Plum Pox

Plum pox is one of the most destructive diseases of stone fruits, and I hope you never see it.

Plum pox in apricot (John Hammond) Public Domain

Also known as sharka disease, plum pox was first observed in Bulgaria in 1915 and now occurs in many parts of Canada, Chile, Europe, India, the Middle East, and North Africa. In Europe, 100 million stone fruit trees are infected with the plum pox virus (PPV), resulting in 80–100% crop losses.
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The disease appeared in a Pennsylvania orchard in 1999, which led the U.S. Department of Agriculture to declare an extraordinary emergency that gave them access to the funds necessary to remove and destroy infected and exposed trees. Plum pox appeared again in 2006 in Michigan and New York. The Department of Agriculture responded quickly and thoroughly. These eradication efforts have cost over $65 million. And the Pennsylvania stone fruit industry may never recover. Plum pox was declared eradicated in the United States (for the time being).

Plum pox symptoms

There are multiple strains of the plum pox virus, but the results are always unfortunate for stone fruit trees.

Symptoms can be very subtle. They can vary by virus strain and host cultivar. Generally, leaf veins turn yellow and light green, or yellow rings may appear on leaves, fruits, and pits. These symptoms may disappear during the heat of summer, only to return in autumn. Leaves may also exhibit crinkling, curling, and puckering. Cultivars with large, showy flowers may become variegated. Fruit may be deformed, turn brown, or develop concentric colored rings. Premature fruit drop may also occur.

Unfortunately, these symptoms do not usually appear until the infection has been present for 2 or 3 years. During this time, several other nearby trees can become infected.

Plum pox transmission

The plum pox virus (PPV) can travel long distances on infected plant material and insects. Grafting infected scions can transfer the infection to healthy trees. Several aphid species can carry this virus.

How to avoid plum pox

Removing infected trees is expensive, and halting the spread of plum pox is the responsibility of everyone growing stone fruits. These tips can help prevent plum pox in your garden (assuming you don’t live where plum pox is already a problem):

• Only buy certified disease-free bare root stock. 
• Quarantine new plants
• Control aphids as well as you can.
• If you suspect plum pox, contact your local County Extension Office or the Department of Agriculture immediately.

Plum pox may not kill fruit trees, but it can reduce production so much that you will probably end up replacing the trees anyway. Infected trees often produce misshapen, acidic fruit.

Efforts are underway to develop resistant cultivars, but those trees are not yet available.