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Scale Insects
Hemiptera: Many families
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‘Soft’ Scales Armored Scales
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Some Important Armored (Hard)
Scales in Colorado
• Oystershell scale
• Pine needle scale
• Scurfy scale
• Walnut scale
• San Jose scale
• Poplar scale
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Armored Scales Family Diaspididae
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Oystershell Scale
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Oystershell scale can
develop thick colonies
on the bark of
susceptible hosts
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Bark cracking is a
common symptom
of current or
previous oystershell
scale infestation of
aspen
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Oystershell scale infested trees. Note bark cracking.
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Oystershell scale flipped over to exposure lower surface.
Some eggs are visible at right where the ‘test’ has torn.
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Oystershell scale eggs
(left) and recently
hatched eggs,
producing the Instar I
“crawler” stage
Eggs, under the cover
of the mother, are the
overwintering stage.
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The crawler stage usually
occurs in late May and early
June. It lasts for about a
week.
It is the only mobile stage of the
oystershell scale – and all other
armored scales.
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Within about a week the
crawlers have either ‘settled’
or died. They remain in place
where they settled for the
rest of their life.
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Pine Needle Scale
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Mother scale and recently laid eggs. Eggs are the
primary overwintering stage.
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Crawlers usually occur in early to mid May (ca. lilac
full bloom)
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Natural Enemies of Pine Needle Scale
Lady beetles that
specialize in armored
scales (Coccidophilus
spp., Chilochorus spp.)
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Natural Enemies of Pine Needle Scale
Parasitic Wasps
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Poplar Scale on Aspen
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Bark cracking
(right) and bubbling
(below) associated
with poplar scale
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Overwintering stage of poplar scale in Salida,
March 7, 2007
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Lady beetle predators of poplar scale
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Some Important Soft Scales in
Colorado
• European elm scale
• Cottony maple scale
• Striped pine scale
• Pine tortoise scale
• European fruit lecanium
• Soft brown scale
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Soft Scales Families Coccidae, Eriococcidae and others
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Soft Scale Example – Cottony Maple Scale
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Overwintering stage –
Adult females that have
not matured eggs.
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Females swell with
eggs in late spring
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Crawlers move to the leaves in
summer
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Like aphids, soft
scales suck sap from
the phloem and
excrete honeydew.
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Overwintering stage –
Adult females that have
returned to the twigs in
late summer.
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European Elm Scale
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Honeydew is excreted.
Where it lands and
persists, sooty molds
grow.
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Branch ‘flagging’ in late summer can be due to stress
associated with high scale populations.
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Crawlers return to twigs in late summer for overwintering.
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Brown Soft Scale
Coccus hesperidum
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Hemispherical Scale, Saisettia coffae
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Crawler Treatments
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Soft Scales vs. Armored Scales
Soft scales produce
honeydew
Armored scales do not
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Soft Scales vs. Armored Scales
Soft scales typically
produce several hundred
eggs
Armored scales
typically produce a
couple of dozen eggs
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Soft Scales vs. Armored Scales
Soft scales retain mobility
through their lifetime,
moving from foliage to
twigs
Armored scales are only
active during the
crawler period
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Soft Scales vs. Armored Scales
Soft scales typically
produce crawlers for
several weeks in late spring
and early summer
Armored scales typically
produce crawlers for a
week or two in spring
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Principles of Scale Control
• Insecticides timed to coincide with crawlers
• Oils
–Dormant season treatment
–Post-crawler treatment
• Systemic insecticides (limited)
• Hand removal
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Crawler Treatments
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Horticultural Oils
• Primarily act by smothering insects
• Derived from various sources
– Petroleum/Mineral oils
– Vegetable oils (cottonseed, soybean)
– Neem seed extracts
– Fish oils
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Petroleum Derived Horticultural Oils (Mineral oils, paraffinic oils)
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‘Soft’ Scales Armored Scales
Dormant season (dormant oil) applications
of oils tend to work more consistently on
soft scales
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Many current
horticultural oils can
be used on trees
with foliage.
Crawlers and young
settled scales are
targets.
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‘Soft’ Scales Armored Scales
Systemic insecticides applied to the soil
for root uptake are primarily effective
against phloem-feeding soft scales
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Scraping
oystershell
scale
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Principles of Scale Control
• Insecticides timed to coincide with crawlers
• Oils
–Dormant season treatment
–Post-crawler treatment
• Systemic insecticides (limited)
• Hand removal