What's the most effective way to eliminate scale infestations?

Eradicating scale populations requires perfect timing. I have saved citrus trees simply by timing my action on crawlers as they emerged from scale populations into a brief mobile stage during the spring. The insects are light-colored nymphs that are easily identified at this immature stage. You should apply insecticidal soap directly at this time. The soap will permeate their soft bodies, killing them, before they develop a protective scale for their bodies.

Horticultural oil suffocates adult scales by plugging their spiracles. Use dormant oil before the buds break in early spring. During the summer, you can use a lighter oil without stressing the plants. In my experience, complete coverage of the oil is more important than its concentration. Any missed areas will eventually become reinfested.

Use lady beetles as a sustainable measure for pest control and bring them out when you first see crawlers from the magnolia scale on your magnolias. Each of these predators can consume over 50 scales each day. I have maintained a population of beetles by avoiding the application of broad-spectrum pesticides. With consistent use of lady beetles, my infestation of magnolia scale has decreased at least 80% in just two seasons.

If you are experiencing heavy infestations, it is best to combine methods. First, prune any heavily infested wood, and spray the crawlers with soap spray. You can follow these applications with oil sprays while the wood is dormant. Once you have performed these applications, you will need to monitor the plants by applying tape tests to check for new crawlers. This was the integrated approach I took to eliminate scales from my greenhouse.

Read the full article: Mastering Scale Insect Identification: A Complete Guide