Spathyphyllum – Scale
Q: A departed co-worker left me three large spathiphyllum (Peace Lily) plants. One appears very healthy. The other two have serious problems. The leaves are coated with a shiny, sticky crystal.
It looks like somebody sprayed the plant with a can of Sprite and it dried on it. The stems also have small brown spots/growths on them. They seem to flake off very easily.
A: Wow – it’s scale insects of some sort and LOTS of them!
The leaves are shiny because scale can’t digest all of the sap they suck out of the leaves. What they can’t use they excrete…and that’s what’s on your leaves.
Honestly, I’d discard all three plants. The chances of the healthy one NOT being infested are small. You’d likely spend a lot of time trying to keep the scale under control.
If you want to try to keep them, imidacloprid (Bayer Insect Control plus Fertilizer plant spikes) is a good systemic insecticide.
But I think it would be better to buy new, clean plants.