Thistles produce billions of seed that are spread on the wind as well as by birds. If keeping the field mowed does not keep them down then the method of control will need to be looked at. In small areas I mechanically remove them, wearing heavy canvas gloves, in the lawn mowing seems to offer all the control necessary.

What kind of thistles? There are many different kinds, both annuals and perennials. Also, what crop is being grown?

For annual thistles, broadleaf herbicides containing 2,4-D or MCP or Dicamba will generally control them. For perennials, repeat treatments a couple months or seasons apart are usually needed. Glyphosate will take care of them after a few treatments but will also kill everything else. Otherwise, broadleaf products containing dicamba at a high rate will control them for most of the growing season, and agricultural products containing clopyrilid will usually kill them with one treatment with the correct dose without killing grasses. There will be residual the next year to continue control (and eliminate other broadleafed plants), but any new seedlings or escapes should be treated again the following year. All of these products will not harm grasses other than possible temporary burning, but will wipe out broadleafed plants.

And those products will add to the contamination of our envronment.

Although most teenagers unless family will not do it taking a corn knife or other large blade and cutting the plants off under the soil has employed many a young person over the years. My brother got 25 cents a plant until he became old enough to work for an hour.

Depending on your state it may be against the law to give someone under 18 a cutting tool.

Many thistles reproduce by their underground rhizomes, so just pulling alone doesn't work, and rototilling, etc. can sometimes just spread these and around and create more.

We have been battling them in the back of our yard where the gardenn is for years. The biggest groupings are gone, but some still pop up here and there. Get them early.

We spray with round-up, but you'll need to spray over again as new ones appear from under the ground.