Magnolia scale is treated with horticultural oil timed to two windows: late summer, once the young crawlers have settled, and the dormant season in fall and early spring. Timing decides the result, because insecticide sprays work on freshly settled crawlers but have little effect before the crawlers appear.

Why does timing matter so much with magnolia scale?

Because the insects are exposed for only a short part of the year. Magnolia scale spends the winter on one to two year old twigs as tiny, dark nymphs, and the females grow into shiny, tan brown shells nearly half an inch across. In late July and August they give birth to crawlers, the young, mobile stage that sprays reach most easily.

When should a magnolia be sprayed for scale?

In late August to early September, after the crawlers have settled, and again in October to November and in March to kill the overwintering nymphs. To catch the crawlers once they settle, Horticultural Oil Insect Spray is sprayed onto the trunk and branches until stems and leaves are thoroughly wet, and never while the tree is in flower.

The guide comparing horticultural oil and neem oil for scale covers the dormant and growing season dilutions.

Does treating the scale clear the black sooty mold?

Not on its own. Controlling the scale stops new sooty mold from forming, because the mold grows on the sticky honeydew the insects excrete, while the mold already on the leaves is covered in the guide to black magnolia leaves.

Frequently Asked Questions

Can a magnolia get a dormant spray in March if its buds are swelling?

No. Flower buds can be damaged once they begin to swell, so the buds are checked before any spring dormant spray.

Is there an option for a magnolia too large to spray thoroughly?

Yes. Once A Year Insecticidal Drench w/Merit, a systemic insecticide mixed with water and poured at the base, is taken up by the roots and protects the tree for 12 months.

Do natural predators keep magnolia scale in check?

Rarely. Predators and parasites exist but seldom control the scale well, especially on smaller magnolias.

Which magnolias does this scale attack most?

Saucer, star, lily, and cucumber tree magnolias are the most commonly attacked.

How can a magnolia scale be kept off a new tree?

By inspecting the branches before buying and skipping any plant that still carries old scale shells.