Most all commercial growers go to classes, take the exams, and obtain a Pesticide Applicators License that allows them to buy and use products you cannot. So it is not necessarily possible for you to follow there methods, most of which are hazardous to your health anyway.

Trust me the weed is hazardous to my health too. My back is acking and occationally I get so discouraged by the weed.

You can consider using newspaper or cardboard around plants to combat weeds. Also, growers use plastic mulches and you can too. I believe there are chemicals that will kill weeds but not specific, desirable plants. Maybe it is the desirable plant that is genetically engineered not to be killed by Roundup. I am not sure but it would probably not be available to you. Especially in the smaller quantities that you might need. Weeds are one of the biggest problems that farmers deal with. My guess is that the weed free field you saw was covered with plastic mulch. But I could be wrong...

There are a number of different herbicides that are used, which ones depend on the crop you are growing.

They are generally only available as concentrates in quantities for commercial application. One container would last a typical homeowner for many, many, many years which makes purchasing them impractical. Depending on your state regulations and the specific herbicide, you may not need to have a private applicators license to purchase the commercial products.

One of the more common ones is trifluralin, originally sold under the brand name Treflan and now available under a variety of generic names also. It has been available to homeowners under the brand name Preen, although there is another version of Preen made with corn gluten meal that doesn't contain trifluralin.

Trifluralin interferes with seed germination and initial root development in susceptible species. When properly applied, it can do wonders for reducing the amount of weeding you need to do. However, when not applied properly, it can be completely ineffective or wipe most everything out in the treated area.

Because it is applied to the soil, under the wrong conditions or too high a rate, there will be carryover into the next year which can damage susceptible crops, so it is very important to follow the label directions and rates and use them only on the species of garden plants listed on the label, and follow the replanting intervals to susceptible crops.

If you want to find out what herbicides are available, check out state university ag extension web sites for crop production handbooks and search for the crops you are growing. They usually list at least some of the herbicides registered for use in those crops. Then search for the label on those herbicides to quickly find all the other crops the herbicide can be used on to see if they would be a fit for your situation.

Although these products can reduce your weed control workload tremendously, farms will still mechanically weed several times or use labor to keep the fields clean.

Triflualin is probably one of the more toxic General Use Herbicides available. Its toxicity in humans is unknown since no studies have been done that will tell us about that. Acute toxicity in rats and other mammals gas been studied.

Here is a link that might be useful: about Triflualin

Been using/exposed to it for over 40 years, but I'm very careful not to let rats and rabbits swim in it.

Farms use herbicides, plant poisons, so they do not need to mechanically cultivate or use manual labor both of which are costly and cut into the profits expected. There may be some small farms that still use mechanical cultivation, but the large factory farms will not do that.

What weed are you talking about?
What are you trying to grow?
How large is the area you need to manage?