The method Wipe off as many mealies as you can with a cloth. Then dilute 1-2 tablespoons of neem oil in 1 litre of warm water, and add a drop of mild washing-up liquid. Spray thoroughly, including on the undersides of leaves. Avoid spraying in strong sun, and test on a small area first. Repeat every 7–10 days for a few rounds, and isolate the plant while you’re treating it.