Green Banners

[zverzver]

Could your trebuche hit your enemy with a sick cow, that would make them ill and reduce morale.

[Empirate]

Exactly, green banners indicate a sickened unit due to cow carcasses launched by Trebuchets.
The cow carcasses stay where they land, and you can see green fumes billowing and wafting about in the vicinity. When a unit gets touched by this cloud, it is sickened, reducing overall fighting effectiveness, and especially morale. When it leaves the cloud, however, these penalties will wear off over time. It's a bit hard to take advantage of sickened enemies without moving your own troops near the carcasses, though, and I've not found a reliable way to use them yet. However, you can create zones that impose hefty penalties for everybody moving through them - which can be an effective method of battlefield control.

[Quillan]

...and I've not found a reliable way to use them yet.

I've had very good success using them in bridge battles and city battles. Defending a bridge crossing, target a unit on the far side of the bridge when it starts to cross. The cows land in the middle of the bridge. They HAVE to run through the noxious cloud, making their morale extremely fragile when they reach your side and the defenders. I've broken Mongol hordes easily this way, but you can't safely pursue them back across the bridge. Do the same thing in a city to defend against attacks or counterattacks down the streets. Just don't advance down those streets yourself until the clouds disperse.

[zstajerski]

yeah diseazed cows rule

[Matty]

Anyone know how long the disease cloud hangs around for?

[FactionHeir]

Quite a long time. Not sure about the exact timing, but IIRC around 10 minutes real time. The effect stays for 10 minutes additionally on the unit.

Actually IMO the cloud does nothing in terms of morale. Found diseased units just as difficult/easy to rout as they would be without, so maybe something isn't working properly.