Produce is not going to be under the jurisdiction of the USDA, but rather it will be FDA. You might consider also that it will be subject to the new proposed produce rule of FSMA when that goes into effect. Search instead on the FDA website. FDA uses 21 CFR rather than the 9 CFR of USDA.
Research FSMA and the coming regulations (rule) for produce. You can also reverse engineer the requirements for produce from a GMP audit for produce warehouse and distribution. An audit(current) will encompass both industry standard practice and regulation.
There are rich resources on produce on YouTube e.g. RedLine and other companies that sell software for the produce industry offer amazing webinars that will bring you up to speed. Be aware that control of pathogens will be tantamount to success for the produce items with a history of recall for E. coli, Listeria m, hepatitis.....mushrooms, any kind of sprouts, cantaloupe, tomatoes and in the produce facility in general. Global GAP (good agricultural practice) may be a resource for your quest. Seek out the requirements from the retailers you referenced; the requirements in their audits will surpass what regulation requires.