Cactus rot or disease??

tashr324July 13, 2008

Hi - My cactus recently dropped off a couple of lobes, and upon inspection, I realized that some of sections were covered in what looks like a layer of sand. This happened fairly quickly, maybe less than a week? I rarely water this cactus, but it has been extremely humid here lately. The cactus is kept indoors, in a bright window (south facing). In one of the pictures, you can see where a piece has broken off. Any idea what this could be, if the plant can be saved, or if I should be concerned for the other plants in its vicinity? Thanks!


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Although a little difficult to be sure from the photo, it looks like a major infestation of mealy bugs. That "sandy" coating is in all likelihood, hundreds and hundreds of little insects bleeding your plant dry. You can try running a fingernail across one, and if it squishes and leaves a slimy, greenish streak, it's mealies. With the stress of the infestation, it looks as though it is now rotting, causing pads to fall off and the brownish splotches.

Unless you have some major sentimental attachment to this plant, it probably isn't worth trying to save. It will be scarred and weak, even if you somehow manage to get rid of all the mealies. Worse, it is posing a serious threat to your other plants. In fact, you should carefully inspect all of them, including their roots, to make sure they aren't infested already. Sadly, it looks like this one is destined to end up in the trash...

    Bookmark   July 14, 2008 at 5:21PM
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I strongly disagree about this being mealy bugs. I have had mealy bugs in my cacti on occasion, and they always present themselves with white clumps of cottony, sticky fluff, not a "sandy" coating as Tasha describes. In my opinion it is most likely a humidity or overwatering issue; it appears some rot has already set in. Personally, I would cut off a 3 or 3 of the newer, less affected pads, let the cut heal for a week or so, then repot in a clay pot with a dry cactus mix with good drainage. The rest I would probably discard.

    Bookmark   July 14, 2008 at 6:50PM
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"Mealy bugs" is a pretty broad term that refers to a large family of scale insects. Some produce more of the powdery wax than others and even for a given species, different conditions can yield different amounts of the waxy build up. Just because they don't look like *your* mealy bugs doesn't necessarily mean they aren't still mealies. Anyway, like I said, none of us can be sure of exactly what the problem is from those photos. However, over watering or too much humidity absolutely can't be the singular cause of any "sandy" deposits on the pads.

    Bookmark   July 14, 2008 at 7:56PM
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Hi - thank you both for your responses! I did do the "fingernail test" and got no green slime. In fact, it was just kind of gritty and dry. But I poked around a bit and there is quite a bit of rot, unfortunately. So, I may take Christopher's advice to try to save a healthier looking pad, but most of it is going in the trash. I already put it outside just to get it away from other houseplants, and so far the others don't seem to be affected. I'll have to check out their roots tomorrow. Thanks again to both of you!

    Bookmark   July 14, 2008 at 10:43PM
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Tasha, good luck with your cutting or cuttings.

Sorry, joscience, but every case of mealybugs I have come across on cactus and succulents over the past 3 decades or so has always presented the same, with clumps of white fluff. Of course, other types of scale are different; brown scale for instance.


    Bookmark   July 15, 2008 at 10:44PM
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