[Chris Byler]

Originally posted by Taqwus:
suddenly surrounded by fatigue-causing undead plant beings.

You might also try the point blank damage spells (Burning Hands etc.) - make sure the caster and any friendlies near him are resistant. Abysian Salamanders hit the whole square, as do Fire/Ice Drakes and the Harvest Blade (not necessarily the most practical solution, but effective). Some other attack spells, mostly Fire, hit the whole square. Fire elementals and Fire Shield could fry all the dragonflies.

If they do all turn into manikins after you kill them once - then you'll have to kill them again. All of the above will work (except maybe the ice drake - are manikins cold immune like real undead?), plus I think manikins can be Banished.