I can back this up with data I've seen (at the USDA). During the 1990's, GE cotton replaced old standby cotton strains throughout the southeastern United States, some dating back to the early 20th century.  Widely promoted as a means to improve yeilds and reduce production costs, by the late 1990's GE'd cotton strains made up 80%+ of planted varieties, as the two principle companies that produced these seeds slowly acquired or drove out of business the smaller, independent non-GE seed companies.
The GE seeds could not legally be saved, a liscensing fee was assessed on top of the cost of the seed, and the primary advantage of the GE'd strains were that they were resistant to a petrochemical-derived herbacide (weed control) called "Roundup", which just happens to be manufactured by the same company (Monsanto) and/or certain insects.
The Roundup you buy in the hardware store is 1/10th strength of that used on farms.

Turns out that the roundup ready cotton was extremely succeptible to drought, which we here in the southeast have experienced in abundance for 8 of the last 10 years. Average crop yields per acre fell, rather than rising, compared with similar fields (and even test plots) planted with old strain, non-GE cotton. A class-action lawsuit was pending against Monsanto when I left the USDA. I doubt it had meaningful results.