Question
Our clinic received a yucca plant last fall as a gift. Sometime in late winter the plant began developing a tannish, "dusty" appearance to the leaves, which can be wiped off to some degree with a rag. Some of the leaves are turning brown and dry. This plant sits in a large southern-exposure window; in full, unobstructed sun. I do think we are watering after it goes dry enough. We have not checked the roots or tried to repot it; it is in a large plastic pot with a drainage hole, that sits in another, quite roomy, (decorative)plastic pot. I hope you can help; I have looked at other sites as well as other entries in this site and have not seen this problem described. Thanks, Claire

Answer
Hi Claire,

Yucca plants do often develop a light grayish film on their leaves as they oxidize. If that is what you see, it is not a cause for concern. Otherwise, I suspect your Yucca has spider mites, which look like tiny bits of dust and sometimes have a reddish or tannish tint. They are not common on Yuccas, but the high temperatures associated with the direct sun do create an environment conducive to spider mite reproduction.

I suggest that you mix a solution of 1 part isopropyl (rubbing) alcohol with 5 parts of water and a squirt of liquid dish soap. Use it to thoroughly wipe down all of the leaves - tops and bottoms - and then spray some liberally into the crevices where the leaves attach to the stems.

If lower leaves are turning brown and dry that is probably because the soil is getting too dry between waterings. Yuccas can do well in direct sun, but the soil should be kept more moist than usual in strong light. Water thoroughly as soon as the top half-inch of soil feels dry. Too little water can also contribute to spider mite infestations.

I have written articles on indoor plant pests and Yucca care that I will email for free to you (or anyone else) who emails a request to me at [email protected].

Please let me know if any of this is unclear or if you have any additional questions.

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Regards,
Will Creed, Interior Landscaper
Horticultural Help, NYC

Visit my website at: A link to PlantCareExperts.com