Known overseas as “sharka” (Slavic for “pox”), plum pox is not harmful to humans when eaten, but the incurable disease will eventually cause discolored fruit and massive drops in crop yields. Viral symptoms may look like a nutritional deficiency or insect injury. As the disease progresses, ring-like lesions can appear on fruit. Eventually, the tree almost stops producing fruit altogether, causing crop losses of 80 to 100 percent.

Adams County grower Jim Lerew (left) discusses plum pox with Adams County extension agent Tom Garretson.

Within days of discovering the virus, both the state and federal departments of agriculture recommended a quarantine of four grower operations in Adams County, including the Lerew Brothers Orchard. “This is as serious a disease invasion as we have ever seen.” says Ruth Welliver, plant virologist for the Pennsylvania Department of Agriculture.

In March of this year, Lerew, after receiving destruction orders from federal and state agencies, had crews bulldoze 150 acres of fruit trees—every peach and nectarine tree in his orchard—and burn them. Jim Lott, who owns Bonnie Brae Fruit Farm in Gardners, had to destroy 227 acres of peach and nectarine trees, a tract containing 25,000 trees that last year produced about 40,000 bushels of fruit worth roughly $400,000. Two other growers also received destruction orders. “Financial losses are higher than a year of lost production,” Lerew explains. “It takes six years for a new fruit tree to start producing in volume and it costs a lot to remove and replace the tree itself. If the virus has spread beyond our area, it probably means we won’t be able to compete with other states.”

By July, scientists had found no infection of fruit trees beyond the quarantined area in Pennsylvania. However, the Canadian Food Inspection Agency reported the discovery of plum pox virus in nectarine trees in an orchard outside Niagara-on-the-Lake, Ontario. Canada has implemented a plum pox virus testing program to determine the extent of the disease and measures to control its spread.