So how do plagues work?

[GuyOfDoom]

I'm not sure quite what they do either and with the implementing of migration in SE V there is really no reason to target planet population anymore as a 0M planet only lasts about a turn until more people migrate too it.

[Fyron]

Which is great for eliminating the asinine Food Contamination + Cargo Bomb "strategy"...

Presumably, plagued planets should prevent migration to/from the planet, much like they prevent cargo pickup/drop-off.