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Wednesday 26 July 2017

Don't panic - winter chills will kill off the green spruce aphid

Aphid damage
Aphid damage

I have been receiving quite a few calls from farmers over the last few weeks who are concerned that spruce trees are suddenly showing brown needles even leading to needle loss.

In most cases, there is no cause for alarm as the culprit is a small insect called the Green spruce aphid (Elatobium abietinum). These aphids are 1 to 1.5 millimetres long, olive to dull green with red eyes and are generally wingless. This little chap is different from other aphids in that it is active during the winter months, usually from October through to March but not during the summer.

These aphids feed on the sap of older needles which develop a pale mottled discolouration during the winter. Black sooty moulds can also develop on some needles. Damage is most noticeable by June as many of these needles fall. New growth is unaffected and the contrast of the old sparse needles and the green new needles is striking.

Control of these aphids is limited: chemicals are more likely to kill you rather than the aphids. There are natural enemies like ladybirds but they can only provide limited control. Fortunately, trees seldom die, but increment can be somewhat reduced. Cold winters keep the aphid populations down; a period of cold temperatures will kill off the aphids.


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