How Can I Control Scale Insects?

Do you want to control scales using the biological control method?

Do you want to control scales using low-risk (organic) insecticides?

Do you want to control scales using synthetic insecticides?

Do you want to use residual, foliar sprays?

Commercially available beneficial insects, like ladybugs and lacewing, are natural predators of the young larval or “crawler” scale stage. The most important natural enemies of scales are parasitic wasps, including species of Aphytis, Coccophagus, Encarsia, and Metaphycus. However, because ants attack and feed on scale parasites and predators, you need to control ants before attracting or releasing scale predators. To deny ants access to plant canopies, prune branches or weeds that provide a bridge between buildings or the ground and apply a sticky material (Tanglefoot) to trunks.

Organic pesticides, like insecticidal soap and d-Limonene can be used to kill the larvae. However, these products have very little persistence in the environment, so several applications during egg-hatching will be required for effective control. Horticultural oils and other safe, oil-based insecticides work by smothering insects and will control all pest stages, including adults which are protected from most other insecticides by their armor coverings. You'll need to follow product labels, which may say to not spray certain plant species or mix oil with certain other products.

Foliar sprays of broad-spectrum insecticides with residues that can persist for weeks are not recommended for scale control in landscapes and gardens. Pesticides to avoid include carbamates, nonsystemic organophosphates, and pyrethroids. These are highly toxic to natural enemies and pollinators and can cause outbreaks of spider mites or other pests. Because their use in landscapes and gardens can run or wash off into storm drains and contaminate municipal wastewater, these insecticides are being found in surface water and are adversely affecting nontarget, aquatic organisms.

Systemic (absorbed by one plant part and moved to leaves and other plant parts) insecticides for use on landscape plants include neonicotinoids (acetamiprid, dinotefuran, imidacloprid, and thiamethoxam) and the organophosphate acephate (Lilly Miller Ready-to-Use Systemic, Orthene). Properly applied, one application of an effective product may provide season-long control. However, neonicotinoids vary in effectiveness for scale control. Do not apply systemic insecticides to plants during flowering or shortly before flowering. Follow product labels and learn about specific scale species to avoid using non-effective insecticide.

Provide plants with good growing conditions and proper cultural care, especially appropriate irrigation, so they are more resistant to scale damage. You can prune off heavily infested twigs and branches if they are limited to a few parts of small plants. In areas with hot summers, pruning to open up canopies can reduce populations of black scale, citricola scale, cottony cushion scale, and possibly other scales by increasing scale mortality from exposure to heat and parasites.