They look like they are from the Coccidae group of soft scales.
There are several sprays for control...... the safest for organic control is the Fatty Acid types.
These are the insecticidal soaps that you can get from the garden centres. They break down the waxy coating that the scales produce.
Please avoid using things like Pyrethrum if you can.
Although these will do a good job, they will also control the predators that are trying to help you too.