Answer: Sudden death can be caused by water stress or by salt burn from overfertilization. Tree stakes don't normally release copious amounts of fertilizer, so unless you used too many or placed them too close together, I don't think that's the cause. Dig down near the root system to see just how moist or dry the soil might be. It should be obvious to you if the soil is too wet (which can suffocate roots) or too dry (which can cause drought like symptoms). The tree may perk up once you've resolved the water stress issue. Best wishes with your tree!
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