Despite common advice, I found that simply removing the relevant section from the spawning.xml file didn't turn off feral hordes. I suspect the game uses hardcoded default values if that section is missing.

This version contains my edits that work reliably on my server with Alpha 14.6.


Installation
Find the section in this file that starts with <entityspawner name="NightHorde" dynamic="true" wrapMode="wrap"> and copy that whole section (58 lines). Open spawning.xml in your Data/Config folder, find the same section and paste over it. Done!

Important!
Games in alpha are inherently unstable. Always make backups before you muck about with them!