Homemade Summer Oil for Camellia Scale?

I have a camellia with a moderate scale/sooty mould problem. We have removed almost all the mould with soapy water and want to treat the scale before it infects the new leaves. I would like to make my own "summer oil" treatment and wonder whether I can use mustard oil for this purpose? I've used it full strength on houseplant leaves to repel cats and on bulbs to repel squirrels and it never seemed to bother the plants.
One recipe I've seen called for 1-4% summer oil in water and another from a Roedale book said to mix 1 cup cooking oil with 1 tbsp liquid soap and apply resulting blend at a rate of 2 1/2 tsp per cup of water or about 5%. We cook with olive oil which I don't think has much insecticidal effect and I don't want to buy cottonseed or canola oil if I can just use the mustard oil I already have. Does anyone know if matters what kind of oil you use?

 

Test what you want to use on a few leaves on a hot sunny day first and you will find out first hand about toxicity to the plant. I have no idea if the oil mixture you want to use will last long enough.

Oils are used to suffocate insect eggs and scales and require a length of time to be present. If you are applying your oil to scale shells, do make sure they are not empty. You cannot suffocate a host that isn't there.

Jim.