Mildew - regardless of whether it is real or false - is very rare on houseplants and therefore primarily affects yuccas that are cultivated outside in the summer or that remain in the garden all year round. However, a white, flour-like coating can also be an indication of gall mites, which are quite common in indoor yuccas.
How to control mildew on a yucca palm?
Mildew on a yucca palm can be effectively treated with a mixture of fresh milk and water. Use one part fresh whole milk and ten parts water to wipe off the infected leaves. If you have a gall mite infestation, rinse water (water with dishwashing liquid) is an effective alternative.
Fight mildew effectively
If it is actually powdery mildew, you can treat the leaves of the affected yucca with a mixture of whole milk and water. To do this, mix one part fresh whole milk with 10 parts water. It is essential to use fresh milk, as only this contains the necessary microorganisms that are effective against the fungus.
Identify and combat gall mites
On the other hand, these are gall mites - which, by the way, do not leave galls on yuccas! – then you can combat them effectively with dishwashing water. To do this, mix water and a few drops of dishwashing liquid (e.g. Pril, Fit) and wipe the leaves of the affected plant with it for several days in a row.
Tip
In the case of mildew, untreated milk is best: you may even have a dairy farmer near you who will sell you untreated milk. Supermarket milk is. Even if it says “fresh milk” on it, it’s always pasteurized.