Linoleum knife. I used to use the wooden handle ones but now buy the plastic handle knife with the serrated edge. Every farm vehicle I own has some in them. After you cut the twine, wrap it around the handle and you can get a good pull on it if needed. Plus they are good for cutting air seeder hose in the spring and digging up seed in the ground.Back in the day we used twine and a one of them yellow handled curved blade carpet knives (we called it a banana knife) always worked great for us, and less chance of it going through a tire if you lost it (skinny blade) we use net wrap now, although only for our horses... (40 bales a year) I made a single bale pipe feeder and I drop the bale on end outside the feeder grab the end and walk around a couple times, ball the wrap up and throw in in the tractor, scoop the bale up with the forks underneath and dump it in the top of the feeder... works fine for me.
Canadian Tire will have them on sale for 5 bucks.