Pest description and damage The balsam woolly adelgid feeds on the stems of true firs. White or grayish cottonlike masses of eggs or newly hatched purplish-black insects are found on the twigs, branches, or trunk. Heavy adelgid infestations may cover the entire trunk. The feeding insects cause the tree to form swollen, knoblike areas at nodes and tips of infested branches. Adelgid infestations weaken trees, cause foliage to become sparse, and can kill trees. This is a serious pest in the forest and common to the landscape on balsam, grand, subalpine, Pacific silver, and Fraser firs. Balsam fir and subalpine fir are particularly susceptible.
Biology and life history The entire population consists of female insects, which are wingless. They are immobile except for a crawler stage. Crawlers are carried from tree to tree by wind. Eggs are laid on the bark, from which the crawlers emerge. There are two to four generations per year.
Examine adelgid colonies for small lady beetles or their wax-covered black larvae. Syrphid fly larvae also help control adelgid populations. Avoid use of broad-spectrum insecticides that will kill these important predators.
Hand-wipe or use stiff brush to remove minor infestations on smaller trees when possible. Hose infested trees with a strong stream of water to wash off these insects.
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