Armored & Soft Scales Information
Species & Identification
There are hundreds of scale insect species in South Carolina, with armored scales, soft scales, and mealybugs being the most common. Table 1 defines characteristics that can help differentiate these three families. Being able to distinguish between these three families will facilitate the selection of best management practices. Table 1 is not suitable for identifying species. Species identification should be completed by specialists in a private or University diagnostic lab.
Table 1: Characteristics of Scale Insect Families
| Characteristic | Armored Scales | Soft Scales | Mealybugs |
|---|---|---|---|
| Protective Shell (Scientifically known as a test) | Shell is not an integral body part. It can be separated from lower body when flipped over. | Shell is an integral part of the body. It cannot be separated from body when flipped over. | No shell. Body is covered in waxy dusts and lateral waxy filaments. |
| Honeydew production | Does not produce honeydew. | Produces large amounts of honeydew and black sooty mold. | Produces large amounts of honeydew and black sooty mold. |
| Presence of legs in adult females | Females lose legs after molting to second instars. | Females lose legs after molting to adults. | Females retain functional legs throughout life. |
| Shell attachment to plant material | Shell always fastened to plant materials. | Shells fastened to plant material just prior to egg production. | Mobile for entire life. |
Damage & Symptoms
Scale insects are piercing and sucking insects, meaning they feed by puncturing into plant tissues with their straw- or needle-like mouths and sucking out cell contents or phloem. They often cause chlorosis (yellowing or discoloration of leaves) and, in some cases, can cause pre-mature leaf drops. Depending on the severity of the infestation, plant parts may become distorted or even die. When soft scales or mealybugs are present, honeydew deposits (appear as shiny and sticky droplets on surfaces) and black sooty mold will be apparent.
Life Cycle
Females lay anywhere from 100 to 1,000 or more eggs depending on the species. The hatchlings, commonly known as the crawlers, move away from their mothers and find their own feeding sites. Crawlers will molt into nymphs, which continue feeding and developing to adults. Females of armored and soft scales lose their legs as they mature. Females die after laying eggs, which are protected under the females’ shells. Many species reproduce asexually, i.e., the females can lay eggs without mating. Males are few in number in species that reproduce sexually. Female scale insects do not have a clear division of body segments. Adult males look like gnats, with fragile bodies, one pair of wings and antennae, and wax filaments projecting from the rear end of their bodies. Adult males live for only a few days and die after mating.
Scouting
Scouting for crawlers, which are most susceptible to insecticide treatment, is essential to achieving optimal control of scale insects. There are three methods to inform when scouting should begin: calendar date, a growing degree-day model, or a plant phenological indicator. Some well-research species have known dates when egg hatch occurs. Calendar date monitoring may not provide the most accurate prediction of crawler emergence because scale insect life cycle may be delayed by cooler weather or accelerated when warmer. Growing degree-day models and plant phenological indicators, which correlate with temperature, may provide more accurate predictions. Speak with a local Extension agent to help identify what phenological indicators or degree-day models are best for your location.
Cultural Control
Scale insect infestations are more damaging on trees and shrubs that are not planted properly or suffering from poor site preparation, poor site (or plant species) selection, diseases or other planting or maintenance practices. Keep plants as healthy as possible by following best planting and maintenance practices. Do not over-fertilize plants; scale insects are known to benefit from increased fertilization. Provide supplemental irrigation during drought. Conserve soil moisture with mulching. Prune out infested branches if the infestation is isolated to a small portion of the plant. The pruned branches should be removed from the site and destroyed to prevent the scale insect crawlers from moving back onto the plants.
Chemical Control
A large number of insecticides are available for the management of scale insects. However, not all insecticides are equally effective against all scale insect species. Insecticide selection should be made based on the feeding habit of the target scale insect species.
