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Ministry of Agriculture, Food and Rural Affairs

San Jose Scale

Female scale (Alan Eaton, University of New Hampshire Coop. Extension) San Jose scale on limb (Alan Eaton, University of New Hampshire Coop. Extension) San Jose scale on fruit San Jose scale San Jose scale
Click to enlarge.

Beginner

Scientific Name
Quadraspidiotus perniciosus

Identification

  • Females give birth to live young (crawlers), and do not lay eggs.

Crawlers

  • Small (0.2 mm),
  • Orange-yellow in colour,
  • Oval-shaped,
  • Six legs,
  • One pair of antennae.

Adults
Females:

  • Nearly round and located beneath a waxy scale covering (about 1.6 mm in diameter) with a raised nipple in the centre of the covering.
  • Remain under their scale coverings their entire lives.

Males:

  • Small winged insects about 1 mm in length,
  • Golden brown in colour,
  • Emerge in flights from beneath elongate scale covers once they have matured,
  • Flight usually occurs during apple bloom, with a series of three overlapping summer flights from mid summer through fall.

Damage

  • Scale is found on limbs or fruit.
  • Confirm San Jose scale injury by cutting away bark to reveal a reddish discolouration.
  • Feeding on fruit is most abundant around the blossom and stem ends of fruit, often resulting in small gray patches on apples, surrounded by a small red discolouration around the area.
  • Early season severe infestations may result in small, deformed fruit.
  • Heavy scale infestations can cause a decline in tree vigor, growth and productivity. 
  • Infestations can kill twigs, limbs and eventually the tree.

Often Confused With

  • Forbes scale- Forbes scale looks similar, but has a raised red area in the center of the scale. 
  • European fruit scale- European fruit scale is also similar but is lighter in colour than San Jose scale.

Period of Activity
San Jose Scale becomes a nuisance during petal fall, and continues to be a pest until harvest. 

Scouting Notes
Monitoring for San Jose scale should be done in orchards with a history of damage from this pest. It is rarely distributed uniformly throughout a tree, and may only infest a few trees in the block. Monitor for scale during pruning or on fruit at harvest. 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.

Thresholds
There are no thresholds for scale insects on apple. In most cases, any fruit injury at harvest warrants corrective measures the following spring. If scale-infested fruit are found after the first generation of crawlers have settled, measures against the second generation are recommended.

Advanced

San Jose scale is the most common scale seen in orchards, and recently became more of a problem, perhaps due to reduced spray programs. Host plants of San Jose scale include apple, pear, quince, plum, apricot, sweet cherries, currants, gooseberries and numerous woody ornamentals.

Scientific Name
Quadraspidiotus perniciosus

Identification
Females give birth to living young (crawlers), and do not lay eggs. Crawlers are small (0.2 mm), orange-yellow in colour and oval shaped.  They have six legs and one pair of antennae.

Adult females are nearly round and located beneath a waxy scale covering (about 1.6 mm in diameter) with a raised nipple in the centre of the covering. They remain under their scale coverings their entire lives.

Adult males are small winged insects about 1 mm in length, and golden brown in colour.  Males emerge in flights from beneath elongate scale covers once they have matured. Male flight usually occurs during apple bloom, with a series of three overlapping summer flights from mid summer through fall.

Scale is found on limbs or fruit. Confirm San Jose scale injury by cutting away bark to reveal a reddish discolouration. Heavy infestations of scale insects – particularly on young trees – seriously reduce tree vigour, growth and productivity. Severe infestations can kill whole limbs.

San Jose scale feeding on fruit is most abundant around the blossom and stem ends of fruit, often resulting in small gray patches on apples, surrounded by a small red inflamed area. Early season severe infestations may result in small, deformed fruit.

Often Confused With

  • Forbes scale- Forbes scale looks similar, but has a raised red area in the center of the scale. 
  • European fruit scale- European fruit scale is also similar but is lighter in colour than San Jose scale.

Biology
San Jose scale overwinters on the tree as immature scales. They remain dormant on the bark until tree sap starts moving in the spring, and are full grown by late May. Active males emerge from their scales and seek females for mating. Females are immobile and remain under scales throughout their lives. After mating, females begin to produce living young, usually at the rate of 9-10 per day. They reproduce for six weeks and bear from 150-500 offspring (crawlers). Crawlers move to find a suitable place to develop (bark or fruit), and then insert their mouthpart through the bark and begin to feed on sap. Three weeks later they molt and shed their skin. Scales are attached to bark by their sucking mouthparts. As the insects continue to grow, they build a waxy shell around them that protects from dessication, predators and pesticides. Females develop through two nymphal instars to the adult, while males develop through four instars. Scale populations increase rapidly in hot dry weather, and females produce more than 300 million offspring each year.  There are two full generations each year.

Period of Activity
San Jose Scale becomes a nuisance during petal fall, and continues to be a pest until harvest.

Scouting Notes
Monitoring for San Jose scale should be done in orchards with a history of damage from this pest. Monitor fruit 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.

Thresholds
There are no thresholds for scale insects on apple. In most cases, any fruit injury at harvest warrants corrective measures the following spring. If scale-infested fruit are found after the first generation of crawlers have settled, measures against the second generation are recommended.

Management Notes

    • Crawlers spread through orchards by wind, birds’ feet, workers’ clothing and on farm equipment.
    • Successful scale insect control starts with prevention.
    • 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) :