Mr J of Leicestershire, sent pictures of his Colorado spruce tree (Picea pungens), bought as a specimen in November 2006, which started suffering foliage damage in late summer in 2007 and again in late summer 2008, gradually affecting much of the tree.
Newly-planted semi-mature trees often suffer severely after planting, because their roots cannot explore the surrounding soil fast enough to get sufficient water to sustain the foliage in summer. This is why it is important to water newly-planted trees. However, damage from lack of water shows up as loss of foliage, needles in this case, to the parts furthest from the roots, such as the tips of branches and the top of the tree. In both 2007 and 2008 the summers were especially wet and so damage from lack of water was less likely than in dry years.
In this case the damage does not affect the tips, but older foliage. Older foliage can lose needles if it is shaded within the tree, but here, unshaded needles are also being lost.
The supplier of the tree suggested that conifer red spider mite was the cause. Our insect experts (entomologists) did not think the damage was consistent with conifer red spider mite. The finely mottled foliage typical of conifer red spider mite appears absent. On the other hand, green spruce aphid is a common pest of spruce trees and this tree shows damage typical of this pest; stems devoid of older foliage, but with current growth in good condition.
Green spruce aphid infests trees in winter and spring, but the damage often only becomes apparent in spring when the needles begin to drop. As the aphid could be active now, we advised Mr J to monitor the tree and use a suitable insecticide to control any re-infestation. We suggested that he shake branches over a sheet of paper and examine the paper for skins. Aphids cast their skins as they grow and these white skins (like a ghostly aphid) can sometimes be seen after the aphids have moved on.
Mr J was not sure that this explanation fully fitted his observations, as the damage he saw appeared in later summer. However, he is keeping watch for the aphids and is reassured that the damage should be covered as the undamaged tips grow, as long as further green spruce aphid damage does not occur.