is moist but not soggy and monitor the tree to see if the leaves return to normal color after the maple's roots have grown into the new soil.
Leaf Drop Failure
As fall approaches, Japanese red maple leaves turn brown, wilt and defoliate. Certain specific weather conditions can cause leaves to exhibit this behavior before fall, leading many gardeners to erroneously believe the tree is sick when it is simply anticipating fall weather. The layer of cells found at the base of the leaf stem where it attaches to the tree -- called the abscission layer -- gets dry as fall approaches. Again, unexpected climatic conditions such as a dry but cold winter can cause the abscission layer to fail to release the leaf from the tree after it wilts. If none of the above ailments describe your maple's symptoms, monitor the tree throughout the fall and spring to see if the out-of-season wilting was simply a matter of the tree taking on fall colors early.