Vitality and Durability are drained away from a creature or object of your choice within range. Instantly killing any creature (Other than Undead, Fiends, Celestials, or Aberrations) within range with 21 or fewer remaining hit points. Tthe target rapidly ages before onlooker's eyes, later inspection of the body shows death by natural causes. If it does not kill them, they must succeed on a constitution saving throw or suffer two levels of exhaustion; Plants, Beasts and Constructs make this saving throw with disadvantage, if they are immune to exhaustion, they instead suffer 3d6 necrotic damage if they fail the save. This spell cannot increase exhaustion levels beyond 5.
If you target a nonmagical plant or object that isn't a creature, such as a shrub, weapon, device, or structure; if it is smaller than a cubic meter, it doesn't make a saving throw; it simply withers and decays to rot, rust and dust.
At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, for each spell level above 3rd, the hitpoint threshold by which it will kill a creature increases by 7 and the number of exhaustion levels it inflicts increases by one. If cast at 7th level or higher it can destroy any amount of nonmagical plant or crafted matter within a 15 foot radius, at the caster's discretion.
constructs can not decay why are they weak to this spell