Check the moisture level in the soil surrounding your Japanese elm tree. Although Japanese maples can withstand mild droughts, excessive dryness can cause your maple to lose its leaves. Dig a small hole near the base of your tree. Dig down to the root ball and feel the soil. It should feel slightly moist and cool. If it is dry, provide more water.
Give your Japanese maple a thorough soaking until the water reaches the depth of the roots. Depending on your climate and soil conditions, you may need to water to this depth once every week or two, especially during the dry summer months.
Examine the leaves on your Japanese maple tree. Look for small, round, red structures that resemble tiny warts. This is a symptom of bladder galls that signal the presence of a small mite called Vasates quadripedes, a pest that commonly affects maple trees. This pest can cause the leave's to twist and drop from your tree. While winter freezes often kill this pest, insecticides can help remove the mites.
Apply an insecticide labeled for use on gall mites and gall midges, if you discover signs of this type of pest. Apply the insecticide on a calm day when the new leaf buds begin opening. Target the new leaf buds with your insecticide spray, thoroughly and evenly coating the new growth.
Remove the fallen leaves from the ground around your tree. These dropped leaves can rot and form a favorable environment for mildew and pest infestations. Keep the area clean around your tree by clearing up the leaves and branches as they fall.
Feed your Japanese maple tree to ensure adequate levels of nutrients. Apply a time-release, granulated fertilizer in the early spring and early summer. Using the amount recommended on the package instructions, scatter your time-release fertilizer over the surface of the soil beneath your tree's canopy.