Disease to the enchanted castle

Trouble shoot problems you are having with your cactus.
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Freejon
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Disease to the enchanted castle

Post by Freejon »

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One piece of this venerable cactus seems to be suffering from the dark scaly disease at its tip and it is beginning to turn yellow. I am worried that the sickness will spread.

The plant as a whole has some black spots with cork-coloured edges. It is not widespread. From what I read that is probably a fungus. But is the damage in the other photo the same, or something else? And in either case, what should I be doing to take care of it?

All help much appreciated.

Thanks,
Jon
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Steve Johnson
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Location: Los Angeles, CA (Zone 10b)

Re: Disease to the enchanted castle

Post by Steve Johnson »

Hi Jon,

First of all, it would be helpful to know your geographical location so that we can give you advice based on where you live:

viewtopic.php?t=43819

The most serious problem is a fungal infection caused by the soil in your mix. I just posted a presentation on soilless mixes, so read this:

viewtopic.php?p=399084#p399084

Also, the pale green stems and that yellow stem indicate nutrient deficiency. Are you fertilizing the plant? If so, what's in your fert and how often are you applying it? Not sure how far you want to go, but you may want to pursue this:

viewtopic.php?t=47603

You're getting some good thorough information here -- once you go through everything in the links, let me know if you have any questions.
If you just want photos without all the blather, please visit my Flickr gallery.
My location: Los Angeles, CA (Zone 10b)
Freejon
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Re: Disease to the enchanted castle

Post by Freejon »

Thank you Steve.

I am in Salisbury, southern part of UK. Probably equivalent to US zone 7 or 8. The plant is on a windowsill that gets direct sunlight for about 5 hours in the middle part of the day. It doesn't normally get very hot though and doesn't experience temperatures below 10 degrees.

Last time I repotted I used a commercial cactus mix. Added some grit, if I recall correctly. I don't think I would want to go soilless. I have seen something about putting liquid copper in to the watering as an anti-fungal soil treatment. Is that a good option?

If it is in the soil, is there any point in topical treatment, and if so, what would you suggest? I have Neem oil that I use on another plant and I have an antibacterial solution that is 80% ethanol if either are useful, but would get anything else that is necessary, of course.

I have not been fertilising since the re-pot, because I thought the fresh soil would have good nutrition. I am impressed by your analysis of fertiliser requirements, but also overwhelmed. This is an old and generally healthy plant which has been in my care for about 4 years, prior to which I think it had only been watered. I have some scientific training, but your formula feels like more than I can engage with. I took on board your comments about micronutrients though. Does the product below look OK?

Best wishes,
Jon

Contents

EC fertilizer

nitrogen (N) - 5%

phosphorus (P2O5) - 4%

potassium (K2O) - 9%

Micronutrients:

boron (B) 0.02%, copper (Cu) * 0.002%, iron (Fe) * 0.02%, manganese (Mn) * 0.015%, molybdenum (Mo) 0.002%, zinc (Zn) * 0.015%

* chelated by EDTA
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Steve Johnson
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Re: Disease to the enchanted castle

Post by Steve Johnson »

Hi Jon,

If you don't want to go soilless, you should probably lean out the mix with more grit. My default recommendation -- 50% grit and 50% soil, although you may want to go a bit leaner. Unfortunately I can't give you any recommendations on an anti-fungal treatment because I don't experience problems with fungal infections. Topical treatments are useless, so IMO the best thing to do would be to cut off the diseased stem well below the yellow part and dust the exposed surface of the cut with sulfur powder. Since the diseased stem is on top of the plant, catching this now is a good time to do it before the fungal infection spreads down.

