Scale insects are a large family that feed on a wide range of host plants and have many different appearances. Scale is usually divided into two categories: armored and soft body scale. Armored scale insects, in the adult stage, have a hard outer cover that makes treatment timing critical. All scale insects have a series of growth stages that they experience at different times of the year. Control methods depend on catching the pest at a certain stage in their life. The type of scale insect present on the host plant will determine the proper treatment needed to control the scale.

While there are a wide variety of scale species, the damage they cause is similar. Scale insects pierce plant tissue and remove plant sap by sucking it through their mouthparts. Damage to the host plant includes leaf yellowing, reduced plant growth and branch dieback. While soft body scale species are feeding they excrete a sticky substance called honeydew. The honeydew drips onto leaves, branches and anything below the scale. Honeydew is sticky and may cause black sooty mold to grow. Black sooty mold is a dark fungus that will grow on the honeydew. It is an unattractive and distinctive characteristic of a scale infestation.

Treatment options for scale will depend on the species. Treatment should focus on catching the scale at its vulnerable growth stage, which is typically the “crawler” stage. Scale insects are referred to as crawlers during their juvenile life stage. For armored scale species it’s important that control methods target the crawler stage, before the protective cover has grown over the scale. Treatment timing will vary by scale species.

Suspect scale on your plants? The PHC Department at KTS has received numerous phone calls about suspected scale infestations this spring. Call the PHC Department to have your plants accurately assessed and to receive treatment recommendations.

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