Viral Diseases | WSU Tree Fruit | Washington State University Skip to main content Skip to navigation

Viral Diseases

Viruses Affecting Apple

Generally, apple viruses are transmitted through grafting. Tomato ringspot virus is an exception, and it causes apple union necrosis and decline.  When trees are healthy, and they have virus-free rootstock, the tree will usually remain healthy. Infected trees in the orchard can spread viruses slowly to adjacent trees through natural root grafts (reference). Here is a list of the most common viruses affecting apple. Note that some of these may also affect other crops and will be noted in the descriptions. A list of major viral diseases affecting pear are listed after the apple section.

Apple Mosaic Virus

  • Causative agent: Apple Mosaic Virus
  • Vector: Spreads by vegetative propagation, it is not thought to spread by insects or pollen. It may spread by root grafting.
  • Crops affected: Apples, Pear, Plum, Peach
  • Disease description: Pale or yellowish banding areas along the leaf veins occur on the leaves of many cultivars, in the spring. The chlorotic spots may become necrotic later in season from sun and heat, and leaves may fall early. All apple varieties are susceptible, but ‘Golden Delicious’, ‘Jonathan’ and ‘Granny Smith’ are very susceptible. Related to Prunus necrotic ring spot virus (PNRSV). Fruit may be small or deformed. Loss of crop can occur, depending on cultivar. Pears are symptomless.
  • Management: Transmitted through budding and grafting with infected trees. Use certified virus tested and virus-free planting material to propagate trees. Affected trees and roots must be removed and destroyed.
  • Resources:
    • Apple Mosaic Virus, Pacific Northwest Plant Disease Management Handbook, webpage. (Accessed: 1/17/17).
    • Apple Mosaic Virus, E. V. Podleckis, et. al., eXtension webpage, 2011.  (Accessed: 1/17/17).
    • Apple Mosaic, University of California IPM webpage. (Accessed: 1/17/17).

Apple Union Necrosis and Decline (AUND)

  • Causative agent: Tomato ringspot virus (TmRSV),
  • Vector: spread by Dagger nematodes, Xiphinema americanum (sensu lato).
  • Crops affected: Apple, Peach, Nectarine, Prune
  • Disease description: Grafted trees with fruiting varieties resistant to TmRSV and rootstocks tolerant to this virus have a problem with this disease (e.g., ‘Delicious’/MM.106). A tolerant rootstock can harbor the disease but not suffer from it. When infected trees are at bearing age, budbreak may be delayed, leaves might be small and sparse, and pale green. Shoot growth is reduced. Separation of graft union can occur in severe infections. Tree death may occur. Under bark near union there is a distinct necrotic line. The graft is spongy and orange colored. With strong winds, it is possible for the top of the tree to break at the graft union. The virus is present in broadleaf weeds in orchards (e.g. dandelions) and spread to trees through nematodes. Hosts to this virus include fruit and ornamental trees, vegetables and weeds. AUND is caused by incompatible graft unions involving a resistant scion grafted onto a susceptible but tolerant rootstock.
  • Management: Use virus-free and nematode resistant rootstock. Grow trees in sites with no history of the disease and preferably that were preplant fumigated to control nematodes. Use broadleaf herbicides to control weeds.
  • Resources:

Latent Viruses in Apple

Latent viruses live in their host plant without causing symptoms. When a virus-infected scion is grafted onto susceptible rootstock, the virus is transmitted. (Three common latent viruses in apple include: Apple chlorotic leaf spot virus (ACLSV), Apple stem pitting virus (ASPV), and Apple stem grooving virus (ASGV). They can occur individually or together, and can cause diseases in other fruit crops. They are not as much a problem in commercial apple production.

