Balsam Woolly Adelgid
|Mature female showing waxy threads with eggs.|
|Characteristic "gouting" of branch resulting from balsam woolly adelgid attack.|
Species: Adelges piceae (Ratzeburg)
Introduced from Europe around 1900, this pest is now common throughout eastern North America wherever true firs are grown. Infestations are also present along the Pacific West Coast.
All true firs, Abies, can be attacked but balsam fir and Fraser fir are the most important Christmas trees attacked.
This pest commonly stunts and kills firs. Adelgids feeding on branches and twigs cause severe gouting and prevents the growth of buds and needles. Heavy infestations on the bark of the trunk causes the formation of abnormal vascular tissue and sudden death in two to three years. The abnormal growth is called compression wood and makes the branches brittle. These snap and break off during harvest or during bailing.
Description and Life Cycle:
In North America, the balsam woolly adelgids are all females and most are wingless forms (sistentes). Adult females are a dark purple-black color and produce a thick mass of wool-like waxy strands over their bodies. The eggs are deposited into this wax. These cottony masses may be present as individuals along branches and twigs or as continuous masses coating the trunk and lower branches. This adelgid has two generations per year over most of its range with an occasional third generation. The first instar nymphs overwinter as small, uncovered, dark brown forms attached to the bark after inserting their mouth parts into the vascular system. Apparently, these nymphs can not survive winter temperatures much below -5°F. This is why best survival and highest populations usually occur on the protected areas of the lower trunk and branches. Dormant, overwintering nymphs become active in late April and molt into second instars by early May. Another two molts occur rapidly where the second instars transform to the third instar and adult stage. Spring adults are usually present by late May. The nymphs and adults are covered with the woolly waxy coating and eggs are soon deposited. Each female produces 50-200 eggs. The eggs hatch over a three week period and the new adults are present by late July. Eggs are produced throughout August and the new crawlers hatch out from August until the first frosts of winter. Remaining eggs die and settled nymphs enter a dormant state. Rarely, winged forms are produced but spread of these insects appears to be by wind blowing of the crawlers or transport on birds and other animals. Most of the initial infestations are probably the result of transport of infested seedlings.
Several predators have been imported to control this pest, but none seem to be effective. Control in Christmas tree plantations is probably best accomplished by obtaining pest free seedlings and keeping fields isolated from surrounding stands of native firs which may be infested.
Option 1: Cultural Control - Quarantine and Isolation - Since this insect rarely forms winged stages, only the crawlers can be transferred from tree to tree. Obtain adelgid free seedlings which have been grown away from larger balsam or Fraser firs. Completely harvest a field before planting new seedlings. Eggs, nymphs and adults can survive on cut trees for months so destroy any remaining cut trees or tree parts.
Option 2: Chemical Control - Pesticide Applications - Registered insecticides should be applied when the crawlers are active. The first generation of crawlers found in June are the best to treat. Thorough coverage is essential and two applications may be necessary if cool weather extends egg hatch. Oils and soaps applied to dormant nymphs have not produced satisfactory results.