| | Diaspididae family (armored scales) or Coccidae family (soft scales); there are other scale families
Crops Affected: wide range of plants, including trees, shrubs and perennial plants, both deciduous and coniferous
Life Cycle:
- Small sucking insects, which may also inject toxins during feeding
- The majority of stages and types of scales are small, oval to circular in shape, flattened, lack wings and a separate heads or any easily recognizable body part
- Most scales that are seen are female
- Adult males are rarely observed; differ in appearance from females – size, shape, wings, antennae
- Not all species have males
- Life stages include adults, eggs, and typically at least 2 nymphal instars/growth stages
- Mature adult females produce 50-200 eggs that may be hidden under their bodies or secreted externally under a protective cottony or waxy cover
- Eggs hatch (within 1-3 weeks) into the first nymphal stage, referred to as Crawlers, as they are mobile
- Crawlers are typically yellow to orange in colour
- Crawlers walk over the plant, are moved on the wind or transported by carriers (people, birds, etc.)
- Settle down and begin feeding within a couple of days
- Settled nymphs do not typically move for the rest of their life cycle as they mature
- Some species will move slightly or will move later in the season
- Scales tend to be 1/8 to ¼ of an inch in diameter
- Scales can be found on lower leaf surfaces, stems, branches, bark, etc.
Soft Scales (e.g. brown soft scale, European fruit lecanium, etc.)
- Considered tropical and would be more of a concern in a greenhouse
- Secrete honeydew, generally
- Typically overwinter as second stage nymphs
- May have tiny legs and antennae (all barely visible) and may move very very slowly after settling
- Typically ¼ inch in diameter
- Don’t produce a protective shield that can be separated from the insect body
Armored scales (e.g. San Jose scale, oystershell scale, etc.)
- Have a hard, waxy shield
- Shield may have a slight bulge/bump/lump/knob and visible concentric rings
- Perhaps more of an issue in interior plantings (cooler than greenhouses)
- Do not generally secrete honeydew
- Typically overwinter as adult females and first stage nymphs – this is only the case in mild regions or protected areas
- Most stages lack obvious appendages and spend their entire lives in one location
- Crawler stages and adult males may have appendages and move somewhat
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San Jose scale | Brown soft scale |
Photo: United States National Collection of Scale Insects Photographs , USDA Agricultural Research Service, Bugwood.org | Photo: Lesley Ingram, Bugwood.org |
Symptoms:
- In situations with a very abundant population of scales, some plants may appear weakened and slow growing
- Plants may appear stressed, with yellowed leaves ad premature leaf drop
- Some plant dieback may occur
- Dead leaves may stay on dead branches
- Sticky honeydew can be observed, as well as association visible symptoms, such as black sooty mould and the presence of colonies of ants
Monitoring:
- Check plants for scales or their symptoms (honeydew, sooty mold, ants)
- The use of tape traps or other methods can be used to determine populations and presence of crawlers in spring
- Confirm type of scale and whether scales are actually alive prior to considering controls
Management:
- Typically not required for most plants that are healthy – even with heavy populations of scale, plants may not be unduly affected
- Ensure plants are healthy and have sufficient moisture, fertilizer, etc.
- Physically remove (and destroy) infestations; wash off crawlers and honeydew
- Natural predators and controls can keep populations in check; introduced predators and parasites can be effective biological controls
- Chemical controls must be applied at the correct time (prior to scales settling) and/or must be systemic
- Horticultural oils applied in the dormant season can be effective
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