I have a Philodendron and two tropical plants that were in my kitchen bay window. I noticed a white powdery material on the leaves of the plants that were together, not on the ones separated. The powder was on the top and bottom of the leaves but was easily removed when wiped with a damp cloth. What could this be?
Disease on House Plants
Certified GKH Gardening Expert
Neem oil will work well on powdery mildew problems. You can read more about this oil here: https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
You can also find other home remedies for powdery mildew here: https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm
If the white stuff is soft and cotton-like, then it is a mealybug infestation. Treat it by thoroughly by spraying with a solution of 5 parts water, 1 part alcohol and a squirt of liquid dish soap. The key is to spray all leaf and stems surfaces of the entire plant until they are dripping wet.