A lot of my potted plumerias growing outdoors for years now have these light tan or white "crystals" on the leaves. Some seem to attach into the veins like a leaf minor (which I have on my nearby lime tree) but I also have mites on my nearby tomatoes.
I was about to spray horticultural or need oil but thought to check here.
This is my 1st post: I have 4 in ground plumerias. One is a 15' tall by 25' wide Jean Moragne Jr... I assume the biggest in the area, but I also have 20 others in pots. Those are having the problem

Mealy bugs or scale probably. Check the top and bottom of the leaves this time of the year with some regularity. They suck the sap off the leaves and prefer new foliage but can be found anywhere within the plant's leaves. They can eventually kill some plants so act on it now. Put some rubbing alcohol in a cotton swab and get these pests very wet with it. Try not to get alcohol on leaves as some leaves may not like that. Dead bugs may turn brownish. Check all leaves, both sides of leaves, stems and the base of the plant and the top soil. In severe infestations, maybe consider "quarantining" the affected plants so these guys will not easily jump to healthy plants. You can also try to use some chemicals but it is probably too hot to use neem oil now and these guys cover themselves in a protective cottonish wax.

We had a few overcast days so I used a horticultural oil mixed with rosemary and clove oil mix. I also try the q-tip with alcohol on the crumbs stuck to the leaves. Thanks,

We had a few overcast days so I used a horticultural oil mixed with rosemary and clove oil mix. I also try the q-tip with alcohol on the crumbs stuck to the leaves. Thanks,