The fluffy white material is part of the "shell" (body covering) produced by the scale insect, and it's more visible on male scale of this species than the females. It's a waxy material that helps keep the insect more protected from the weather (including desiccation) and from predators. Juvenile male White Prunicola Scale tend to cluster together on the lower branches, which is why they are the most prominent part of an infestation. Remove female scale as well, if you can find them, though they are a bit more camouflaged. Eggs are laid under the female's body, which is hidden from view by her cover/shell, so whether she is gravid (full of eggs) or not probably won't have an impact on the amount of white wax surrounding her cover.

Anything that you can use to scrub scale off the bark is fine (even damaging them without removing them entirely is probably enough, as the dormant oil does the rest to help suffocate them), as long as it doesn't abrade away the bark itself. A produce or dish scrub brush is probably effective since the bark of cherrylaurel isn't super thin.

Miri

You're welcome!

Hi – I hope you don’t mind a few more questions!

- I’m thinking of spraying with a dormant application of Neem now, and then again in the late winter. Is there any reason not to do that?

- How long does it take for the oil to smother the gravid female? Does it happen quickly, take days? We’re oddly curious about this scale.

- Today I used the hose sprayer (on the "jet" setting) to spray more of the females (the round things) off the branches. A lot came off! Do you think most of these are gravid females, or old casings that probably come off easier? (I ask because I don’t want to waste time and water spraying off just casings).

- Finally, we were thinking that over the winter, on nice days, we’d periodically go brush the scale off the branches. Is there any risk to the plant if we do that in the winter? Yes, we need to get more hobbies!

Many thanks!

Neem oil might not be available in a dormant oil concentration, so just verify that the product you chose has the option to dilute the material at the right concentration to make it "dormant oil" instead of a "summer rate" oil. Granted, it's a tiny difference in concentration, but it is an important distinction to both have it be as effective as possible while avoiding damaging the plant itself. Neem is only one type of oil in the "horticultural oil" category, and often products sold for dormant oil use use mineral oil or another form of horticultural-use oil.

Our horticultural oil information page includes some details about application caveats or restrictions, including temperature guidelines. The product label has the final say, as it bears the weight of Federal law (pesticide products must be used as the label states), but generally, the temperatures need to be mild enough that the insects are respiring (breathing) enough that being smothered with oil is actually going to suffocate them. (Insect development and metabolism is highly dependent on ambient temperatures, since they are cold-blooded organisms. They therefore won't respire nearly as much when it's cold as when it's mild, so if they already aren't taking in much oxygen during a cold spell, spraying them during that time won't accomplish much before the oil evaporates enough to be rendered no longer effective.)

We don't have information specific to how long each application remains effective, as it will partly depend on how quickly the oil evaporates. Several applications of any pesticide used for scale may be needed regardless, though, as it will be difficult to contact all scale in just one application, especially with a contact-type spray like horticultural/dormant oil. Dead scale don't necessarily fall off the plant right away or even look that different (unless the oil helped to remove most of the white wax in their body covering), so it can be difficult to tell over the short term if a treatment is working. The better indication would be that scale don't seem to be spreading (on the same plant, or onto neighboring cherrylaurel) and the plant isn't developing dieback any longer, though to be fair, issues unrelated to the scale could contribute to dieback.

Scale are small enough that microscopic examination (or at least strong magnification) is usually needed to determine the insect's life stage and whether it's alive or dead. It's good that many detached when you sprayed them (whether alive or dead, their removal is a good thing), and even removing dead scale can be helpful for monitoring, since it helps you determine if a population is growing again or not.

No, there's no need to worry about brushing/scraping off more scale as you see fit over the winter. As long as you aren't cutting into the bark itself and exposing the sapwood underneath (unlikely unless you use a very strong pressure washer direct spray or use something sturdier than a scrub brush), it won't matter what time of year you do that, or how often.

Miri

You're welcome!