It looks like powdery mildew. Neem oil might do the trick, and there are other fungicides I haven't used myself. Improving the air circulation in the plant's vicinity will give it less interest in growing there.
-perL

Thanks! I will apply the neem oil treatment. If it doesn't help then I will have to move it.

You're welcome... I phrased that badly about air circulation, but you obviously were able to see past it and read my mind, lol. I meant to say that good air circulation discourages the powdery mildew and other fungal plant diseases. Hope the Neem helps. I just used it on some annual verbena outside, but missed the lower leaves.... gotta try again. I like neem because it discourages fungal stuff and bugs and is less toxic than many other remedies marketed for plants. That's a good looking plant. Enjoy. -perL

I just read that powdery mildew is made worse by wide temperature swings, in particular hot days and cool nights. Also, as already suggested, better air circulation and spraying with neem or a fungicide should help, but you will probably have to spray periodically.

We had mildew on some Begonias at work recently, and one of the co-workers suggested misting the leaves with a solution of baking soda. It did work, kinda, but since we didn't change the conditions they were growing in (no room to move them or spread them out), it came back.

It was recently transplanted? what kind of care doe it get?

I changed the pot about 6 months ago. This is the second one. The first one I over watered it so I was careful not to do this one but now this. Maybe it time to let this one go too. I was told they thrive on neglect so I though; my kind of plant

They do thrive on neglect but needing the right lighting. South/west facing bright direct light. If you can put it outside I would do that asap.

well I could put it on the back enclosed porch that have good light but I am concerned about it being 35 to 37 degree outside. Is that to cold?

oh yeah too cold. You might just have to wait it out until it warms up and see how it looks then.

nichjan, I have the exact same problem as you with my yuccas. I have scoured the internet for answers and even asked my local nursery guy and he thought it might be mealy bugs or mites. I thought it was some kind of fungus, but he didn't agree. I've still had a hard time trying to find something that will kill those, though, and I'm still not sure thats what it is. It is EXACTLY like what you have pictured.

still alive?

I have the same problem too. I’m convinced it’s powdery mildew and not spider mites. I’ve had spider mites on other plants in the past and it does not look like this at all. I still haven’t managed to fix it though.

Any updates here?

HU-455855763, we'd need an extreme closeup of that.

I have a similar problem. Is there an update on this? :) Thanks.

Andre, that definitely looks fungal. Is the tip still alive?

Is there good drainage in the pot? Too much moisture makes this worse.

If there are any good leaves left, I'd prune off the sick ones- they'll cause more infection.

If that trunk is still good and firm, it will sprout more once the problem is corrected. For killing the fungus, neem oil is a good choice. Mist the plant with it outside or in the shower if you can, so the spray doesn't get everywhere. Neem is a bit smelly, but good because it's not so toxic. It also can be used as an insecticide.

I see I mentioned neem before. I am sorry for being repetitive, but I do like the stuff.