Iowa and most other states have a real weed problem. Canada thistle, quack grass, horse nettle and field bindweed (creeping jennie) have spread rapidly in the last 10 years in Iowa, and other new but equally serious weeds have become established.
Porter, R. H.
"Weeds Are on the Spot,"
Farm Science Reporter: Vol. 1
, Article 5.
Available at: http://lib.dr.iastate.edu/farmsciencereporter/vol1/iss2/5