What is the opposite of organic (food)?

Most often, "conventional" is used as a retronym for "not organic."

It's not great, and a better one may gain acceptance; be patient: these things take time.

For product labels, the USDA uses non-organic to contrast with organic. See these links:

http://blogs.usda.gov/2012/03/22/organic-101-what-the-usda-organic-label-means/

http://www.greenerchoices.org/eco-labels/label.cfm?LabelID=151

As Jeffiekins says in his answer, for the farming method used to produce the food or textile, the terms the USDA and others use are usually organic vs. conventional:

http://www.nal.usda.gov/afsic/nsfc/39.htm

https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-healthy-eating/in-depth/organic-food/art-20043880