Pest-control materials are another option in nurseries and landscapes. These materials are normally applied as a spray to plants and kill insects by contact. However, many also kill the natural enemies, which may lead to target pest resurgence or secondary outbreaks. Scales and mealybugs are sedentary most of their lives, vulnerable to attack by natural enemies, which may sometimes provide sufficient control. Imidacloprid kills mealybugs and soft scales but not hard scales.
Hard scales feed differently than soft scales.
Hard scales tend to burst and destroy plant cells on which they feed, often bypassing vascular tissues that transport food throughout the plant. The hard scales may not take up enough active ingredient to die.