As I begin to plant my own crops this week, I know that somewhere in the northern hemisphere this month, a farmer will put a seed in the ground — and the world will have its 4 billionth acre of genetically modified (GM) crops.

Perhaps it will happen in my country of Spain, which is Europe’s leader in GM farming. We can only guess at the location of this milestone achievement, let alone the farmer who will reach it. Yet we know for certain that the great moment will come about halfway through this month.

Truth about Trade and Tech­­nology, a non-profit group based in the United States, has tracked the world’s biotech-crop acreage for years. It posts its findings in the upper right-hand corner of its website...