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Ministry of Agriculture, Food and Rural Affairs

Oystershell scale

Oystershell scale on fruit Oystershell scale
Click to enlarge.

Beginner

Scientific Name
Lepidosaphes ulmi

Identification

  • Eggs are elliptical.
  • Young nymphs are very small, six-legged and white in colour.
  • Males are small winged insects.
  • Females are about 0.7 mm long, cream-white in colour and lack legs and antennae.
  • Feeding weakens the plant and damage can also be found on the fruit.

Often Confused With
N/A

Period of Activity 
Eggs hatch 2-3 weeks after bloom, and crawlers (nymphs) emerge.  Crawlers move around for a while, then settle in to feed. Oystershell scale is present through harvest.

Scouting Notes
Monitoring for scale should be conducted in orchards with a history of damage from this pest. Monitor fruit throughout the season and at harvest for scale. Use black electrical tape (with adhesive side out) around the scaffold limbs of trees, in areas with known infestations, to detect crawler activity. Place bands in trees by mid June for 7-10 days after petal fall and replace every two to three weeks throughout the season. Crawlers yellow bodies will be caught on the tape. Infested trees are weak and foliage is undersized and has yellow speckles.

Thresholds
There are no thresholds for scale insects on apple. In most cases, any fruit injury at harvest warrants corrective measures the following spring.

Advanced

Oystershell scale can affect fruit in most apple-growing provinces and states in eastern North America.

Scientific Name
Lepidosaphes ulmi

Identification
Eggs are elliptical, and young nymphs are very small, six-legged and white in colour. Males are small winged insects. Females are about 0.7 mm long, cream-white in colour, and lack legs and antennae. There is one generation of oystershell scale each season.

Oystershell scale feeding weakens the plant. Damage consists of small, dark brown scales cluster on bark or on fruit.

Often Confused With
N/A

Biology
Scales overwinter as fertilized females with 40-150 egg masses under their scale. Eggs hatch in late spring, approximately two to three weeks after bloom, and young crawlers emerge. Crawlers are small white with six legs, moving to an appropriate site where to begin feeding. After a few hours of feeding, the scale begins to form. Mating occurs and females die shortly after they lay their last eggs.

Period of Activity
Eggs hatch 2-3 weeks after bloom, and crawlers (nymphs) emerge.  Crawlers move around for a while, then settle in to feed. Oystershell scale is present through harvest.

Scouting Notes
Monitoring for scale should be conducted in orchards with a history of damage from this pest. Monitor fruit fruit throughout the season and at harvest for scale. Use black electrical tape (with adhesive side out) around the scaffold limbs of trees, in areas with known infestations, to detect crawler activity. Place bands in trees by mid June for 7-10 days after petal fall and replace every two to three weeks throughout the season. Crawlers yellow bodies will be caught on the tape. Infested trees are weak and foliage is undersized and has yellow speckles.

Thresholds
There are no thresholds for scale insects on apple. In most cases, any fruit injury at harvest warrants corrective measures the following spring.

Management Notes

  • Crawlers spread through orchards by wind, birds’ feet, workers’ clothing and on farm equipment.
  • Carefully examine all nursery trees prior to actual planting. If scale insects are present, discard trees or exchange for clean trees.
  • Plant new orchards away from hardwood stands and from older plantings where scale has been a problem.
  • For established orchards with a history of scale problems, use Superior oil before the tree breaks dormancy when scales have only a thin wax covering.
  • Delaying application until green tissue is present often results in poor scale control, because scales have produced a larger protective wax coating making complete coverage of the insect more difficult.
  • For more information on the timing of products for managing scale, see OMAFRA Publication 360, Guide to Fruit Production - Chapter 3 Apples (PDF) or Apple Calendar only (PDF) :