The yucca or palm lily is true - which, by the way, is not a palm tree, but a species of agave! - as quite robust, but like any other living being, it can also become ill. Fungi are one of the most common pathogens on houseplants, with powdery mildew only very rarely appearing on the yucca. However, a very similar appearance is caused by a very specific pest.
The yucca palm is very rarely attacked by powdery mildew
Powdery mildew or gall mites?
Should your yucca actually develop mildew, the plaque can usually be removed quickly with a clean cloth and a little milky water. A mixture of whole milk and water helps against powdery mildew, although you should only use fresh milk - the bacteria it contains reliably kill the mildew spores. In the case of a severe infestation, however, only scissors can help in many cases, because these parts of the plant should be removed and disposed of immediately. But beware: A white, wipeable coating does not always indicate powdery mildew - gall mites can also be behind it. The gall mites found on yucca plants do not form galls, but instead sit individually on the leaves.
tips
Yucca plants often suffer from powdery mildew if the location is unsuitable.