scale disease on torch cactus

Trouble shoot problems you are having with your cactus.
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splosh
Posts: 10
Joined: Wed Jul 03, 2019 12:04 am
Location: los angeles

scale disease on torch cactus

Post by splosh »

strange scale appearing on torch cactus. On some appears to be emanating from base of plant. On others, there is very bad scaring where flowers once were. Any idea what this is ? I've tried systemic fungicide over several weeks. Also Neem oil. No luck. Seems to be getting progressively worse. Any idea what this is, and to how to deal with it ?

Thanks.
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hegar
Posts: 4596
Joined: Mon Jan 23, 2006 4:04 am
Location: El Paso, Texas

Re: scale disease on torch cactus

Post by hegar »

Hello splosh,
I just noticed, that nobody did respond to your cactus problem.
In the topic headline you use the term "scale disease". There is indeed a disease, which is commonly called a "scab", but your cactus plant stems are not infected by it. I believe, that the problem is not caused by a pathogen. Thus a fungicide will not do any good. I have never used neem oil and do not even know, what kind of malaise it is used to cure. If it too is a pesticide employed to kill pathogens, it too would not work.

In my opinion, your plant is being attacked by an insect. It may be a mealybug, because those do have a whitish waxy covering of their body.
What I would do is the following:
1. carefully remove some of the unusual structures from your cactus and examine them under a hand lens with 10x magnification.
2. with a probe or needle move the specimen, so you can see both the dorsal (back) and the ventral (bottom) of it. If it is indeed an insect, you should be able to see tiny legs. Make sure not to puncture the specimen. Mealybugs are soft-bodied and will flatten, if their skin is pierced. Because you seem to have many of these "things" on your plant stems, it would not be a problem to destroy some of them, before you do get a good look at them.

You can see some of the afflictions affecting cacti when you go to the "Pests and Diseases" tab of CactiGuide.
Some plants within the cactus family (e.g. some Mammillaria spp.) do exude a white liquid, when they are injure. So, you may be looking at that also.

Perhaps by now you already did find out what you are dealing with and have found a remedy. I am sorry, that I did not respond sooner, but I believe, that you do deserve advice.

Harald
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