America is just beginning out to find out the hard way that growing GM crops with no wild relatives to share their genes with doesn't actually mean they'll stay in the field and under control. Even after very few years' cultivation, GM alfalfa is now flourishing on US road verges and spreading its genes far and wide .
Europe has an interestingly different version of the same problem.
Maize, MON 810, is the only GM crop grown in Europe, where it has no wild relatives and doesn't grow easily outside of cultivation. However, no one expected wild weedy relatives of maize to make their way from Mexico and Central America all the way to Europe.
'Teosinte' species were first noticed growing in Spain in 2009 and have now reached such densities that local governments have prohibited maize cultivation in a bid to stop the spread.
The concern is that teosinte can cross-pollinate with maize. It's already an invasive species, and breeding with MON 810 could make it worse.
MON 810 contains a 'Bt' gene which generates an insecticidal protein to keep pests from harming
the crop. Unfortunately, inside teosinte, Bt may well diminish natural environmental control from plant-eating insects.
All the signs are that Monsanto hasn't fulfilled its obligation to monitor the potential environmental hazards arising from its GM maize, and that the European Commission is oblivious to the problem.
As Testbiotech has pointed out:
"If there is now a wild relative of maize in Europe, it is obvious that the risk assessment of MON 810 is no longer valid and that its authorisation for cultivation should be withdrawn immediately by the European Commission."
And, the other maize-growing European countries, France, Portugal and Italy, could also be put at risk of genetic pollution spread using teosinte as a conduit.
Tell the UK and EU governments to face facts: artificial genes are uncontrollable.
 REAL-LIFE GM ALFALFA CONTAMINATION - News, April 2016
Transgenic maize authorisation must be rescinded to prevent crossbreeding with new invasive species, Testbiotech/IFOAM EU Media release, 24.02.16
Photo by Bernardo Bolaños (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons