Common barberry (Berberis vulgaris) is the host for the sexual stages of the stem rust fungus that infects wheat, barley, oat, and rye. The U.S. Department of Agriculture in cooperation with state agencies eradicated common barberry from the north-central states. To accomplish this enormous effort took more than 30 years and many millions of dollars. The effort, however, was well-worth the cost. It saved hundreds of millions of bushels of wheat and other cereals that would have been lost to stem rust. Two factors account for these savings. First, eliminating the barberry bushes took away one source of rust spores to infect the cereals each spring in the north-central states. Second, and more importantly, eliminating barberry broke the sexual cycle of the stem rust fungus. This restricted the development of new stem rust races and made it easier for wheat breeders to maintain effective resistance against the existing stem rust races.
Therefore, it is necessary to identify which barberries can be grown and which must be quarantined from the north-central states. The USDA and state departments of agriculture cooperate to enforce the quarantine. All new barberry varieties proposed for sale must be tested at the Cereal Disease Lab and certified immune to stem rust before they can be registered for interstate shipments.