The law that started this was enacted around 1995 or 1996.
http://www.ers.usda.gov/publications/aib729/aib729f.pdf
Title V authorizes the Secretary to establish an orderly
process for developing, financing, and carrying out a
program of generic promotion, research, and information
for commodities. Under this new program, interested
parties can petition USDA to establish an industry-
financed promotion program for a commodity
without first obtaining specific authorization from
Congress, as previously required. This title also
requires an independent evaluation of each generic
agricultural promotion program’s effectiveness, including
existing programs, not less than every 5 years.
Title V also provides specific authorization for three
new commodity promotion programs (popcorn, canola
and rapeseed, and kiwifruit).