Question
I have a large Yucca and three small ones that has been thriving for many years.  Recently the smaller ones have begun to yellow and are covered by a white powdery substance.  Do you know what it is and what I can do about it?


Answer
Cat,

Sounds like your yuccas have powdery mildew. Spray the plants daily with Lysol Spray or the generic version, making sure that you get the tops and bottoms of all leaves. Do it daily for a week then every other day for another week, then twice a week for 2 weeks, then watch it for anymore signs of the powdery mildew. If you see signs of it again go back to daily sprays or every other day. To prevent this in the future be very careful about not overwatering it and put a fan on the plant for greater air circulation to prevent powdery mildew.
Good luck!

Darlene