Adelgids

Overview 

Relatives of aphids, these insect pests can damage the tender growth of trees by sucking out the plant's juices. Adelgids only feed on conifers, including true firs (Abies spp.), Hemlock, Larch, Pine, and Spruce. Some notable species include Balsam Woolly Adelgid (Adelges piceae), Woolly hemlock adelgid (Adelges tsugae), and Cooley Spruce gall adelgid (Adelges coolyi). Adelgids produce a white cotton-like appearance that covers a small, dark-colored body.  

Symptoms and Diagnosis 

They can appear as white, cottony tufts on bark, branches, twigs, needles, or cones on host plants. Cone-shaped galls, or swollen twigs, can also be found on infected spruce and fir. In large quantities, the exterior of the tree can take on a snowy appearance. Yellowing and the early dropping of needles and dieback of terminals can happen if a large enough population is present. They can stunt or kill trees if the tree is already weakened; vigorous plants can usually tolerate moderate adelgid populations.  

Life cycle 

Adelgids may feed on needles, stems, and bark by sucking the sap, where they feed can be dependent on the species of Adelgid and the host plant. Several species have alternate hosts for different life stages. Most species have several generations a year. There are several species, many of which have complex life cycles that can include alternating reproductive methods (one generation produces sexually and the next are asexual females that parthogenically reproduce). 

Integrated Pest Management Strategies 

1. Hose them off. Use a forceful stream of water to dislodge the cottony masses 

2. Clean up and dispose of swollen twigs or foliage damaged by galls before adelgids emerge  

3. Appropriate sprays can be used when the tree's health is compromised by a heavy infestation. These include horticultural oil, narrow-range oil, and insecticidal soap. Apply in the spring when crawlers are active. Be aware that using these sprays can cause discoloration on certain conifers (ie: blue spruce).  

4. Avoid excess fertilization and quick-release formulations that produce new flushes of growth that are preferred by adelgids