Forestry advice: Spruce trees are showing all the signs of damage from green aphids
It probably sounds a bit strange to say this now but I'm all for a really cold extended spell in the winter - it is a great way to control some pests and diseases. Take aphids for instance. The green spruce aphid is a very good case in point.
Over the last couple of weeks, I've noticed that spruce needles are gradually taking on a mottled appearance and are turning a blotchy pale yellow colour.
That is when I know that farmers will soon be ringing me concerned that their spruce trees have suddenly died. They notice the needles turning brown and then drop off.
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 (allegedly - I haven't looked them in the eye yet) and are generally wingless. This little chap is different from other aphids in that it is very active during (mild) 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 later in spring / early summer as many of these needles fall. New growth is unaffected and the contrast of the old sparse needles and the green new needles is very 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.