Question
Hi,
I bought a yucca cane plant around 3 weeks back. Not only
have I been struggling with the correct amount of water for
it..but now I have started noticing black dots over some of
the leaves (both old and new as well as on the front and
under side of the leaves) These dots are very tiny, round
and probably a little smaller than the eye of a needle. I
started scraping them off the leaves and they come off
relatively easily. Is this some sort of plant disease?
Also a few of the bottom leaves are completely yellow and
wilted while a few leaves on the top have brown tips and
yellow halos. So now I am really confused as to whether this
is a case of over watering or under watering.
FYI I also spritz the leaves when I water the plant once a
week.
Please help me! Can you tell me what those black dots
are...and is my plant dying? I'm so upset as I don't want it
to die!

Answer
Hi Seena,

Small, slightly raised black spots that rub or scratch off easily are scale infects. True, they don't look at all like what we think of as insects, but they are. They are tiny sucking creatures that move when they are young, translucent and nearly invisible. As they mature, they produce a hard outer covering for protection and then they suck on foliage for nourishment.

The best way to treat these critters is to spray them with a solution of 5 parts water, 1 part rubbing alcohol and a squirt of liquid dish soap. The alcohol penetrates the outer covering and the soap helps spread the solution. The key is that you have to spray the entire plant - all leaf and stem surfaces - until they are dripping wet. If you miss a few of the immature ones, they will reproduce and in a  few months the infestation will be back. So do this outside or some location where you are not worried about the spray run-off. If you are really thorough, one treatment is usually adequate, but you should be vigilant in the future.

Plant pests are often a sign that a plant is under stress for other reasons. Pests love to prey on plants that are weakened. You have provided limited information abut how you are caring for your Yucca, but the symptoms certainly suggest soil that has not been allowed to dry out properly between waterings. That means the top quarter of the soil should be dry before you add any water.

If you repotted your new Yucca or it was repotted by the retailer just before your purchase, then that is probably contributing to the overwatering problem.

Yuccas come from dry regions so spritzing the leaves is unnecessary.

Finally, I should note that Yuccas need lots of bright light and must be within a couple of feet of a sunny window that is uncovered throughout the day. A Yucca without enough light is very easy to over water.

I have written an article on Yucca care that I will email for free to anyone who sends a request to me at my address below.

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