Chlorotic damage from elongate hemlock scale feeding on the undersides of needles. Courtesy of Sandy Gardosik, PDA
Fiorinia externa Ferris
In southern and Mid-Atlantic states, two overlapping generations have been reported, while in states in the Northeast, a single generation is known.
- Fir (Abies spp.)
- Hemlock (Tsuga spp.)
- Occasionally found on spruce (Picea spp.), Douglas-fir (Pseudotsuga menziesii), and pines (Pinus spp.)
Symptoms and Signs
- Yellowing of needles on the interior of the lower branches; damage moves upward as population increases
- Scale coverings on the underside of the needles
- Premature needle drop; eventual branch and limb dieback and death of tree with severe infestations
- Tree may appear flocked
Causes of Similar Symptoms
- Spruce spider mite
- Cryptomeria scale
Elongate hemlock scale—sometimes referred to as Fiorinia scale—is an armored scale found more prevalently in southeastern Pennsylvania. Translucent, oval eggs occur beneath the scale covering of the female. The pale yellow crawlers are about 1⁄250 inch (0.1 mm) long and have six short legs. When they settle to feed, the crawlers lose their legs and excrete an amber-colored, oval covering. Male and female scales develop differently and have different protective coverings. Immature males are about 1⁄20 inch (1.0–1.5 mm) long and produce a whitened, waxy covering. Longer threads of wax are occasionally present and may give the covering a fuzzy appearance. Immature females are longer at 1⁄14 inch (1.5–2.0 mm) and produce a yellowish to orange-brown, parallel-sided covering. At maturity, the delicate, light brown, male scales emerge and fly to the sessile, wingless females. They may be mistaken for parasitoids as they crawl over the female coverings prior to mating.
Biology and Life Cycle
Elongate hemlock scale overwinters in several developmental stages in Pennsylvania and matures in spring (Figures 1 and 2). In southern and Mid-Atlantic states, two overlapping generations have been reported, while in states in the Northeast, a single generation is known. In Pennsylvania, reproduction is staggered, so crawlers are present throughout the growing season.
Figure 1. Heavy infestation of elongate hemlock scale. Courtesy of PDA
Figure 2. Female (brown) and male (white) scales. Courtesy of Sandy Gardosik, PDA
Calendar of Activities
The first egg hatch generally starts in late May or early June. Mobile crawlers move from under the female’s covering to the underside of needles (Figure 3) and begin to feed by inserting their piercing-sucking mouthparts. This feeding causes chlorotic, or yellow, spotting on the upper needle surface (Figure 4). At the same time, the crawlers begin to secrete a translucent, waxy covering. Mature females are present about 6–8 weeks after emerging (Figure 5). Male scales molt an additional time before the winged stage emerges (Figure 6 and 7). Following mating, the males die and the female begins to produce about 12–16 eggs under her armored covering (Figure 8) As a result of the various overwintering stages in Pennsylvania, crawlers emerge throughout the growing season, making repeated control efforts a necessity.
Figure 3. Female scales and mobile yellow crawlers on the needles. Courtesy of Sandy Gardosik, PDA
Figure 4. Chlorotic scale feeding damage on grand fir. Courtesy of Cathy Thomas, PDA
Figure 5. Female elongate hemlock scale. Courtesy of Sandy Gardosik, PDA
Figure 6. Immature male elongate hemlock scales. Courtesy of Sandy Gardosik, PDA
Figure 7. Adult male elongate hemlock scale. Courtesy of Jim Stimmel, PDA
Figure 8. Eggs inside the overturned female elongate hemlock scale casing. Courtesy of Sandy Gardosik, PDA
Monitoring and Management Strategies
- Plant tree species that are not susceptible to elongate hemlock scale.
- Properly space trees when planting to minimize infestation from tree to tree and enable thorough coverage if chemical controls are used.
- Weed management is important to expose lower branches for ease of detection and effective control.
- Remove and destroy any mature host trees that may serve as source of infestation. (Canada hemlock is a common host in Pennsylvania.)
- Limit the use of nitrogen fertilizers; nitrogen enhances survival and developmental rate of scales.
- Scout for elongate hemlock scale on the underside of needles. Note: Sometimes a combined population of Cryptomeria scale, balsam woolly adelgid, and hemlock scale can be found on the same trees.
- If only a few infested trees are found, removing and destroying them before bud break may prevent a serious infestation from developing.
- If numerous infested trees are located, tag a few to use for observations of crawler emergence.
- Place sticky cards on branches showing symptoms to trap adult male scale insects (Figure 9). Their emergence signals that eggs will soon follow.
Figure 9. Yellow sticky cards used to attract the emerging male elongate hemlock scales. Courtesy of Cathy Thomas, PDA
- Starting in mid-May, scout tagged trees every few days to check for crawler emergence.
- Growing degree days: Crawlers are active from 360 to 700 GDDs.
- Threshold level: No specific threshold level exists at this time. However, dieback of major limbs tends to occur by the time the population reaches ten scales per needle.
- Continue scouting for crawlers every few weeks to determine the need for additional controls.
- At the end of the season, evaluate results and update records.
- Encourage natural predators such as lady beetles, parasitic wasps, and several lacewing species.
- Avoid applications of broad-spectrum insecticides that will kill natural predators.
- Remove and destroy heavily infested trees before bud break. Wrap trees in a tarp/plastic when dragging them through the field to prevent transferring scales to other trees.
- Clean mower blades or tractors when moving them from an infected field to an uninfected field.
- Butt-prune infested trees to remove the most heavily infested lower branches.
- No recommendations are available at this time.
- Horticultural oil may be applied during the growing season. Use lower rate to avoid damage to new growth or wait to apply until new growth has hardened off.
- When first crawlers are active, apply a systemic insecticide spray three to four times over a 12-week period (three sprays four weeks apart or four sprays three weeks apart). Do not apply more than four times per season.
- Evaluate each application to determine the need for subsequent sprays.
- Purchase and plant scale-free nursery stock from a reputable company.