Magnolia scale is also very good at killing Asian magnolias. I think you're outside the optimum treatment period now...you may have to wait until spring and treat with a systemic?

is the whole thing affected? if not just trim out the affected area. Is this one of the chinese saucer magnolias or is it cucumber magnolia?

I would not suggest "cutting it out" Scale at that density pretty much guarantees that the whole tree has a least some scale scattered through it. You'd be cutting off your foot when the infection has already past year knee. Besides, there are antibiotics that could have saved your foot.

Cutting it out not only badly affects the form of the tree, it also encourages lots of weakly attached water sprout growth in Magnolia which ironically, the scale insect prefers.

For Caldwell, the OP said it is one of the "ornamental ones" which is undoubtedly of Asian origin and they are especially susceptible to the native magnolia scale insect.

Although my sense of scale (buh-dum-bum) may be off, those scale look huge. Is that the actual size of magnolia scale? Yikes!

Yep...largest species of scale insect in North America. Up to 1/2" diameter!

i would go systemic.. when the bees go dormant ... no clue ... how to time that all out in your area ...

only downside.. dead ones look just like live ones ...

ken

What do you mean "when the bees go dormant", Ken? No, never mind.

I think that your suggestion is to apply a systemic pesticide at a time of year when bees might not be affected. Right? Knowing that systemics are found in flower nectar and pollen when we aren't very mindful of the timing.

Though your intentions are honorable and I'm all for protecting the pollinators, systemics applied to control scale insects are most effective when applied in the spring.....just in time to coincide with the bloom period.

Contact pesticides are not affective on most scale insects unless the applicator is fortunate enough to catch the 'escape' of the crawlers from under the adult shell.

Just judging on the very little bit that we've been shown, it may be a pretty bad infestation. The owner of this tree has a lot of homework to do. I'm not comfortable making suggestions without more information.

Fortunately, bees aren't common pollinators of Magnolia (& systemics would be likely be applied just after precocious Magnolias bloom anyway).

The tree is only about 12' tall. My plan is to go over the tree with dormant oil next month. If I see beneficial insects such as ladybugs I will wait 'till later on.

Be careful about the oil applications in high heat. Read the label of your product carefully; it will give the temperature limitations.

Here's a good blog regarding the natural controls of scale insects....I'm not a blog enthusiast, but this one has such good pictures! I was wanting to share information about the little parasitoid wasps that can do considerable damage to the adult scale population. Different scale species, but similar.

"(J)ust trim(ing) out the affected area" is not a good solution to this problem.