Spruce gall is caused by adelgids, insects that are close relatives of aphids and that make similar gall formations on pine, Douglas fir and larch in our region. The spruce gall adelgid spends part of the year on an alternate host such as any pine, Douglas fir or larch. On these trees, the adelgids look like snow or white fluff on the bark.
On spruce trees, spruce gall adelgids form the characteristic cone-like galls. Adelgids are invulnerable to any other control measure besides hand collecting when they are in the gall stage. Sprays at different times of the year, particularly in early spring and later in August and September, seem to be most effective. Seldom will adelgids cause severe damage or kill the kinds of trees that we can grow here, although the damage they do cause can be objectionable.
The cooley spruce gall adelgid has a very complex life cycle which is not fully understood. Adelgids are a small group of insects that are closely related to aphids. The normal life cycle of this adelgid consists of six different forms of the insect over a two-year period on two hosts: spruce and Douglas fir. In Saskatchewan and Manitoba where there is no native Douglas fir, the adelgid has the capability of completing its life cycle entirely on spruce. Only the first form of adelgid causes a formation of galls, whereas the remaining forms feed openly on needles. Another form of the cooley spruce gall adelgids produce white, cottony protective covers for their eggs. These cottony covers appear as white specks early in the spring and continue throughout the summer, and can cover an entire tree during a severe infestation.
Damage first occurs in late May when the new growth of the branch tips form into cone-shaped galls. Galls vary in length from 25 to 75 mm and 12 to 18 mm in diameter. The galls are green at first but later turn a reddish-purple colour. The old galls dry out and turn a reddish-brown colour, and may remain on the branches for several years. During a heavy infestation, young spruce may be severely deformed because the buds die on the gall-infested twigs. On established spruce, the growth and vigor may be reduced, but trees are rarely killed.
Some control may be achieved by picking the new galls off as they form and burning them. This will improve the tree's appearance and reduce the aphid population. Chemical control of the cooley spruce gall adelgid can be achieved by applying carbaryl or malathion in early spring just as the buds begin to open. Contact us today.