Grass Carp can be caught with hook and bait, as common carp.
Here in Japan, there are bunch of people who targets them for fun, we even have grass carp fishing club.
How can they be caught?
Again, not so much differ than common carp.
What would be the bait typically used here in Japan?
GRASS
No, I am not kidding. A guy whom I know from work told me about it as he used this tech a lot. There are many resources about it, unfortunately, they are written in Japanese.
check this web for example, you find how to hook grass on hook.
http://www.daiwaseiko.co.jp/fishing/fish/rever/sogyo1.html
ソウギョ倶楽部
You see some photos on hook/grass system.
Okay, so this is how they catch them here in Japan.
As for my experiences, which is far less quality than those who target the fish here in japan, I would say again, try NOT to think too complicated. Hook and bait, that is all you need....simpler, the better.
The rig is almost the same as common carp. Only difference, IF you want to make difference, is the bait.
You can use juicy fruit as a bait. Pear (especially Asian pear: you can find them occassionally at some grocary store in Lincoln) is one of the best I would say. This bait, actually I learned from Japan, and tried at Salt Creek near Ashland, and caught several grass carp.
Corn is good, but powdering corn with cinnamon powder is even better.
Another bait of my favorite is....BREAD. Cinnammon (sp?) bread is always my favorite bait for me for grass carp as well as common carp.
If the grass caro population is high and veg abundance is relatively low, you may give a shot with grass as bait. If not, you need to attract them, and thos bait which I describe above may do the work for you. Chumming helps as well.
Sam