Swelling, or gouting, on branches resulting from abnormal cell growth caused by adelgid chemical secretion. Courtesy of USDA Forest Service Region 8 Archive, Bugwood.org (#1510051)
Adelges piceae (Ratzeburg)
The immature nymphs overwinter on the trunk, larger branches, and around buds.
- Flat top or crooked terminal
- Gouting (swelling) around buds and internodes
- Stiff, inflexible trunk and large lateral branches
- White, cottony masses on trunk and large branches
- Dead shoots or branches (red or brown needles)
Causes of Similar Symptoms
Balsam woolly adelgid females are softbodied, spherical, purplish-black, wingless insects. They are about 1⁄25 inch long (< 1 mm) and are not mobile. During the winter, immature nymphs can be found on bark. They are dark and have white, waxy rods down their backs and around the edges of their bodies. At this stage, they closely resemble the eggs of balsam twig aphid. As the mature, they continue to secrete this waxy substance, which gives them a covering that may cause them to resemble minute cotton balls by the time females are present. Eggs are oblong and deposited in a cluster behind the female. The orange-brown crawlers are the only stage with functional legs. Red eyespots are also visible on the crawlers. A hand lens is needed to effectively locate all stages.
Symptoms can be helpful in detecting balsam woolly adelgid, but it may take several months for damage to become visible. Symptoms develop slowly since the insect only feeds on the bark, not the needles. When a tree begins to show symptoms, it means that the tree has been infected since before bud break of that growing season. The first most noticeable symptom is a fl at top or weak, crooked terminal. As the infestation progresses, trees may have swelling, or gouting, around the buds and shoot nodes. The swollen growth is a result of a chemical inserted as the adelgid feeds on the branches. When adelgids feed on the main trunk, they cause the tree to become brittle due to the formation of scar tissue. When harvesting, examine stumps for this dark ring of wood.
Biology and Life Cycle
No male balsam woolly adelgids are present in North America. Females reproduce parthenogenetically (by producing eggs that are exact clones of the adult). The immature nymphs overwinter on the trunk, larger branches, and around buds. In early spring, they mature and the female adelgids are present. Females cover themselves with waxy, wool-like covering—hence the name balsam woolly adelgid (Figure 1).
Figure 1. Adelgids covered with a protective white, woolly wax. Courtesy of USDA Forest Service Region 8 Archive, Bugwood.org (#1510053)
Calendar of Activities
Each female produces a cluster of eggs under the woolly mass surrounding her body (Figure 2). Up to 200 eggs can be produced in the laboratory, but in the field the number of eggs is reduced and depends on the condition of the host tree. Eggs hatch in about a month, around the time of bud break.
Figure 2. Cluster of eggs produced by females under white, woolly wax. Courtesy of Scott Tunnock, USDA Forest Service, Bugwood.org (#2252066b)
When crawlers emerge, they can live up to 2 days while searching for a place to settle. Since crawlers lack mouthparts, they must molt before feeding can begin. These nymphs insert their piercing-sucking mouthparts into the bark to feed, but, once inserted, the adelgid is not able to move. While feeding, adelgids secrete a chemical that causes the abnormal growth of cells in the area. This leads to swelling or gouting, branch dieback, and possible death of the tree (Figure 3). The stationary crawlers will molt several times before becoming adults. In midsummer, these adults lay eggs, which again hatch into crawlers. The crawlers overwinter and start the cycle again the following spring (Figure 4). In Pennsylvania, two generations occur per year.
Figure 3. Gouting, or swelling, from growth of cells in the area. Courtesy of Robert L. Anderson, USDA Forest Service, Bugwood.org (#1748038)
Figure 4. Overwintering balsam woolly adelgid nymphs. Courtesy of Rayanne D. Lehman, PDA
Monitoring and Management Strategies
- Remove and destroy unmanaged fir that may act as a source of inoculum.
- Purchase and plant pest-free stock from a reputable nursery.
- Scout at waist height for adelgid symptoms on branches (swollen areas) and main trunk (white, cottony masses). Look for flat tops on trees or dark reddish rings in wood of cut stumps.
- Maintain good weed control.
- Butt-prune trees when appropriate.
- Scout for adult adelgids in late spring through late summer. Look for the white, waxy, wool-like covering, remove suspected area, and examine it with a hand lens or under a microscope to confirm adelgid infestation.
- Tag any infested or suspected trees.
- Scout for terminal damage in fall after tree growth has ended for the season. Look for flat tops by walking back and forth through rows spaced 6–10 feet (1.83–3.05 m) apart. If a suspect tree is found, rock the tree back and forth to check for a stiff trunk. If not confirmed, flag the tree and recheck in about a month.
- If the adelgid is found, treat the field before bud break of the following season. Treat after harvesting any trees from field and possibly time with other pest treatments (e.g., with balsam twig aphid control).
- Examine stumps from the current season for evidence of scar tissue.
- At the end of the season, evaluate results and update records.
- Several foreign predators have been introduced, although the level of control they provide is still unclear. Aphidecta obliterate (L.), Laricobius erichsonii (Rosenhauer), and Pullus impexus (Mulsant) are beetles. Aphidoletes thompsoni Mohn, Cremifania nigrocellulata (Czerny), and Leucopis obscura Haliday are flies.
- Cut and burn heavily infested trees that will not be salable. Do not cut during crawler activity.
- Clear-cut infested blocks.
- Horticultural oil spray: apply thoroughly to the trunk and bark of large branches in late fall, winter, or early spring; oil can damage foliage if not applied properly.
— Only apply oil when temperatures are above freezing.
— Oil will remove “bloom,” or blue color, from blue specimens.
- Use a high-pressure sprayer to apply an appropriate insecticide during the first generation-crawler stage; fully cover all trees to achieve the best control. Note: Control for balsam woolly adelgid may kill natural predators of other pests.
- Scout one month after treatment to make sure adelgids are dead; look for new woolly spots.
- Scout every year to determine if and when treatment or re-treatment is necessary.