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Cactus/old man cactus has oozing black spot

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Expert: - 7/2/2010


Question

old man cactus
Hi, we have a fairly large old man cactus and noticed a black soft spot toward the top.  The spot seems to have gotten bigger and it is only in this place. Want to save the cactus if possible.

Answer
Dear John,

Unfortunately that is black rot.  Usually when you see it it's even more extensive inside the plant.  The only way  to save the plant is to get rid of all of it. So... get a very sharp knife and sterilize it with alcohol. Scoop out the rot until you get to clean tissue, white/green with no discoloration AT ALL.  Sterilize the knife with each new cut.  If you get rid of all of it brush it with a fungicide.  It will leave a hole that won't fill in, it will just callous  over.

Sometimes that treatment is successful. If there isn't enough healthy tissue left the only thing you can do is slice it off below the rot, again to clean tissue, then you'll have a flat topped
cactus.  Either way, if you do save the plant you'll need to repot it and throw the old soil away.

You're not going to know what you're dealing with till you dig in.

Good luck,

Maureen
    Questioner's Rating
    Rating(1-10)Knowledgeability = 10Clarity of Response = 10Politeness = 10
    CommentMaureen, Thank you so much!! We followed your instructions and repotted him and cut out the rotted area using the rubbing alcohol. I am happy to report a week later and it looks great, no rot has returned thus far and the hole we carved is dry and white inside. We really appreciate your input and knowledge. Have a great weekend.


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Maureen

Expertise

I can answer questions regarding the care and propagation of cactus and succulents and would actually group these together as folks often mistake one for the other and often their care is quite different. I also have a cold hardy cactus and succulent garden that has been quite successful. The subject in regard to classification of type is enormous and I wouldn't be able to answer all questions by any means. It is really IMPORTANT TO INCLUDE A PHOTO if at all possible and LET ME KNOW WHERE YOU ARE FROM, especially in terms of climate.

Experience

I have learned by reading books, by trial and error and by consulting with folks with much more knowledge. I have primarily grown C&S for the last 20 years.

Organizations
Cactus and Succulent Society of Massachusetts.

Education/Credentials
No formal training. See experience.

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