Looking at your fertilizer:

N - 5%
P2O5 - 4% x .436 = 1.744% elemental P
K2O - 9% x .83 = 7.47% elemental K

That's a really good NPK balance, and the micronutrient profile is good too. I don't see a mention of Calcium or Magnesium, though. While N, P, and K are the primary major nutrients, Ca and Mg are in fact secondary major nutrients. If your fert doesn't include them, I highly recommend adding a Nitrogen-free CalMag supplement to your plant's feeding regimen. Also, cacti should be fertilized only when they're in growth during spring and summer.
If you just want photos without all the blather, please visit my Flickr gallery.
My location: Los Angeles, CA (Zone 10b)
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ohugal
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Re: Disease to the enchanted castle

Post by ohugal »

The yellowing of the cactus seems to be orientated on the side of the window. Is that correct? I see a bit of yellow at the base of the plant, but I assume that's corking?
I agree with Steve on the topical treatment.
Be carefull with applying Neem oil on a cactus. It creates an oily layer on the plant which takes a lot of time to break down and can cause phototoxicity. The ethanol antibacterial spray you mentioned, is it a product specific for plants?
When did you say you repotted?
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temperate, maritime climate with mild winters and cool summers
hardiness zone 8a
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Steve Johnson
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Re: Disease to the enchanted castle

Post by Steve Johnson »

ohugal wrote: Thu Feb 09, 2023 6:38 amI see a bit of yellow at the base of the plant, but I assume that's corking?
Actually, there are a bunch of pale green stems in that photo, and another bunch of yellowish stems facing the window. A direct sun exposure problem? Nope, I think it's just a coincidence. Jon, what I see is nutrient deficiency that needs to be addressed with a regular fertilizer regimen in the spring and summer. Assuming that it's a liquid fert, I'd normally recommend dilution of 1.3 mL per liter of water, but you wouldn't go wrong if you up it a little bit by diluting 1.5 mL/L. The soil in your mix helps to retain any fert not taken up by the plant. You should be fine by fertilizing with every 3rd watering as the waterings in between release residual nutrients to the plant.
If you just want photos without all the blather, please visit my Flickr gallery.
My location: Los Angeles, CA (Zone 10b)
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ohugal
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Re: Disease to the enchanted castle

Post by ohugal »

I’m curious when it was last repotted. Under normal growing conditions and with no fertilizer, how long would it take to develop such yellowing? Also, what type of deficiency could it be?
Location
Antwerp, Belgium
temperate, maritime climate with mild winters and cool summers
hardiness zone 8a
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Steve Johnson
Posts: 4514
Joined: Thu Nov 03, 2011 4:44 am
Location: Los Angeles, CA (Zone 10b)

Re: Disease to the enchanted castle

Post by Steve Johnson »

ohugal wrote: Thu Feb 09, 2023 12:24 pm I’m curious when it was last repotted. Under normal growing conditions and with no fertilizer, how long would it take to develop such yellowing? Also, what type of deficiency could it be?
Pale green/yellowish skin indicates Sulfur deficiency. Hard to tell how long it took for that to show up, but the deficiency isn't too bad yet.

Jon -- if your fertilizer contains only a small amount of S or no S at all, a little bit of Epsom salt in the mix will reverse the S deficiency. Unfortunately I can't advise you on how much to put in, but the goods news is that S toxicity in cacti is incredibly rare.
If you just want photos without all the blather, please visit my Flickr gallery.
My location: Los Angeles, CA (Zone 10b)
Freejon
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Re: Disease to the enchanted castle

Post by Freejon »

Thanks, both.

Repotting took place about 18 months ago. The serious yellowing is only to that single stem and to me looks to relate quite specifically to the scabbing. It is central and at the top, so it does get whatever sun is going. There are many stems both bigger and smaller and many of which face the window that are not affected and look a healthy green colour.

There are many smaller stems on one side that are less green, but not scabbed / spotted and not yellow. That side gets less sun and I had thought that to be a cause but I am interested to see if it responds to feeding. Winter is almost over, so I can find out soon :-) .
Freejon
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Joined: Tue Feb 07, 2023 11:40 am

Re: Disease to the enchanted castle

Post by Freejon »

I have found neem oil directly applied to the infection is effective. Ethanol is too, but not as strongly.

Will wait and see whether feeding prevents a recurrence
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