Plum pox (sharka) (Queensland Primary Industries and Fisheries)

Plum pox (sharka)

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Plum pox (sharka)

Have you seen plum pox symptoms?

Be on the lookout for symptoms and report them to Queensland Primary Industries and Fisheries on 13 25 23.

Early detection and reporting of symptoms are the key elements in controlling the pest.

Call QPIF  13 25 23

Plum Pox leaf symptoms
Figures 1 and 2: Leaf symptoms
Leaf symptoms and discolouration of stone
Figure 5: Leaf symptoms and discolouration of the stone
Fruit symptoms of plum pox

Figure 3: Discoloured rings, spots or bands on the skin

Figure 4: External pitting and grooving of the fruit

General information

Plumpox is one of the most serious diseases of stonefruit. It has not been detected in Australia, but could be devastating if it established here. The virus affects all Prunus species, including the cultivated stonefruits plum, peach, nectarine and apricot. It also affects a range of weed hosts such as white clover and nightshade. Plum pox causes high yield losses and has resulted in large areas of tree removal in Europe, where it is well established. In the last two years the disease has been subjected to eradication programs in the USA and Canada.

Overview

What causes plum pox?

It is caused by the plum pox virus (PPV).

What does it look like?

A wide range of symptoms will be seen depending on the susceptibility of the affected variety. Leaf symptoms include diffuse or blurred pale green or occasionally yellow rings, lines or spots. Generally these symptoms are barely seen with the naked eye and will be found at the bottom of a branch, but not the tip. Symptoms on fruit are more obvious, particularly on plum, and include the development of discoloured rings, spots, or bands on the skin (Figure 3). External pitting, grooving (Figure 4), or deformation of the fruit may also occur as well as internal flesh discolouration and marking on the stone (Figure 5).

How does plum pox spread?

Aphids are small sucking insect pests that are capable of spreading the disease over short distances, such as in or between orchards. The green peach aphid, Myzus persicae, which is common in Australia, is one of the more efficient of these plum pox vectors.

Long-distance spread and introduction of plum pox to new regions can occur through the human movement of infected plants or plant parts. The discovery of plum pox virus in several European countries has been associated with introduction of infested nursery stock. The Australian Quarantine and Inspection Service has restrictions on entry of stonefruit plants and plant material to Australia because of this risk.

What are the implications of an outbreak in Australia?

Plum pox can be extremely damaging to fruit production. Tree yields can be severely affected and up to 100% premature fruit drop has been reported in some plum varieties. Infected fruit are unsightly and misshapen and are generally unmarketable. Because of the seriousness of the disease, quarantine restrictions on movement of fruit and plant material would be likely in the event of an outbreak to prevent further spread of the organism. As a control measure, infected trees are normally completely removed from affected orchards in Europe and North America.

Controlling plum pox

Quarantine and certification
Plumpox is extremely difficult to eradicate from a growing district once it becomes established. Because the disease is easily spread on plant material, unaffected areas and districts can be protected through the implementation and enforcement of quarantines on movement of these items. Spread can also be controlled though the use of planting material that is certified free of plum pox.

Tree removal
Infected trees cannot be cured of the disease, and in a newly affected orchard they are normally destroyed as quickly as possible to minimise spread. In France, where plum pox is well established, infected trees are removed within one week of the virus being detected. This method can reduce the incidence of the disease from 10% to 1% percent in an orchard over a three-year period.

Aphid control

Aphid control in stonefruit orchards may have some effect on preventing plum pox spread, but will not completely stop it. While insecticide applications will reduce total aphid populations in orchards, 100% control of this insect cannot be achieved and it may only take one or two aphids to infect a tree.

Resistance

The ability to breed stonefruit cultivars that are resistant to plum pox holds the key to controlling this disease in the future. Some cultivars are known to be more tolerant but as yet none have been identified that are completely resistant to the disease. However, some promising work is occurring in this area in Europe.

Further information

If you would like further information or think that you may have seen plum pox:

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Page maintained by John Nagle
Last updated 16 July 2008



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