What about “superweeds”?


In practice, the threat of superweeds is an illusory one. A number of weeds have natural resistance to a range of herbicides, and resistance can also be acquired if the same herbicide is used over a long period of time. In fact, many common weeds already had resistance to a wide range of herbicides before GM crops were introduced. 
There have also been concerns raised about genes conferring herbicide tolerance being passed to wild weed populations by cross-fertilisation. 
However, in many cases, crops are unable to hybridise with weed populations because they have no sexually compatible relatives. If outcrossing were to occur, this would give the weed no competitive advantage outside the field, since it would not be treated with herbicide there. 
GM crops tolerant to broad spectrum herbicides such as glyphosate and glufosinate have become very popular because they enable farmers to control weeds by using occasional spraying at any stage of a crop's development. This makes management much easier, generally reducing the amount of spraying.  Weeds must still be managed through appropriate farming practices.. The growth of acquired resistance to herbicides for GM or non-GM crops can be slowed by appropriate management plans.