Magnolia Scale: Take a Look!


"Take a Look!"

“Take a look”, I said to my concerned client, as we stood in the shade of her Magnolia tree. I had just handed her my hand lens, and I showed her how to get it close to her eye as she peered through it. I wanted her to see what was in my hand – a dead adult Magnolia scale insect.  Recently dead, which meant that the crawlers should already have emerged.

When I first looked at this tree, I expected to find crawlers on the stems but was surprised that there weren’t any. "This time of year - they should already be out",  I said to myself as I let my client examine what I had just picked off her tree. My thoughts were interrupted by a low cry of consternation: “José, they’re crawling all over your hand!  You have to wash your  hands right away!”

Ugh. She was right. They were way too small to feel, but I could certainly see small black specs on my fingers, and they were covering ground pretty quickly.  As we moved toward the garden hose, I was thinking: Those eggs had to have hatched out days or weeks ago, but they are only now emerging from under the adult? Why have they waited this long?  Scale insects are the worst and they often throw us these curve balls…

Magnolia Scale: A Summary

Most people don’t realize they are even looking at an insect when they see a scale on a plant. It is an insect that forms a sort of shell, some hard, some soft, over itself. Immobile, it sucks the sap out of a plant, lays eggs, and dies, mostly unnoticed. That is until their numbers grow so large that the plant may decline or parts of the plant may die, sooty mold grows on the honeydew excreted by the scale insect, and flies start buzzing around the honeydew as well. Then folks start wondering what in the world is going on with this plant?

Magnolia scale is very host specific, meaning that it affects Magnolia species almost exclusively.  It is the largest scale insect in our area, sometimes as large as a dime. The adult in its prime is very white, and soft when pressed.  It can be very messy if squished. Be warned. Mechanical pressure is one way to kill this pest, but that pressure usually requires hands and fingers. Not an effort for the faint of heart.

There is one generation per year, which usually indicates the pest can be controlled more easily. As with all scale insects, experience proves control to be a process of perseverance over time. The most vulnerable stage is the newly hatched nymph stage, the mobile stage we call a “crawler”. At this point, the insect has still not formed its waxy covering and will be killed if contacted with the appropriate insecticide.

Nymphs emerging from a recently plucked adult Magnolia Scale

Nymphs emerging from a recently plucked adult Magnolia Scale

As I write this, eggs have hatched, nymphs have emerged, and some are still emerging.  Ken has captured some great footage of this very process, something I have never seen recorded before.  Thanks for sharing Ken!

(Technical notes gathered from experience, general knowledge, and from Insects that Feed on Trees and Shrubs, second edition, Johnson and Lyon.)

Your friendly neighborhood arborist, 

José Fernández