Scale insect on Physocarpus

I have just discovered a large infestation of scale insect on Physocarpus opulifolius 'Diabolo'. Has anyone else had this problem and can anyone give advice on the best steps to take please?
I try to garden organically, so want to avoid using strong insecticides if at all possible. An alternative seems to be to cut it down to the ground and let it sprout again, but it is full of bud and about to flower. It seems unaffected by the infestation, but nevertheless I don't want it to spread to the fruit trees and shrubs nearby. I wonder whether these insects are species or genus specific? - in which case I could let it flower before a severe haircut.....

Any advice and suggestions gratefully received

I don't know if it's available in France, but Bayer makes an excellent systemic insecticide that is derived from tobacco (nicotine), so it's pretty much "organic". It's called Bayer 12-month Tree and Shrub Insect Control and Fertilizer. It's works wonderfully well and you have to apply it (mix and pour around the base) only once per year. In this country, it's readily available and very inexpensive. (see photo)

Alternatively, you can apply a summer-weight horticultural-grade oil to the plant. It's completely organic and should smother the scale, especially the babies at the crawler stage.

Note: Are you sure it's a scale infestation? Ninebarks are notoriously pest-free.

Thanks so much for the suggestions I'll have a look and see if I can find either of those here, they sound excellent solutions.

Yes, I was astonished to see the plant covered with scale and had a closer look in case it was some weird outgrowth from the plant. Unfortunately it is definitely scale insect :( and I can slide them sideways to unglue them. They leave a whitish mark where they were attached. They can then be squashed. They are slightly translucent with the light behind them and are symmetrically marked with a line down the centre of the back.
The plant is smothered in them but I can find no signs of any on nearby shrubs and fruit trees, so I wonder if this particular scale only parasitises ninebark.

Yes, most unusual. The only pest on ninebarks in this area is a fungus that attacks them in really wet weather. Otherwise, no problem. Good luck with treating them. Remember that spraying pesticides have no affect on scale insects because of their hard "shell". You have to get to them either by a systemic or smother them with oil.

Yes, spraying is all the rage here, but I'll hunt this down hopefully. Bayer are here, but I can't see the equivalent on their website, though there is one candidate where the details are not displaying properly. It doesn't seem to include the fertiliser element and I can't tell how it is applied. Thanks very much for your help. I'll keep you posted :)

I couldn't get the one you suggest. They don't do anything to water in so I bought a new product by Bayer specifically for scale. It's sprayed on but does act systemically. That will keep me going, but I'll see if they do the one you suggest in England and, if so, get a friend to bring me some perhaps. It sounds really good.