Apple Chlorotic Leaf Spot (ACLSV)

  • Causative agent: Apple chlorotic leaf spot virus (ACLSV)
  • Vector: none known; graft transmissible.
  • Crops affected:  Apple, Crabapple, Pear.
  • Disease description: Many crabapple cultivars are affected with apple chlorotic leaf spot. Some new cold tolerant and fire blight resistant rootstocks are hypersensitive to one or more latent viruses.  This virus causes pear ring pattern mosaic, and has been found in all pome and stone fruit species.  Leaf symptoms include: chlorotic spots, distortion and stunting.
  • Management: Use only virus-free certified planting material.
  • Resources:

Apple Stem Pitting Virus (ASPV)

  • Causative Agent: Apple stem pitting virus (ASPV)
  • Vector: none known; graft transmissible.
  • Crops affected: Apple, Crabapple, Pear.
  • Disease description: When a susceptible rootstock (e.g., new cold tolerant and fire blight resistant rootstocks) has an infected scion grafted to it, hypersensitive reactions can occur including a downward curving of leaves and pitting and weakening of the rootstock.
  • Management: Use only virus-free certified planting material.
  • Resources:

Apple Stem Grooving Virus (ASGV)

  • Causative Agent: Apple stem grooving virus (ASGV)
  • Vector: none known; graft transmissible.
  • Crops affected: Apple, Crabapple.
  • Disease description: Rootstocks of M. sylvestris ‘Virginia Crab’ can develop Apple Decline and a brown necrotic line at the graft when infected; complete breakage of the tree can occur at the graft union. Scion tissue above the graft union may swell. Some new cold tolerant and fire blight resistant rootstocks are hypersensitive to one or more latent viruses.
  • Management: Use only virus-free certified planting material.
  • Resources:

Apple Green Crinkle Disease

  • Causative agent: Trees with green crinkle disease are infected with Apple Stem Pitting Virus (ASPV), Apple Stem Grooving Virus (ASGV), and Apple Chlorotic Leaf Spot Virus (ACLSV), but it is not known which are responsible for the disease.
  • Vector: unknown
  • Crops affected:  Apple.
  • Disease description:  Fruit develop depressions that become more severe as the fruit matures. Distorted fruit may appear on one or two limbs. There are no leaf symptoms.
  • Management: Use only virus-tested planting material that is free of all known viruses.
  • Resource:

Flat Apple Virus

  • Causative agent:  Cherry Rasp Leaf Virus (CRLV).
  • Vector: Dagger nematodes, Xiphinema americanum; Can also spread through contaminated budwood during propagation.
  • Crops affected:  Apple, Cherry
  • Disease description:  Apple fruits become flattened from both the stem and calyx sides of fruit. Leaf rolling up from the midrib may occur in infected varieties (e.g., ‘Red Delicious’).  Disease is spread from tree to tree by nematodes in the soil. This virus can move between cherry and apple plantings. Apple trees planted on sites that previously had cherry trees affected with CRLV will become infected. Many orchard weeds serve as a host. Flat apple symptoms are more severe on ‘Red Delicious’ and related cultivars.
  • Management: The use of virus-tested, virus-free planting material; Remove infected trees as soon as symptoms appear. Fumigation for replant sites may delay disease development; control the nematode vector.
  • Resource:
    • Flat Apple Disease, Pacific Northwest Plant Disease Management Handbook, webpage.  (Accessed: 1/17/17).

Russet Ring Virus

This virus occurs in ‘Golden Delicious’ and ‘Newtown’ apples. Symptoms are rings of russeted areas on the skin of the fruit. Develops more in cool growing seasons. Can only control by using virus-free nursery stock. See the Market Diseases of Apples, Pears and Quinces, C. Pierson et. al. and the Pacific Northwest Plant Disease Management Handbook for more information about this virus disease.

Star Crack Virus

The ‘Golden Delicious’ and ‘Gravenstein’ varieties in the Pacific Northwest are susceptible. Affected fruit are distorted, and cracks may develop anywhere. Cork-like tissue forms on surface of fruit on healed cracks.  Must use virus free bud and nursery stock to control this disease.  See the Market Diseases of Apples, Pears and Quinces, C. Pierson et. al. and the Pacific Northwest Plant Disease Management Handbook for more information about this virus disease.

