Can invading armies destroy 'open spaces'?

[Arengrey]

I can't seem to locate any rules on how an invading army can destroy an open space like a farm or apiary.

I know there's some information on an invading army occupying a hex for a month and the kingdom's Unrest increases if not dealt with, but I can find nothing on an army burning crops while traveling through enemy territory and it's effect on the economy.

If there aren't any rules, I was thinking about 3 days to fully destroy farms and open spaces in a 12 mile hex.

Thoughts?

[GM_Solspiral]

I'd have it effect movement, based on army size. larger the armty less effect it has on movement

[Hassy]

I'm not using the mass combat RAW, but in my campaign I've ruled that pillaging a hex takes a week, provides the army with some supplies (paying e.g. 1d4 Consumption for a farm hex), and destroys the hex improvement. I might halve the time if you aren't actually taking any supplies, just burning everything.