Blight

Necromancy
Level: Drd 4, Sor/Wiz 5
Components: V, S, DF
Casting Time: 1 standard action
Range: Touch
Duration: Instantaneous
Saving Throw: Fortitude half; see text
Spell Resistance: Yes

This spell withers a single plant of any size. An affected plant creature takes 1d6 points of damage per level (maximum 15d6) and may attempt a Fortitude saving throw for half damage. A plant that isn’t a creature (such as a tree or shrub) doesn’t receive a save and immediately withers and dies.
This spell has no effect on the soil or surrounding plant life.

Source: Player's Handbook