Viruses Affecting Pear

Pear Stony Pit Virus

  • Causative agent:  unknown
  • Vector: None known
  • Crops affected:  Pears. The Bosc pear variety is highly susceptible to this virus.  It can also be found in d’Anjou and Forelle.  Bartlett is a symptomless carrier.
  • Disease description:  The pits appear to be cone-shaped. Numerous pits can develop in the fruit, giving it a distorted appearance. Cells at the base of the pits develop hard, stone-like masses. Transmitted by budding, grafting, and root cuttings. Associated with Apple Stem Pitting Virus (ASPV).
  • Management: Use virus-free planting material, remove infected trees
  • Resources:

Pear Stem Pitting Virus

  • Causative Agent: Apple Stem Pitting Virus (ASPV)
  • Vector: graft transmissible
  • Crops affected: Pears
  • Disease description: The Apple stem pitting virus causes infection in some pear cultivars, even though symptoms are not seen. There are longitudinal grooves on the xylem under the bark near the lower stem when tree is infected. Ridges form on the inner bark also.
  • Management: Use virus-free planting material
  • Resource:

Pear Red Mottle Disease

  • Causative Agent: Apple Stem Pitting Virus (ASPV; or very closely related)
  • Vector: none known, graft transmissible
  • Crops affected: Pears
  • Disease description: Symptoms are easy to see in late summer and fall. Dark red spots near finer leaf veins appear.
  • Management: Use scions and rootstocks that are virus-free
  • Resource:

Pear Vein Yellows Virus

  • Causative Agent: Apple Stem Pitting Virus (ASPV; or very closely related)
  • Vector: not known
  • Crops affected: Pears
  • Disease description: Smaller secondary leaf veins are yellow in color.  Along veins there may also be flecking, red mottling and necrotic spots; it has been reported that symptoms are more pronounced when the weather is cool.  Trees that are infected may have reduced vigor compared to healthy trees.
  • Management: Use scions and rootstocks tested and virus-free.
  • Resource:

Pear Necrotic Spot

  • Causative Agent: Apple Stem Pitting Virus (ASPV; strain of the same filamentous virus)
  • Vector:  not known, graft transmissible
  • Crops affected: Pears
  • Disease description: Circular chlorotic spots 2-3 mm in diameter on leaves in early summer. Spots will turn deep red or black. Trees may shed leaves prematurely and have a decreased yield. Fruit show no symptoms for most cultivars.
  • Management: Use only virus-free certified planting material
  • Resource:

Apple Stem Grooving Virus (ASGV) and Apple Chlorotic Leaf Spot Virus (ACLSV)

These are both major viruses affecting pear. The summary descriptions are listed above under Latent Apple Viruses. Additional information can be found in this research article:

Effect of thermotherapy on elimination of apple stem grooving virus and apple chlorotic leaf spot virus for In-vitro-cultured pear shoot tips, L. Wang, et. al., HortScience, 41(3):729-732. 2006.

Viruses Affecting Cherry

Little Cherry Disease

Western X Disease

  • Causative Agent: Candidatus Phytoplasma pruni
  • Vector: Leafhoppers (Colladonus geminatus); also transmitted by budding or grafting
  • Crops affected: Cherry
  • Disease description: Fruit are small and pointed, and pale in color. Fruit has a bitter taste. Affected fruit is often in one area of the tree, while the rest of the tree has normal fruit.  Trees on Mazzard rootstock can show symptoms for years and not die; trees on Mahaleb rootstock are quite susceptible, and usually die within a few years or less. Between the scion and rootstock, a dark line may occur under the bark with pits and grooves.
  • Management: Spray trees to kill vectors, then remove trees. If many trees are infected, removing them may not be economically advisable, as healthy looking fruit can still be produced. Manage nearby ornamental hosts including choke cherry and bitter cherry. Treat orchard for leafhopper, and weeds that harbor leafhoppers.
  • Resources

Cherry Leaf Roll Virus: (Cherry Decline)

  • Causative Agent: Cherry leaf roll nepovirus
  • Vector: spread by use of infected budwood, and root grafting; may be transmitted by pollen also.
  • Crops affected: Cherry
  • Disease description: Flowering is delayed. Leaf margins may roll upward, as if wilted. Leaves in some cultivars may turn a purple-red color early in the season, and light green spots may appear in others. Fruit is small, and ripens late.  Shoot dieback can occur.  Tree decline occurs more quickly if trees are simultaneously infected with Prune Dwarf Virus (PDV) and Prunus Necrotic Ringspot Virus (PNRSV).
  • Management: Remove infected trees.  Apply herbicide to the freshly cut stump of removed trees.  Use only virus tested and virus free planting material.
  • Resources:

