How do farmers keep their fields free of weeds?

The stuff I grow in my garden, potatoes for instance, gets taken over by weeds if you are not out there everyday hoeing them. Yet you see a farmers field with potatoes growing and there's not a weed in sight. I know they use chemicals, but what chemicals? Can the general public buy these chemicals?

I'm fed up with being organic, it's just not realistic and everything I grow has been attacked by pests. I've got nothing to show for the stuff I've planted. Unless anybody can advise how I can be organic too.
Answers:
Farmers spray with weedkiller and they use tractor-towed implements to dig up the weeds in the furrows but not disturb the spuds.
I'm afraid us lesser mortals who can't use a tractor in our gardens have to use hoes and such like - and pretty regularly too to keep on top of the weeds.
But I think it is worth the effort as food from your garden tastes better. But I don't worry too much about being organic - too many slugs and other pests around for that in my garden.
Don't give up on home grown - and be practical about just how organic it's reasonable for you to be and still get a fair return for your efforts.
Nasty, disgusting, toxic chemicals. yes. There are alot of different ones. I think round-up is one. I would personally try and stick with the organic side. Its partly because of these kinds of chemicals that you have to be cautious before you drink from any natural source of water. About the only safe sources these days are from higher elevations.
It's a little tool called a HOE. You walk the fields & use the hoe to hack down the weed when you see it start to grow (before it goes to seed). You need to import the good insects that can eat your pests & learn how to grow crops that help to alleviate the pest & weed infestation you are talking about. Some farmers plant flowers that help to keep the bugs away!
they use herbicides
Seeds need light to kick off germination.
Dig your weeds in at night when there is no moon.
you can use a selective weedicide the will only kill the weeds in your garden and not the potatos such asDacthal (DCPA), round up would not be a good idea
You answered your own question. You have to tend to them at the very least once a day. Ideally, twice a day and a walkthrough for pest patrol mid day. Farming is not just a hobby and the bigger your field, the more time it will take. For a standard field, an hour total a day will do it.Half Hour in the morning, and a half hour in the evening.
Rent the film "The Future of Food". It will show you exactly why you should avoid any of the modern crops and pesticides. It is as much a political issue as a health issue, although it is just as important as any health issue.

There are a wide variety of options for mantaining an organic or biodynamic crop. It takes a long time to learn. Don't just give up after a couple of poor seasons. You have to develop skills and habits, as well as intuition. It will all happen if you keep your motives pure and remain patient.

This is the skill upon which our very civilization is rooted. It didn't happen overnight for anybody.

You can find local organic farms at your local ogranic grocery. These people are usually very informative and helpful. It's a political issue, after all.
Farmers use lots of chemicals. You can buy a fabric, its usually grey colour and looks like fleece. Cover your garden with it. Make small slits, where you want to plant. The weeds cannot germinate under it.
for a start stay organic spraying chemicals is bad for countryside, from what i learnt in college farmers use field margins around feilds this provides an ecosystem next to the field and helping to remove pests because there is a food chain present. however farmers can apply for a grant from govenmentunder countryside stewardship scheme. if you are in a garden you can not apply for this of course. maybe you could set up a smaller boundary i designated this in my patch and it worked to help the invation of pests. have you also tried interplanting where by you plant two speices of plants together for example Onions and carrots together. as for weeds i tend to just pull them up roots included this stops them groewing straight away.
If you look there are plenty of weeds in the farmers fields. Every field I have ever been in has plenty of weeds, its just that crops are very high and so the weeds which are smaller do not get much light and so die. In the case of the pototoe crop, I think you'll find that the weeds get hoed up when the soil is turned over onto the pototoes.
The herb/pest icides a farmer uses cannot be bought by the general public.

We're a registered farm and use a herbicide to kill perennial weeds. 5mg neat will kill you within minutes,a litre kills weeds over many acres. I think it would be a tad irresponsible if we could all buy this over the counter.

(it could also be argued its irresponsible to spread it over the fields but that another, interesting, question. )

However, these are not used on eating crops, generally they are used on empty pasture. Arable crops do have weeds in them, its just that the crop is so densly planted that it looks weed free.

Organic farms do best with "complementary" planting. eg potatoes intermixed with onions does well
its best not to use chemical if you take a little time to hoe and water your garden will have a great garden its not easily but 1/2 hour a day makes a weed free garden a good way to stop slugs eating small plants is to use chainsaw dust around them also try hanging old CD ups this puts the birds off
Herbicides
Buy any weedkiller that contains glyphosate! bye-bye weeds!
you shouldn;t need weedkillers don't you have to "earth up" potatoes? so that would fit in with the person who suggested a hoe. in the winter don't you have to cover the planting area with old bits of carpet so that the weeds die back. my husbands friend is waiting for the frost to do a lot of the work on his allotment. get a good book from the library or watch a gardening programme on the telly. keep going with the gardening.
Get a sheep or goat or cow. In fact get lots of them if your field is large. Apart from eating the weeds they will also spread a little natural manure for you - free of charge.
er duh it would be sheep cows horses and other farm animals that like eating things like weeds and grass lol
they smoke it.
You are correct farmers use heavy weed killers , i am afraid that vegetable gardening is work and pests are always there , but for every bug there is a solution , IE ladybirds eat greenfly with gusto
certain bugs do not like certain plants . read up on it. putting heavy weedkillers on your ground, remember you and your family are going to consume that food
organic is realistic you just need to know how to do it!!
I would advise you look at John Seymore books. The one I have at home is The Complete guide to self sufficiency. it explains how to combat pests weeks and all sorts of other interesting things.
Using chemicals means that you are eating the chemicals as well. dont forget that.