Diseased cacti. What is it? How to treat/prevent?

Matt G(z11 HI)October 24, 2011

Here is possibly the worst case of this disease I have seen in my plants (on Echinopsis subdenudata). Many of my cactus plants have been getting this disease.

Some susceptible cacti: Leuchtenbergia principis, Rebtia heliosa, Echinocereus viridiflorus

Some resistant cacti: Astrophytum spp., Echinocactus, Parodia spp.

My Hoodia plants are also having similar symptoms. Most of my plants just get small brown spots all over. It seems to somewhat be from growing conditions, since some of my Echinopsis plants in other areas of my garden have symptoms only visible upon close inspection (not a problem to me). Has anyone seen this before and know what it is? It is my speculation that this is a fungal or bacterial disease.

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I think your cacti is being attacked by spider mites. I only know two options to treat it (there may be more): Increase the humidity or introduce a mite that eats the spider mite.
I might be wrong though.

    Bookmark   October 24, 2011 at 1:29PM
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bikerdoc5968 Z6 SE MI

If it is spider mite, you should be able to see them with a magnifying glass as they are VERY tiny. And if it is an infestation of mites, Bayer Advanced 3-in-1 Insect, Didease & Mite Control or any insecticide containing Imidacloprid (Merit) will do the trick. Find it at any of the big box stores.

    Bookmark   October 24, 2011 at 3:15PM
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Matt G(z11 HI)

Thnks for the replies. I do use imidicloprid on my plants, but mainly for mealybugs and ants. Not all my plants have been treated and I haven't tried to observe any differences between plants that have been treated and those that haven't. Now that you both have mentioned mites I will do a closer examination. Are the mites you refer to the same spider mites that cause yellowish/copper speckling on broadleaf plants (red, brown, and two spotted spider mites)? I don't seem to have a spider mite problem on any of my susceptible non-cacti plants but I do have broadleaf mite damage on highly susceptible plants.

    Bookmark   October 24, 2011 at 6:55PM
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Looks like mites, yeah. You could try washing the plant off to. They're not that strongly attached. Spraying it with neem or something could work.

Probably not fatal. I had this happen on one of the (few) surviving cactus I had and it just started branching/offsetting -- essentially what yours is doing.

That reminds me. I also use Imidacloprid to treat mealies. I heard it wasn't toxic to mammals unless ingested and in fairly large quantities. Since my plants are inside right now (Yay complete lack of fall, straight to winter!), should I worry about trace amounts of it getting on my carpet/clothes when I water things?

    Bookmark   October 24, 2011 at 7:53PM
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Imidacloprid is an insecticide with a very specific neurotoxin in it that only kills insects. Using this on something that has spider mites is NOT recommended as it only will kill everything BUT the spider mites (mites are not insects), and can often make a case of spider mites worse, as mites often have natural predators (some insects) which you will have killed off with the Imidacloprid. I cannot say what is damaging your cactus's exterior is spider mites, but if it is, pick just about anything else BUT Imidacloprid. Same goes for treating aloe mite (will NOT kill Aloe mite either, as it is a mite, not an insect).

This is the same product that is in Advantage, the flea product you put on dogs and cats. Yes it is extremely safe for dogs and cats, but if your cat or dog has ear mites or scabies, it will not help at all as those are also mites, not insects. Same situation.

Use a mite killer or some broad spectrum plant pest toxin if you want to kill mites on your plants. Note: some products containing Imidacloprid will ALSO have something that kills other invertebrates (like mites, spiders, scorpions, centipedes, snails etc.). A combo product might work OK for spider mites.

    Bookmark   October 24, 2011 at 9:31PM
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I've never actually had an issue with spider mites being really persistent. As I said, I usually just hose them off on the rare occasion some do show up, and I don't get much of a recurrence. On the other hand I have a TON of issues with mealies. I wonder if it's a regional thing.

    Bookmark   October 24, 2011 at 10:10PM
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