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| EASTERN
SPRUCE GALL ADELGID Adelges abietis (Linnaeus) |
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The eastern
spruce gall adelgid is a key pest of Norway spruce, Picea abies,
in northeastern United States. Occasionally, it also infests white spruce,
P. glauca, red spruce, P. rubens, and Colorado blue spruce,
P. pungens. In Pennsylvania it is a pest of plants in landscapes,
nurseries, and Christmas tree plantations. In the past, literature referred
to this species as an aphid.
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| Life History | |
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This pest
overwinters on spruce as female nymphs in bark crevices on the current
year's twigs, especially at the bases of buds. In the spring they
resume feeding and mature into adults. Females usually start laying
eggs about the time buds start to open. Each female lays between 100-200
eggs that normally are laid in small groups. Young nymphs hatch from
eggs in 7-10 days and crawl into the bud and among the bud scales.
Once in the bud, they begin feeding on the new tissue. Feeding stimulates
most plant cells to produce an individual gall where each needle should
develop. The result is a series of affected needles, which collectively
grow into a stunted pineapple-shaped gall. This species becomes enclosed
in spaces between the swollen round needles. They remain there until
the galls are fully developed, begin to turn brown, and open from
late July through October. During this period of time mature winged
individuals fly from galls to lay eggs on host needles. Eggs hatch
into young nymphs that overwinter. One generation occurs each year
in Pennsylvania.
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Fig. 1. Eastern spruce gall adelgid damage. |
| Description | |
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The galls
formed by this pest are short, pineapple-shaped growths (Fig. 1).
They are usually less than 25 mm long, green at first, but turn brown
when they open and the adults emerge. Eggs are covered with white
waxy filaments.
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| Damage | |
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Feeding by
this species stimulates the formation of a gall at the base of current
year's growth. Infested trees are seldom killed, but the aesthetics
of an infested tree may be greatly reduced.
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| Management | |
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Nonchemical
Pruning and destroying green-colored galls during June or July before they open, and therefore, before adults emerge, is practical for light infestations on a few small trees. Chemical Apply horticultural oil according to label directions as a dormant treatment, before new growth starts, when temperatures remain above freezing. Horticultural oil removes the glaucous bloom (blue color) from both Colorado blue spruce and Koster spruce. To manage overwintering life stages of this pest, apply registered insecticides according to label directions from mid-September through early October. A second alternative is to treat infested plants in April prior to budbreak, before females mature and start laying eggs. For optimal results be
sure to thoroughly cover the bases of buds. Also, the use of certain
insecticides may cause outbreaks of spruce spider mite, mainly because
of their effect on mite predators. Be sure to monitor for outbreaks
of spruce spider mite when using treatment materials that may impact
mite predators. |
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| Warning | |
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Authored by: Gregory A. Hoover, Sr. Extension Associate November 2001 ©
The Pennsylvania State University 2001
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