Why my cymbidium leaves are sticky?

[MaK]

Almost all my cymbidiums heavily infected by scales last fall and I used Garden Safe 3in1 to control the insects. That product works very well. It's contained neem oil, and later combined with dust, so sticky residue left on the leaves. I noticed when I touch the leaves but can't visible. Do I need to wash it off or leave it? Give me a some suggestion if you have same experience. Thank you.

MaK, SF.CA