Suspicious-looking Farmers

The new owner of Maidge's Farm has recently employed a group of strange farmhands. A string of unusual events have been happening at the farm ever since they arrived.
As you know, the Earth Rune Pillars became very weak recently. We have since discovered it was these farmhands that caused it!
I have thought a great deal about this, but it still confuses me. If they are just ordinary farmhands, how would they have the ability to so affect the rune pillars?! Besides, damaging the pillares would be of no benefit to them...
Well, regardless of who they are, we absolutely forbit anyone from harming the Earth Rune Pillars. Go teach them a lesson. Show them that these is a price to pay for damaging such important artifacts!
:- Winsil Eye of Wisdom Researcher
== On Completion ==
Good! So the power of the Earth Rune Pillars is safe for the time being.
I'm very concerned about who's directing these illegal activities, but right now there are still many other things for me to take care of first. The most urgent is to investigate the real reason behind the rotting and mutating crops, so that the output of the farms can be restored to their previous levels.
:- Winsil Eye of Wisdom Researcher
== Notes ==
While you completing the requirements for this Quest, as you kill the Evil Farmhands and Evil Servants, they will drop a Suspicious Letter which leads to the Suspicious Mail quest.