The pine tortoise scale is sometimes a significant pest of certain species of pine. This species of soft scale overwinters as an immature circular, brown, wrinkled female on the twigs of host plants. When temperatures warm in the spring, the females begin development again. Overwintered female scales mature by June in the northern parts of the insect's distribution. Mature females are 0.24 inch in diameter and lay eggs beneath their bodies. Crawlers (immature scales) emerge by late June and early July. Crawlers are able to wander from the females and settle on new parts of the host plant, or may be distributed to new trees on the wind or stuck to birds. Many crawlers may not survive to reach a suitable host plant, however with females laying up to 500 eggs each, only a few of the progeny (young) need to survive to continue the population. There are differences in the development of the male pine tortoise scale and the female pine tortoise scale. Males feed on host plant needles for approximately one month and enter a short resting (similar to a pupal) stage. Males then emerge as tiny, winged insects capable of flight in search of female scales. Males and females mate, and shortly thereafter the males die. The mated females, which have not yet fully matured, remain on host plant twigs and enter a dormancy state in the fall at the start of cold temperatures. Mated, dormant females overwinter. A single generation occurs per year in the northern portions of this insect's range. The pine tortoise scale may be confused for a related species, the striped pine scale (Toumeyella pini). Striped pine scales have a white, median stripe on the back with scattered black pits. T. pini may be present from New York to Michigan and Florida.
Young trees are more susceptible to infestation by the pine tortoise scale than older trees, and typically the lower branches of susceptible hosts are impacted first. Needle yellowing and shortening, branch mortality, and potential tree mortality are all possible outcomes of pine tortoise scale infestation. However, a heavy population is typically required for tree mortality. This soft scale species produces large amounts of honeydew (sugary, liquid excrement), which may be colonized by black sooty mold fungi. This may cause parts of the tree or nearby surfaces to appear black in color. Primarily a pest of seedlings and saplings; may be an issue in Christmas tree plantations. Slash pine (Pinus elliottii) and spruce pine (Pinus glabra) are also hosts of the pine tortoise scale, but are found in the southeastern United States.
Monitor for crawler emergence in late June/early July, especially if a localized outbreak of pine tortoise scale is expected. Some suggest removing a section of infested branch and placing it in a clear plastic bag. Keep the bag in a shady spot outdoors, and monitor that branch for crawler emergence. This technique, or capturing crawlers with double-sided sticky tape, may make this monitoring a little easier. The results of this monitoring can then be used to time reduced risk insecticide management options that may reduce the population of the scale insects, without impacting their important natural enemy populations. If an outbreak of scales occurred in the previous season, scout trees again in the current season that had black sooty mold the previous year.
Heavily infested trees may need to be cut, removed, and destroyed, especially in plantation settings. Ant exclusion may help prevent pine tortoise scale "tending" and deterrence of natural enemies. If choosing chemical management options, select those that are least likely to impact natural enemy populations (reduced risk) that otherwise help reduce would-be damaging pine tortoise scale populations. Avoid planting seedlings or saplings near dusty roads or other similar areas, as those conditions may also deter certain natural enemies. However, the extent to which this occurs in dusty locations is not completely understood.
Predators and parasitoids generally keep the population of the native pine tortoise scale below damaging levels. Occasionally, outbreaks can occur if natural enemies are suppressed by chemical applications, dust, or fluctuating climatic conditions (Clarke, 2013). Certain families of parasitic wasps (Aphelinidae, Encyrtidae), predatory flies (Chamaemyiidae), predatory lady beetles (Coccinellidae), and predatory snout moth larvae (Pyralidae) have species that will feed on pine tortoise scales, including but not limited to: Aphytis spp., Coccophagus lycimnia, Leucopis spp., Chilocorus stigma, Hippodamia convergens, Hyperaspis signata, Encyrtus spp., Metaphycus spp., and Laetilia coccidivora (ScaleNet). Additional natural enemies are known to impact pine tortoise scale populations. In some cases, certain species of ants (Formica spp.) may "tend" pine tortoise scales, harvesting their honeydew for themselves and detering natural enemies.
Abamectin (NL)
Acephate (NL)
Acetamiprid (L)
Azadirachtin (NL)
Buprofezin (NL)
Carbaryl (L)
Chlorpyrifos (N)
Clothianidin (NL)
Cyantraniliprole (NL)
Cyfluthrin (NL)
Dinotefuran (NL)
Flonicamid+cyclaniliprole (N)
Gamma-cyhalothrin (L)
Horticultural oil (L)
Imidacloprid (L)
Insecticidal soap (NL)
Lambda-cyhalothrin (L)
Neem oil (NL)
Pyrethrin + sulfur (NL)
Pyriproxyfen (L)
Spinetoram + sulfoxaflor (N)
Dormant oil applications may be more effective at managing this scale insect when applied in the fall, and not the spring (Clarke, 2013), however follow manufacturer instructions to help reduce the chances of phytotoxicity or increased susceptibility to winter injury as a result. In that case, it may be more desirable to use spring time dormant oil applications. Otherwise, the crawler (mobile immature) life stage of this insect is most vulnerable to chemical management options.
Active ingredients that may be applied systemically include: abamectin (injection), acephate (injection), acetamiprid (injection), azadirachtin (injection, soil drench), clothianidin (soil drench), cyantraniliprole (soil drench, soil injection), dinotefuran (soil drench), imidacloprid (soil drench), and neem oil (soil drench).
When used in a nursery setting, chlorpyrifos is for quarantine use only.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
