Cultivating corn is definitely one of my favorite jobs. I use a Farmall Cub with mounted cultivators which, in my opinion, is second to none when it comes to single row cultivation. I also plant in 36" rows. The Cub, with mounted cultivators, provides more ground clearance than those 3-point types shown in your photos so you can use it longer into the growing season. Also, the engine is offset, allowing you to look right at the row as your front set of shovels do their work. This lets you to take out weeds closer to the corn, and get on them while the corn is still very small. This is very similar to mowing with a mid-mount compared to a RFM when it comes to how close you can trim to an object. I put in 1-2 acres of sweetcorn each season, usually with 4-5 seperate planting dates, and also from 5-10 acres of fieldcorn. Since they dont make good RR sweetcorn, frequent and close cultivation is critical. The last few seasons I have been putting in RR fieldcorn, and with that I get by with a single cultivation when it is about a foot high. I have one of them 15 gal, 12v, spot-sprayers mounted on the side of my Cub like they sell at TSC for $89. I mounted the nozzle on a bracket that directs the spray onto the row, and I apply it (mixed 3-4 oz per gal) while cultivating. This year, Roundup has dropped in price big-time, so conservation aint such a big deal, but it is still nice to minimize usage. I also apply fertilizer only on the rows with my row-planter so the weeds tend to grow the most there. That Roundup application has more than doubled my fieldcorn yields compared to when I only cultivated a couple of times, and I save more than enough money in fuel, by skipping the second time, to pay for the spray. Amazingly, that single application of Roundup on the rows has cut my cost to produce a bushel of fieldcorn to about a third of what it was prior. There was a time when I hated to spray, but with what fuel costs these days, I am willing to take the risk. If you are going to be cutivating RR fieldcorn and decide to spray the rows, as I suggested, then any of those cultivators you showed would do an adequate job. If you dont want to spray however, I would look for a good, used Farmall Cub or Super A with mounted cultivators which can usually be had for $1k-$2k. One of the things I like best about cultivating is the immediate results when the job is finished. You dont have to wait a couple of weeks to see results like you do with herbicides. With my combo spray/cultivation, I get the best of both worlds - season long weed elimination, and a clean, cultivated field as soon as I am finished. Since they are practically giving away Roundup now (less than or equal to $10/gal), I am also going to walk my sweetcorn with a hand-sprayer instead of a hoe this year. My 10 hp, Farmall Cub is very efficient however so gas would have to get up over $10/gallon for me to ever stop cultivating. That should get me another year or two anyhow.
