I have 3 arrowhead plants with northern light, no direct sun. One of them has developed white flecks, like "ashes" on leaves. It wipes off but returns. What is it and how can I treat it?
This is likely Mealybug infestation. Neem Oil can be used to treat the plant. Mealbug can be stubborn and you may need multiple treatments.
I would recommend even dotting the 'spots' with Neem Oil using a Q tip.
Here are some links for you.