Sharka: Plum Pox Virus Update -- January 17, 2000

Current Status of Plum Pox Virus
The following contains a summary of the current status of plum pox virus in Pennsylvania. Keep up with the latest information on plum pox virus on the Web at http://sharka.cas.psu.edu.

Initial Identification of Plum Pox Virus in Pennsylvania
A grower in Adams County first recognized the unusual symptoms of plum pox virus (PPV) on Encore peach. After a series of inquiries, a representative from the Pennsylvania Department of Agriculture (PDA) visited the site on September 23, 1999, and collected samples for laboratory analysis. By September 28, 1999, preliminary laboratory results indicated that plum pox virus was potentially the cause of the disease, so samples were sent to the U.S. Department of Agriculture for further testing. On October 12, 1999, USDA positively identified plum pox virus as the cause of the problem and identified it as Strain-D. Strain-D was found in both peach and plum samples.

Survey to Identify Infected Orchards
A survey of all stone fruits within a one-mile radius of the initial Encore peach orchard was begun on October 12, 1999, to determine the extent of the disease distribution. Personnel from PDA and USDA were involved in the survey. Because resting for PPV requires fresh leaves, the time available to test for PPV-infected orchards in fall 1999 was very limited. The collectors walked diagonally across each orchard, collecting leaves from the mid-section of shoots. At the PDA laboratory, eight leaves from each sample were examined visually for symptoms then tested for the virus using laboratory techniques. The laboratory test being used can detect PPV even if there is only one infected leaf in a sample of 10 leaves. On October 20, 1999, the survey was expanded to a two-mile radius from the initial positive orchard block. Additional surveys were conducted in and around Adams County nurseries, in orchards adjacent to the nurseries, and at some other Encore peach orchards. Weeds and wild stone fruit species, which are suspected of harboring the virus, also were tested. A windstorm on November 4, 1999, blew the leaves off the trees, terminating the survey.

Results of the Initial Survey
There were 104 orchard blocks sampled and tested in the Latimore and Huntington Townships in Adams County. Fifty-seven orchard blocks in other parts of Adams County and 33 orchards in other counties were tested. Of the 218 orchard block samples, 200 tested negative for plum pox virus. The 18 infected orchard blocks were all located in the area of Latimore and Huntington Townships. Of these 18 orchard blocks, only 2 showed visual symptoms. In all cases, weeds and wild stone fruit plants sampled were negative for the virus.

PDA placed quarantine on the two Adams County townships on November 6, 1999, which prohibited the movement of budwood or trees from the area. There is no restriction on the sale of fruit from the area since there is no evidence that the virus is spread from the fruit. There are approximately 1,000 acres of stone fruit in the infected area of the two Adams County townships.

Year 2000 Survey
PDA will sample and test all peach orchards in Pennsylvania for PPV at least once. All the orchards in Adams County and surrounding counties will be sampled twice. Door-to-door surveys also will be conducted to identify backyard stone fruit trees that may require testing. 

Eradicating Infected Stone Fruit Orchards in 2000
All 18 stone fruit orchard blocks that tested positive for PPV last fall will be removed. If additional PPV-infected orchards are identified, they will be removed if more than 5 percent of the trees infected with the virus. If fewer than 5 percent of the trees are infected, a USDA risk assessment team will evaluate the situation and make a recommendation about tree removal.

Commercial Orchard and Fruit Tree Nursery Indemnity Program
The Drought, Orchard, and Nursery Indemnity and Flood Relief Act took effect on December 13, 1999. The act establishes the Commercial Orchard and Fruit Tree Nursery Indemnity Program, describes the circumstances under which grants are to be awarded, and appropriates $2,000,000 to fund these grants. The program is intended to provide some financial relief to owners of commercial orchards and commercial tree fruit nurseries who incur costs related to controlling PPV.  

People who wish to apply for a grant under the program may download an application form from the PDA Web site, http://www.pda.state.pa.us. Grant application forms also can be requested by calling (717)-772-5203 or by writing to the Pennsylvania Department of Agriculture, Bureau of Plant Industry, 2301 North Cameron Street, Harrisburg, PA 17110-9408.

Nurseries in Adams County
No nurseries located in Adams County are in the quarantine area. All nurseries and stone fruit orchards next to the nurseries tested negative for PPV when tested by the PDA in 1999. Stone fruit trees budded with wood from the infected area are quarantined and will not be sold by the nurseries. Records indicate that nurseries located in Adams County have sold no stone fruit trees using bud wood from the quarantine area in the last five years. 

Prepared by Fred Gildow, professor of plant pathology, John Halbrendt, associate professor of plant pathology, James Travis, professor of plant pathology, Penn State, and Ruth Welliver, plant pathologist with the Bureau of Plant Industry, Pennsylvania Department of Agriculture.

Penn State College of Agricultural Sciences research, extension, and resident education programs are funded in part by Pennsylvania counties, the Commonwealth of Pennsylvania, and the U.S. Department of Agriculture.

Issued in furtherance of Cooperative Extension Work, Acts of Congress May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture and the Pennsylvania Legislature. T. R. Alter, Director of Cooperative Extension, The Pennsylvania State University.

This publication is available in alternative media on request.

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