I purchased a calomondin bush for a friend whose plant I accidentally killed when I exposed it to scale.
Upon bringing the new plant home, I now realize there is a white dusts on the leaves. Now I’m worried the replacement plant is sick! Please help- is this normal or is this a plant problem!?
Thank you for contacting Toronto Master Gardeners.
The Calamondin is a hybrid cross between a tangerine, a mandarin and a kumquat.
It is a strong plant which prefers to be outside but is able to grow well indoors . The Calamondin is susceptible to only a few diseases. One is scale which you have previously experienced and the other is mites.
From the picture I do not believe you have mites. With mites you would see yellowing leaves and sometimes small webs and the plant would look sickly. To be absolutely sure you can put a white paper underneath and shake the branch. If there are mites they will fall on the paper.
Another occasional issue is powdery mildew but that would be much more pronounced. I think what you are seeing is a residue left over from something the nursery sprayed on the leaves. They can be hard to wash off as they are not always water soluble. If you want to be sure it is not something that is spreading you can take a picture a day or two apart and see if the marks remain exactly the same.
I have attached a link below for you in case you would like to do further research on this plant.