I'm pretty sure they've scrapped the J-Visa scheme there which has made it harder for oz/kiwis to work in the US.
Many countries in the EU have a special visa for seasonal work so it may be the same in the states.
I would say being an unskilled agricultural worker in the states would be pretty abysmal. you will be working with mostly mexis and other latin american folks and the pay will be shit and the hours long.
Other options are a skilled migrant visa or going in the green card lottery ( a friend of mine got one this way).
Colorado is a big snow sports state so I would look into pathways for working in a ski resort, like I said the many kiwis and ozzies who do snow seasons previously managed to work through the J-Visa scheme. I'm a resident so I never had to worry about visas and such.
This would be a far better environment than pulling turnips in some toxic field.