Hi John! Your service provider told you the right thing. Spring is when the scale nymphs begin to really suck out the sap from the trees. In early May, a soil drench (the systemic drench) is applied. This is the most effective control for Magnolia Scale.

By early summer, the females start to be covered w/a powdery, white, waxy coating. So spraying them at that point doesn't work. In late July-early August, the females give birth and the "crawlers" find a place to overwinter. In late August, you can use a horticultural oil (probably what the provider called the "fall dormant service") to spray on the crawlers. This can also be done in October-November and in early March.  You need to thoroughly wet the stems, leaves, & branches. If you spray in early March, please watch the flower buds. If they are starting to swell, like they're going to open, the spray can damage the buds.

Remember, when using chemicals, the label is the law. You are required to follow all instructions. Please wear/use PPE like gloves, long sleeves & pants, eye protection, & even a mask (we all have them now) so you don't breathe in the chemical.

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