| Peach -- Plum Pox (Sharka) |
| Cause:
Plum pox virus (PPV) of which there are several strains. The disease was found in North America for the first time in 1999 in Pennsylvania and has now been detected in New York and Michigan as well as Ontario and Nova Scotia, Canada. Surveys for the virus in 2000 and 2006 did not find the virus in the Pacific Northwest nursery industry or Oregon’s cherry orchards. Known strains include D, which is the one found in North America, M (most severe), C (cherry), and Ea (El Amar). Globally, PPV is the most economically important virus of stone fruits.
PPV infects all Prunus fruit tree species, almond and many ornamental trees. In Europe, wild Prunus species are reservoirs of the virus. Herbaceous hosts include an array of common weeds, such as white clover and nightshades. The virus can survive in the roots of rogued infected trees and can also spread by natural root grafting. The suckers produced from the remaining roots of rogued infected trees carry the virus and therefore must be removed if control is to be achieved. PPV is transmitted by aphids in a non-persistent manner, and is retained by the aphid for no more than a few hours. Aphids appear to spread the virus, not to immediately adjacent trees, but to trees several spaces away. Systemic spread of the virus within a tree may take several years, and in the meantime the virus may be distributed very irregularly. Seed transmission in Prunus is known not to occur with the D strain, but there are some reports of seed transmission with the M strain. Long distance spread is through distribution of infected budwood and nursery stock. Experimental transmission from infected fruit to hosts has been shown and could be a possible mechanism for long distance spread. |
| Symptoms: Many trees do not show symptoms for up to four years following initial infection. Severe symptoms can be observed on many cultivars of apricot, plum, and peach trees. However, the type and severity of symptom development depends on the particular cultivar. Sweet and sour cherries have recently been confirmed to be natural hosts. Symptoms may appear on leaves or fruits of infected trees, and are particularly evident on leaves in spring when chlorotic spots, bands or rings, vein clearing and even leaf deformation is evident. Infected fruits show chlorotic spots or rings, and diseased plums and apricots are deformed with internal browning of the flesh and pale rings or spots on the stones. Much of the affected fruit drops prematurely, 20-30 days before the normal maturity date, and fruit that does remain on the tree lacks flavor and is low in sugar content. Symptoms, however, are highly variable. |
Cultural
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References: Plum pox virus (Sharka) Resources. West Virginia University. |
| Content edited by: Jay W. Pscheidt on January 1, 2009 |
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