How do you catch a grass carp in a farm pond?

Bow and arrow.

If there is much grass it's just short of impossible to actually get them to bite. If you are just trying to remove them I'd go the bowfishing route or snag them with a large treble hook. If you're really set on catching them a flyrod is about the best way I know of. I've done pretty well with flies that look like cotton seeds, moss balls, or mulberries. Wait until they are feeding on the surface and then try to make a quiet cast well in front of them and move the fly as little as possible. I've heard of people catching them on grape tomatoes, nightcrawlers, corn, and I've caught one on a grasshopper. Be ready for a long wait, they are not an easy fish to catch on rod and reel.

corn for sure! everything loves corn, i catch them on corn all the time.

I know a buddy who catches them on plums. one day he set a plum out and got a phone call. Wasn't paying attention and when he turned back around his whole rod and reel were gone!

Jeff

There isn't too much grass but they look pretty big.

I fish a pond that has vegetation along the shore and the carp go in the vegetation in the middle of summer. I take a hook and ill it with sweet corn. I place a bobber at about whatever depth keeps the corn at mid depth (6 feet of water, bobber at 3 feet etc) I throw the bobber and corn to just outside the weed edge. It gets bit most of the time. My wie goes bass fishing with me and when she gets bored i do this for her. Not many freshwater fish that will fight like a 10lb plus carp. I have caught a few on a fly rod when the cottonwood trees are shedding. They are a runaway train on a fly rod.

Fly rod for sure. Nymph or suspending bug imitator. Ive used a fly from Umpqua called the San Pedro Crab that is made of green dubbing. It is very small and suspends when using a furled leader. I dont think much of their fight though. Big weight, slow runs, they seem to loose their energy quick and go belly up waiting to be pulled in.