Hello, I have a number of house plants in containers that I have had for years (I don’t know what they are called but I have attached pics below). I have just noticed recently, have this white powdery spots on it; they almost look like lint. It doesn’t seem to be hurting the plant but not sure what it is and if there’s a long term effect.
These spots are found both on the stems of the plants and leaves of multiple plants in multiple spots throughout the condo, along a sunny window full of sun and also out of direct sun.
We live in Humber Bay Park in a condo high up south/east facing the lake. I do keep humidifiers on year round, not sure if humidity has anything to do with it.
Thank you for getting in touch with the Toronto Master Gardeners. You’ve attached an excellent picture of the “white powdery spots” that you describe as being on several of your plants.
The powdery spots are actually female mealybugs, a common pest of houseplants; they loosely attach themselves to stems and leaves of plants and cause damage to the plants by sucking the juice from the host plant. The leaves may turn yellow with time and eventually drop off. Of course, once one has visually detected mealybugs on plants, treating and controlling the infestation is important to prevent their spread. Mealybugs tend to be attracted to plants with soft growth that have been over-fertilized or over-watered; in heavy infestations of mealybugs, one may also notice sticky ‘honeydew’ excretions on the plant.
It seems that you do not have a heavy infestation of mealybugs on your plants–the easiest way to control (get rid of them) is to simply use “a cotton swab dipped in vegetable oil to dislodge and collect all the mealybugs you can find on your plants”. You may have to repeat this on a weekly basis until the plant seems to be free of mealybugs. Keep in mind that mealybugs tend to hide in areas where the leaf is connected to the stem (as in your photo).
For a heavier infestation, use an appropriate solution of an insecticidal soap (Safer’s) and spray the plant thoroughly in the affected areas. You may have to repeat the application after a few days. The best defense is to be vigilant–the sooner these mealybugs are detected and dealt with, the better.
Unless you have recently brought in another or new plant, it’s difficult to identify how the mealybugs have come into your condo.
You raise the issue of humidity–it’s worth thinking about–excess humidity can create an environment for mealybugs. Given the fact that we’ve had more overcast skies lately, the available light in your condo has been reduced (hopefully temporarily); this may have stressed your plants a bit which might make them more susceptible to pests. Perhaps you might reduce the amount of humidity in your condo for a while.
By dealing with the mealybugs as advised, we trust that your plants will continue to thrive.