Pine Needle Scales

Pine needle scale is an armored scale that produces a white, oyster-shell-shaped, wax covering. Damage is seen as white flecks on needles or white oyster-shell-shaped scales.
Pine Needle Scales - Articles

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White flecks on Scotch pine needles (signs of a pine needle scale infestation). Courtesy of Cathy Thomas, PDA

Chionaspis pinifoliae (Fitch)

Hosts

  • Pines, especially Scotch and Mugo
  • Occasionally on Douglas-fir, true firs, and spruce

Damage Potential

  • High on Scotch pine
  • Low on other hosts

Symptoms and Signs

Throughout the Year

  • White “flecks” on needles; white, oyster-shell-shaped scales that are generally heaviest on lower branches
  • Yellowing or brown needles leading to premature needle drop
  • Heavy infestations give a frosted or silvery appearance
  • Untreated infestations may result in death of twigs, branches, and eventually the tree

Causes of Similar Symptoms

  • Needle cast diseases

Identification

Pine needle scale is an armored scale that produces a white, oyster-shell-shaped, wax covering. This characteristic covering is easiest to find on overcast days. The covering of the mature scale measures 1⁄16–1⁄8 inch (2.5–3.0 mm) in length and has a small, yellow spot on the narrow end. Male scale insects are fragile, gnatlike, and capable of short flight but are rarely seen. Female pine needle scale insects are tan with legless, wingless, flattened bodies beneath the white covering. Males do not feed. Females and immature scales have hairlike piercing mouthparts used to suck sap from needles. Pine needle scales do not produce honeydew as they feed.

The red, oval eggs are found beneath the covering of the female. Newly hatched nymphs, or crawlers, are paprika colored. Crawlers must molt and settle to feed a short time after emerging from the egg. After they settle, the mouthpart is inserted into the needle, preventing further movement. Settled nymphs are yellowish to tan. After a very short period, they begin to produce the characteristic white covering.

Biology and Life Cycle

Pine needle scale has two generations per year in Pennsylvania. Before dying in fall, each female deposits approximately 40 eggs (Figure 1). These oval, red eggs overwinter under the dead female’s covering and begin hatch by mid- to late May. Egg hatch and subsequent crawler emergence may occur over a period of 2–3 weeks. The flattened, red crawlers have legs but lack mouthparts (Figure 2). They move around on the needle and must settle and molt in a short time. Crawlers may fall from needles or be blown by air currents to infest neighboring trees. They can also be carried by insects, animals (including people), and machinery.

Figure 1. Overwintering pine needle scale eggs with dead female scale. Courtesy of Sandy Gardosik, PDA

Figure 2. Pine needle scale crawlers. Courtesy of Sandy Gardosik, PDA

Settled crawlers insert their long mouth-parts into the needle and begin to secrete the armored covering. Initially, the covering is clear or yellow, but eventually the characteristic white covering is produced (Figure 3). This generation feeds on the previous year’s growth and can readily be hidden by new growth in spring.

Figure 3. Adult female pine needle scale. Courtesy of PDA

By July, both winged males and wingless females are present. Following mating, egg laying, and hatching, the crawlers resulting from this generation move onto the current year’s needles and settle to feed. This generation is most noticeable (Fig. 4). By September, the second generation is complete and females begin to deposit overwintering eggs.

Figure 4. Mature pine needle scale population. Courtesy of Cathy Thomas, PDA

Calendar of Activities

Monitoring and Management Strategies

Plantation Establishment

  • Properly space trees; allow enough space between saleable trees.
  • Remove and destroy any mature trees in and around the plantation acting as a source for infestation.

Preseason

  • Scout for scales.
    — On an overcast day, look for scale coverings on lower branches. Pry off the scale covering with a pin and use a hand lens to look for overwintering eggs. If found, mark the tree to monitor for egg hatch.
    — Ragged chew holes or round holes in the scale covering indicate parasitoid or predator activity.
  • An application of dormant horticultural oil on infested trees may provide little to moderate success controlling overwintering eggs. Note: Oil will remove the blue color from blue spruces.

Growing Season

  • Growing degree days:
    — First-generation crawlers appear at 298–448 GDDs.
    — Second-generation crawlers appear at 1,290–1,917 GDDs.
  • Threshold level: No specific threshold information is available at this time. Populations on Scotch and Mugo pines are capable of rapid increase, but those on other hosts are generally not significant.
  • Treat if tree growth is stunted, yellowing occurs, or if scale populations become unsightly or aesthetically displeasing. Spot treat infested trees instead of treating the entire plantation.
  • Methods of scouting for crawlers (early May and early July):
    — Visit trees marked during late winter or early spring to look for crawler emergence.
    — Wrap electrical tape, sticky side out, around twigs with high populations of scales; monitor daily for the first crawler to emerge.
    — Hold a white piece of paper under a branch while shaking the branch. Look for crawlers on the paper.
  • While scouting for crawlers, always scout for predators (several lady beetle species such as twice-stabbed lady beetle, lacewings, etc.) and wasp parasitoids or evidence of their presence.
  • At the end of the season, evaluate results and update records.

Control Options

Biological

  • Encourage natural predators and parasitoids to assist with managing small infestations (Figure 5).
  • If possible, reduce insecticide use for other pests.
  • Larger infestations may not be controlled with predators alone.

Figure 5. Twice-stabbed lady beetle feeding on pine needle scales. Courtesy of Rayanne D. Lehman, PDA

Mechanical

  • Prune and destroy heavily infested branches; prune branches that are in danger of coming into contact with one another.
  • Do not mow or remove infested trees during crawler emergence as this may spread crawlers.

Biorational

  • Insect growth regulators (IGRs) can be used during the crawler stage to disrupt the molting process.

Chemical

  • Apply a spray targeting crawlers for 2–3 weeks at 7-day intervals after the first crawler is seen (most effective after egg hatch and before development of white wax covering). Note: This poses a risk to beneficial predators and parasitoids. Whenever possible, use a “softer, predator-friendly” insecticide.
  • Systemic insecticides can be effective against young, settled nymphs that have just begun feeding (June and August).

Next Crop/Prevention

  • Purchase and plant scale-free nursery stock from a reputable company.