Cherry Mottle Leaf Virus

  • Causative Agent: Cherry Mottle Leaf Virus
  • Vector: Microscopic scale mite (Eriophyes inaequalis); spread by budding or grafting.
  • Crops affected: Cherry, especially Bing and Napoleon (Royal Ann); Van, Rainier, and Lambert are symptomless carriers.
  • Disease description: Trees on the edge of orchard are usually infected first.  Leaves on affected trees may be distorted, puckered, with irregular mottling that is light green to yellow in color.  Fruit set of infected trees is reduced and fruits may lack flavor besides ripening late and being small.  Terminal shoot growth is stunted.
  • Management: Use virus free planting material. Remove infected trees to prevent spread of the virus. Destroy wild cherry trees near commercial orchards.
  • Resources

Cherry Twisted Leaf

  • Causative Agent: Cherry twisted leaf virus
  • Vector: Spread by budding and grafting; no known vectors
  • Crops affected: Cherry.  Bing and Rainier are susceptible cultivars.
  • Disease description: Leaves twist downward and to the side, and remain small. Tissue sections on the underside of midrib and veins on leaf die.  Older trees of medium vigor tend to show greater symptom severity.
  • Management: Use virus free planting material. Remove infected trees when symptoms appear. Choke cherry stands near commercial orchards should be removed.
  • Resources:

 Cherry Rasp Leaf Virus

  • Causative Agent: Cherry rasp leaf virus
  • Vector: spread by dagger nematodes (Xiphenema americanum); grafting; dandelion and red raspberry are host plants for the virus.
  • Crops affected: Cherry
  • Disease description: The spread of disease in a tree or orchard is usually slow, and causes flat apple on apple trees. Lumps or growths form on the underside of leaves between veins. Leaves may fold and distort, and surface texture becomes rough.  Fruit production is reduced in infected trees.  Young trees and branches that are severely affected will die.
  • Management: Use virus free planting material. Remove infected trees. Pre-plant fumigation for nematodes.
  • Resources:

Necrotic Rusty Mottle

  • Causative Agent:  Necrotic rusty mottle virus
  • Vector: Spreads through infected bud wood; vector is unknown
  • Crops affected: Cherry, all cultivars are susceptible
  • Disease description:  More severe symptoms may occur in cool springs.  Spots and areas of dead tissue appear on leaves around 3-6 weeks after bloom. Severely decayed leaves will drop. Buds at the ends of shoots do not open or swell and will die. Bark of infected trees may have shallow areas of decay with associated wound gumming.  Infected trees may die in as few as two years.
  • Management: Remove infected trees; Use virus-free planting material. Some pollinizing cultivars are symptomless hosts.
  • Resources:

 Prunus Necrotic Ringspot

  • Causative Agent: Prunus necrotic ringspot virus (PNRSV)
  • Vector:  Spreads by infected pollen; transmitted by budding and grafting
  • Crops affected:  Most Prunus species including sweet cherry, sour cherry, peach, almond, rose, etc.
  • Disease description:  Leaf and bloom development may be delayed in the spring for infected trees.  Leaf symptoms usually consist of a few rings or chlorotic areas that can develop into necrotic spots and a shot-hole or tattered appearance later.  The disease is associated with reduced fruit growth, yield, and delayed fruit maturity.  Large areas of bark on the tree may die and produce wound gumming.  Susceptibility of infected trees to winter injury is increased.
  • Management:  Use virus free planting material.
  • Resource:

Cherry Rugose Mosaic

  • Causative Agent: Prunus necrotic ringspot virus
  • Vector: Grafting, seeds, and pollen from infected trees spread this disease.
  • Crops affected: Cherry
  • Disease description: Turned up leaf tips and delayed fruit maturity (up to 7-10 days) occur with this virus. Leaf symptoms include brown necrotic spots which drop out, giving leaves a shot-holed appearance.
  • Management: Remove infected leaves before bloom. Use virus-free planting material and scion wood.
  • Resources:

