Rot in M. geometrizans

Trouble shoot problems you are having with your cactus.
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pokie
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Location: Portland, OR

Rot in M. geometrizans

Post by pokie »

Hello,
I have a large cactus that suddenly developed rot in a large branch. It looked fine 4 days ago and now the branch is completely gone. I have sawn it off at the trunk and checked for rot at the cut. The cactus has been in a south facing sunroom for the last 6 months. I water it deeply once a week. Substrate is mixed potting soil, pumice and loose rock.

Is there anything I can do to help the plant recover and/or avoid this problem in the future?

Photo album: https://imgur.com/a/qCvLw6g
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

Another part of the cactus is rotting again. I don't know what to do to stop this.
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

I updated the album in the 1st post with more photos and comments.
A_G_R
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Re: Rot in M. geometrizans

Post by A_G_R »

It does not look healthy after your last cut, you shouldn't see any brown tissue on the cut.
I think you are over watering, is the soil drying in between waerings?
Alejandro
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

The substrate is fairly porous. I am reasonably confident it's drying out properly. I dug through the top inch of the soil today, and it's bone dry even though I watered 2 days ago. I have had the plant for 5 years, so it could be that moving 600 miles north changed the climate enough that I didn't adjust well for it. I used to water it every day in the summer in CA heat (frequent 100+F temperature), and now water once a week. My general practice is to water my plants thoroughly and have a well draining enough substrate to avoid excessive water accumulation.

That said I am considering digging it up, examining the roots for potential root rot issues and repotting it. I am worried whether this would stress out the plant too much given all the hacking I did today.
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

As for the brown tissue, the circular orange-ish bit in the center is wood-hard. I don't believe it's rot. I suppose I can cut the already removed top section further to see if it disappears.
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

Yeah, in the second to last photo you can see a cut that's along the length of the trunk on the pieces on the right side, and the fibers of the orange part are fairly clearly visible. I am fairly confident it's bark-like tissue of some kind and not the yellow-brown rot. I also think that if I am wrong and it's problematic, then the whole plant is forfeit, based on the first limb I had to cut off in July since there was a lot of the orange hard stuff at the base of the trunk.
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

I dug up and repotted the plant in fresh soil (equal parts granite, pumice and fir bark with a dash of compost). It was mostly dry with some mild dampness deeper in. I should probably water less often. I took some photos of the roots.
https://imgur.com/a/Xbu6PGa
The roots looked ok to me.

I also kept all the chunks I cutoff. The old top of the trunk looks healthy, and I will replant it later. But all 3 middle sections grew green mold after 3 days. I am hoping this confirms my hypothesis about the different colors in the cuts.

I am also considering getting a small fan for the sunroom to help with circulation.
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ohugal
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Re: Rot in M. geometrizans

Post by ohugal »

It is indeed important when you make a cut to remove rot, you cut back to entirely healthy tissue. Disinfect your cutting tool after each cut. If I were you I would take my time and poke with a pencil or small stick each part of the cactus which you suspect is infected. If it's mushy, it's rotten. You could apply aluminum, charcoal or sulphur powder to the cuts. If you think there is mould growth, even superficially, perhaps apply a fungicide to get rid of it. The type of fungicide depends a bit on what you have acces to. Good luck! I think all of us went through such a process. It can be very stressfull, but cacti are resilient and it is very rewarding when a sick cactus gets back on top. Even when they don't look as their old selves.
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Antwerp, Belgium
temperate, maritime climate with mild winters and cool summers
south-west facing window in a city appartment
min. winter temp. 16°C/60.8°F
no outdoor or winter rest capability
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

I didn't think to disinfect between every cut, hmmm. I treated the cuts with hydrogen peroxide - another site indicated that would work for this purpose. I did check the cactus thoroughly for softness and even cut off a small healthy bit to look at the tissue inside for reference. Fungicide is a good idea, but I am not sure what type of delivery method is safe indoors.
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

I found some neem oil-based fungicide in my supplies, but I am not sure if that's sufficient.
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greenknight
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Re: Rot in M. geometrizans

Post by greenknight »

Neem oi, lik most fungicides, is a preventative, stops fungus spores from growing. It won't cure an established infection.
Spence :mrgreen:
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

What sorts of things can I try instead?
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greenknight
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Re: Rot in M. geometrizans

Post by greenknight »

Cutting off the rot is really the only cure. If the disease organism has spread too far though the plants vascular system, it may not be possible to save it. Tissue doesn't have to be rotten to be infected, this is why you're advised to cut off anything that's discolored. Keep cutting off any infected part, and hope.

Moving from California to Portland is a fairly big change, on top of that it's been a bad year for cacti - cool, damp weather persisted late into the spring, and since then it's been more humid than usual. I winter my cacti indoors and move them outside in the spring - did that later than usual this year, and I held off giving them a full watering until the weather warmed up. I mostly avoided rot problems, but I may have overdone it - some branches on my Mammillaria elongatas dried up completely, the little dribble of water I gave them was apparently not enough. At least they survived! The only cacti I lost to rot were two Ferocactus fordii seedlings that immediately turned to mush when I finally gave them a good soaking. Those seem to be difficult in this climate - I planted 20 seeds that all came up, 12 survivors were transplanted, and there are three left alive. They're in their 4th year now, hoping that they're tougher when they're out of the seedling stage.

It's a shame to lose a big old cactus like that, but sometimes it can't be helped. At least you have cuttings, eventually could grow another nice big one. Practice strict sanitation with the cutting(s), keep well isolated from the infected old plant. Adjust your watering schedule to the weather, delay watering when it's damp and cloudy - and good luck.
Spence :mrgreen:
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pokie
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Re: Rot in M. geometrizans

Post by pokie »

Thanks for the info.

I am just keeping all my plants indoors and installing a huge fancy light soon. If/when I overcome the pest problems I am hoping it will keep them easier to deal with. I suppose I should invest in a dehumidifier given our climate.

I still have hope the vascular system is fine, but we'll see.
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