You can use the pocket factory spell. It targets ground and can be fired in an arc. What you need to do is make the "pocket factory" have a negative hp regen; If you want no delay then set the max hp to 1 and hp regen to -1. Set the pocket factory unit model to an explosion model, say Neutral building explosion.
Now, add the ability - AOE damage upon death to the "pocket factory" unit. Change the spells settings of the AOE damage ability to your preferences. As for the pocket factory spell, set the unit that spawns from the factory to none, or set the interval rate to a high value. As for how long the factory lasts is not an important value, just keep it at 40, it makes no difference.
The Pocket Factory spells works wonders... It is very versatile.