When to Manage Scale Insects on Trees and Shrubs
Always evaluate the need to treat before applying any pesticide, organic or synthetic. Plus, needlessly applying chemicals can harm the good insects that help manage garden pests.
This strategy applies to scale insects as well. Their hard-shell coverings can hang on branches for many seasons after they’ve died. Use a sewing needle to flip over the waxy coating and a hand lens for a closer look. Living scale are plump and round and often bleed when uncovered.
Check at least 25 scale insects. Multiple the number of live scale insects found in every 25 checked by 4 to calculate the percentage of live insects.
If the percent of live scale is low, a dormant oil spray applied to plants when dormant or insecticidal soap when the crawlers are active will usually provide sufficient control.
A bit more information: Consider testing scale on several parts of the plant. This provides a more accurate assessment of the live population. Treating only when necessary allows the natural enemies to help keep these pest populations under control.