Agriculture Secretary George Greig said Monday the milestone "officially closes the books" on the battle against the virus after three years of monitoring.
The state was declared free of the plum pox virus in October 2009. Testing last summer included more than 41,000 leaf samples, largely from orchards in the region that includes the Carlisle, Gettysburg, York and Lancaster.
The virus can harm fruit-bearing and ornamental varieties of almond, apricot, cherry, nectarine, peach and plum stone fruit trees.
The plum pox virus was found in Adams County peach trees in 1999. Efforts to address it included destruction of nearly 1,700 acres of Pennsylvania orchard trees.