GMO crops often use glyphosate for weed control, which works because the frequently the GMO crops themselves have been engineered to be resistant to glyphosate.
That's not the case with non GMO crops because glyphosate isn't selective - you'd kill your crop along with the weeds if you tried the same approach with non GMO plants.
Hence the use of GMOs is frequently coupled with more intensive use of glyphosate.