Ministry of Agriculture
Grape Insect and Mite Pests
Scale Insects
(European Fruit Lecanium Scale, Parthenolecanium corni (Bouché))
(Cottony Maple Scale, Pulvinaria vitis L.)
- Identification
- Life Cycle and Damage
- Monitoring and Spray Thresholds
- Biological Control
- Cultural Control
- Chemical Control
Prepared by D. Thomas Lowery,
Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, Summerland.
Photos courtesy of H. Buchler.
About a dozen species of scale insects are known to attack grapes in various regions of the world, but only two are commonly found on grapes in British Columbia The European fruit lecanium scale (EFLS) and cottony maple scale (CMS) are both soft scales (Homoptera: Coccidae) that rarely cause economic injury to grapes. They are a greater concern in the production of table grapes. The large quantities of honeydew they produce supports the growth of sooty mold fungus that can leave fruit unmarketable. Two species of hard scale (Homoptera: Diaspididae), the oystershell scale, Lepidosaphes ulmi L., and San Jose scale, Quadraspidiotus perniciosus Comstock, can occasionally be found attacking 2 year old wood of weakened vines. Hard scales do not produce large amounts of honeydew and are currently of little importance to the B.C. grape industry.
Identification
Female EFLS, also known as brown apricot scale, when fully grown have a chestnut brown, smooth and slightly shiny protective shell that is around 5 to 8 mm long and slightly longer than wide. Certain races in some regions reportedly produce male scales, but most females reproduce without mating. The small nymphs or crawlers that hatch from the small oval, pearly white eggs are yellow to orange in colour. Mature female CMS are similar in size, shape and colour to EFLS, except that a mass of cottony material containing the eggs, up to 1,000 per sac, extrudes from the rear end. The much smaller winged males produced in late summer have no mouthparts and live for only 1 or 2 days. Males mate with the immature females. Mature scales of both species become brittle after the eggs are laid in mid-summer and can easily be detached from the one to three year old wood with a fingernail. The smaller hard scales (1-2 mm), which are much longer than wide, remain firmly attached to the canes even after death.
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| Adult female cottony maple scale with cottony egg masses being tended by ants. | Immature cottony maple scale |
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| European fruit lecanium scale |
Life Cycle and Damage
EFLS and CMS overwinter as partly grown scales on new canes. Growth resumes in spring and females reach maximum size around early summer when they begin to lay eggs. The newly hatched scale called crawlers hatch and disperse during July and August to the undersides of leaves where they settle and feed until early fall, when they migrate to the current year's wood and develop a hardened protective shell for the winter.
Both species of soft scale feed on the phloem of grapes and a large number of other woody plants, including many fruit trees and ornamentals. Scales are not usually abundant on grapes grown in British Columbia, and direct feeding damage from the removal of plant fluids is rarely a cause for concern. They appear to prefer weak vines, however, and the additional stress might be sufficient to hasten death. Of greater concern, they produce vast amounts of honeydew that can turn grape bunches into sticky, unmarketable messes. Additionally, honeydew supports the growth of sooty mold fungus which further disfigures the fruit.
Monitoring and Spray Thresholds
Because scale infestations often occur on only a single vine or a few vines in a small area, they can be difficult to detect. Partly-grown scales might be observed during pruning, or watch for honeydew on leaves and fruit during spring and early summer. Ants feed on the honeydew and will protect the scale from predators. They can often be seen in large numbers hurriedly running up and down posts or vine trunks to and from infested canes.
To detect when crawlers are active, remove the loose bark in an area near the infestation and encircle the vine with clear tape applied sticky side out or use double sided adhesive. Replace the tape weekly and check for the orange coloured crawlers. A good magnifying glass or dissecting microscope is useful for this purpose
There are no established thresholds for scale infestations. Small numbers of scale on a healthy vine are unlikely to cause damage; treatment is usually only required when the excretion from large infestations fouls table grapes.
Biological Control
Biological control of scale on grapes in British Columbia has not been investigated in any detail, but on other crops and in other regions of the world they are known to be heavily parasitized by several species of wasps and flies. They are preyed upon by lacewings, lady beetles, and other generalist predators. English sparrows and several species of warblers that feed on fully grown soft scale have been known to curtail infestations.
Cultural Control
Healthy vines of moderate vigour are less susceptible to scale infestations and are better able to withstand damage. Routine pruning removes many scales and a small infestation can be pruned out in spring or early summer.
Chemical Control
Movento™ (spirotetramat) is registered for the suppression of lecanium scale. Malathion and insecticidal soap will also help control the active crawler stages in summer. Repeat applications might be required as long as crawlers are active.September 2010
