What's at the Bottom of My Vandas

[c123anderson]

I am trying to figure out what I'm seeing at the bottom of some of my vandas. I've included two pictures of the same plant. What it appears like is almost a fraying/ruffles on the edges of the leaves.

Background: mealybugs found and treated with insecticide (4x at weekly intervals, rotating types.)

Is this 1) insecticide residue, 2) burned leaf/roots, 3) damaged plant, 4) mealybugs?

I am using isoprophyl alcohol on a swab to treat in case it's still mealybugs. I'm afraid it's drying the leafs out and causing this.

Note: I'm also noticing something similar on my cymbidium. Not all my vandas are having this issue, though. And I'm not seeing other evidence of current mealybugs, just leftover damage.

And I posted in this forum 1) mealybugs addressed here earlier and 2) is it possibly some other pest or disease.