Plum Pox Virus: A Threat to Ornamental and Fruit Trees

Plum pox, also known as Sharka, is a devastating viral disease affecting Prunus species, including stone fruits and many ornamental varieties. First identified in Bulgaria in 1915, the virus spread across Europe and eventually reached North America in 1999. Today, it remains a significant concern for growers and regulatory agencies due to its ability to infect a wide range of hosts and its potential to cause severe economic losses.

Symptoms and Diagnosis

Symptoms vary widely depending on the host species, cultivar, age, and environmental conditions. Infected trees may remain asymptomatic for several years, and the virus is not uniformly distributed throughout the plant, making detection challenging. When symptoms appear, they are often diagnostic.

Leaf Symptoms

• Mild light-green discoloration along leaf veins (vein yellowing)
• Chlorotic rings or line patterns

Fruit Symptoms on Peach and Apricot

• Lightly pigmented chlorotic rings or line patterns
• Deformed fruit
• Necrotic areas on fruit (apricot)
• White rings on the stone surface (apricot)

Fruit Symptoms on Plum

• Premature fruit drop in some cultivars
• Darker rings or spots on the skin
• Severe fruit deformation
• Reddish discoloration of the flesh

Host Range

Plum pox virus (PPV) infects a broad range of Prunus species, including plum, peach, nectarine, apricot, almond, cherry, and wild Prunus. European studies have also identified privet (Ligustrum vulgare), walnut (Juglans regia), and euonymus (Euonymus europaea) as susceptible. In North America, the PPV-D strain is the only one detected. Extensive host-range testing has confirmed susceptibility in numerous ornamental and wild Prunus species, while sour cherry (P. cerasus) and 'Snow Fountains' cherry appear resistant.

Transmission and Spread

PPV is a potyvirus transmitted by aphids in a non-persistent manner. Over a dozen aphid species can vector the virus, with the green peach aphid (Myzus persicae) and spirea aphid (Aphis spiraecola) being the most efficient. Transmission occurs during brief test probes, not during prolonged feeding. Long-distance spread is primarily through human movement of infected nursery stock, budwood, rootstocks, or fruit.

Control Strategies

Exclusion

APHIS (USDA) tests imported nursery stock for PPV and other pathogens. Quarantines restrict movement of susceptible plants from infected areas.

Eradication

Infected trees cannot be cured and must be destroyed. Because the virus can persist in roots, sucker shoots from remaining rootstocks must be killed. All Prunus within 500 meters of an infected tree are typically removed. Fruit from infected areas should be disposed of in landfills, not cull piles.

Protection

Insecticides reduce aphid populations but cannot fully prevent transmission because a single probing aphid can inoculate a tree. Barrier crops of non-host species may reduce aphid-mediated spread.

Current Status

In Pennsylvania, PPV has been eradicated. No virus was detected in wild Prunus or weeds. Ongoing surveillance and testing remain critical.

Testing Guidelines

Collect 4-5 cuttings per tree during dormancy or growing season. For growing-season samples, place twigs with leaves in a plastic bag with a dry paper towel—do not add water. Keep samples cool and ship rapidly to a diagnostic lab. Recommended labs include the Pennsylvania Department of Agriculture and Agdia, Inc.