 Rusty Mottle

  • Causative Agent: Rusty mottle virus
  • Vector: Spread by infected budwood.  No known vector.
  • Crops affected: Cherry
  • Disease description: Older leaves turn a mottled yellow, symptoms appear first in lower center of tree. Two-three weeks before harvest rusty yellow leaves drop, removing 30-70% of tree’s leaves.  Infected trees will have reduced vigor and some main limbs may die back.
  • Management: Remove diseased trees when found. Plant virus-free trees.
  • Resources

 Prune Dwarf Virus

  • Causative Agent: Prune dwarf virus
  • Vector: Spread by budding, grafting, seeds and pollen
  • Crops affected: Sweet cherry and Sour cherry
  • Disease description: Sweet cherry leaves may be mottled, show yellow rings, have shot-holes, or have no symptoms.  They may be longer and narrower than usual.  In trees 25 years old or older, there may be more blind wood in infected trees.
  • Management: Use virus-free trees; Rogue out and replant young, infected trees
  • Resources
Viruses Affecting Stone Fruit

Peach Mosaic Virus

  • Causative Agent: Peach Mosaic Virus
  • Vector: unknown
  • Crops affected: peach
  • Disease description: Leaves develop chlorotic patterns in the early season. Spots become necrotic and fall out leaving a shot-hole appearance. Fruit will show symptoms of a rough and bumpy surface. Fruit size is reduced.
  • Management: Use virus tested, virus-free planting material
  • Resource:

Prune Dwarf Virus

  • Causative Agent: Prune dwarf virus (PDV)
  • Vector:  Spread by infected pollen; Transmitted by budding and grafting and by seed
  • Crops affected: Sweet Cherry, Sour Cherry, Italian prune
  • Disease description: Leaves on sweet cherry trees are longer and narrower with the virus. Symptoms may only show on one branch or section of an infected tree.  Leaves may show chlorosis, necrosis, leaf distortion and stunting.
  • Management:  Use virus tested and virus free bud wood and rootstocks.
  • Resource:
    • Prune dwarf virus, Pacific Northwest Plant Disease Management Handbook, webpage. (Accessed: 1/17/17).

Prunus Stem Pitting (also called prune brownline and constriction disease)

  • Causative Agent: Tomato ringspot virus
  • Vector:  Dagger nematodes (Xiphinema spp.) transmit the disease from weeds to trees, seeds (e.g. dandelion) can spread the virus over long distances. Spread through grafting and budding of infected plant tissue.
  • Crops affected: All stone fruit species, and it is found in broadleaf weeds such as dandelion
  • Disease description: Leaves cup upward along middle, turn shades of yellow to red, and fall from tree early. Symptoms result from girdling of the trunk.  Tissue at the graft union may die and tree breakage can occur under high winds.  Trees that are infected may produce many small fruit, which will ripen early and drop.  Affected trees may die within two years of leaf symptom expression.
  • Management: Use virus tested, certified virus free trees. If nematodes are found, fumigation can be considered. Control broadleaf weeds.
  • Resources:

Plum Pox Virus (Sharka)

  • Causative Agent: Plum pox polyvirus (PPV)
  • Vector: transmitted by aphids; can be spread through infected bud and nursery stock.  Virus can spread by root grafting.
  • Crops affected: All Prunus species including apricot, plum, peach, latent in cherry trees.
  • Disease description: Serious virus of stone fruit with potential to devastate production. On plum, pale green spots and rings or lines appear on the leaves; Rings and spots can occur on the fruit, as well as sunken lesions. Peach leaf symptoms appear as chlorotic bands along veins, and twisting. Rings and spots appear on peach fruit. Various common weeds are hosts (e.g. white clover).  Fruit from infected trees lack flavor, may mature early and often drop prematurely.   Tree roguing should include roots.
  • Management: Use propagative material that has been tested and is known to be virus free.
  • Resources:
Additional Virus Resources

WSU Resources

 

Virus Research Reports

 

Extension Resources

 

Trade Articles About Viral Diseases

 

Technical Articles About Select Viral Diseases

 

Washington State University