Weeds are one of the most serious problems faced by the American farmer. Losses due to weeds are estimated at 3 billion dollars annually in the United States.
The best way to control weeds is to stop them before they reach the farm. This is true of both noxious weeds and the so-called common weeds which are too frequently taken for granted. It is much easier and cheaper to prevent these pests from establishing themselves than to eradicate them. The seeds of a few kinds of weeds can be carried long distances by natural means. For instance, dandelion seeds are wind-transported; cockleburs and stickweeds are carried by animals.
But the seeds of most weeds are spread by man, most commonly planted with crop seed. A good example is the spectacular spread of giant foxtail. Ten years ago this weed was rare in Iowa. Now it is one of the major late summer grassy pests throughout much of the southern half of the state. Giant foxtail has been a successful hitchhiker, mostly with weed-polluted legume seed. It is still on the move, county to county, farm to farm.
Isely, Duane and Bragonier, W. H.
"Seeds of Iowa noxious and common weeds,"
Bulletin P: Vol. 7
, Article 1.
Available at: http://lib.dr.iastate.edu/bulletinp/vol7/iss131/1