Answer: Your red Japanese maple is quite sensitive to hot afternoon sunshine and inconsistent soil moisture. The leaves can curl and show brown edges when the tree is exposed to afternoon sunshine, or if it needs more frequent watering than it has been getting. Curling leaves might also appear if too much fertilizer has been applied.
If the leaves are curled but not crispy around the margins, I'd suspect aphid damage. Inspect the undersides of leaves for colonies of aphids. You can control the population of these pests by hosing them off with a strong stream of water.
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