Grapevine certification programs are based on the premise that the foundation planting stocks propagated by nursery growers have been tested and shown to be free of pathogens of concern to the industry. Pathogen testing saves growers millions of dollars by providing a good (though not perfect) level of protection from pathogens that shorten the productive life of vineyards and reduce productivity and grape quality.

There are three basic methods of verifying that grapevines are free of harmful viral pathogens: 1) inoculating indicator plants (mostly herbaceous ones) with tissue from the grapevine being tested; 2) a process called “woody indexing,” which involves grafting buds on to a grapevine variety that expresses symptoms; and 3) laboratory testing.