Insect of the Month - Scale Insects

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

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