There is a spell in the Spell Compendium called, no joke, Junglerazer. Dru 3, Sor/Wiz 3.
Deals 1d10 per caster level (max of 10d10) points of negative energy damage to vermin, fey, animals, plants and plant creatures in the area. The area is a 120' line.
Seems right up your alley.