Purple and orange spots on ferocactus

[Steve Johnson]

They should, although not until the roots are growing again. Estimate a month or two to see the spots clearing up.

[greenknight]

I've had good success with a soapy water soak, should be fine.

I expect the purple will fade. Orange spots may remain, but they'll be hidden underneath as it grows.

[ohugal]

I recently read on the BCSS forum someone submerged a Lithops with root mealies in methylated spirits. I have done it as well on some Pterocacti recently without any side effects. I don’t know a more specific term for it. It’s also sold as fuel for ‘stoves’. Here, it also has a blue tint to it. It can also be combined with soap to make a mealy bug spray. After using it, I sieve it with a very very fine mesh in order to re-use it. The hot bath is also effective but the temperature has to be constant and I would only use it on cacti. Succulents in general don’t respond well to it.

[greenknight]

I recently read on the BCSS forum someone submerged a Lithops with root mealies in methylated spirits. I have done it as well on some Pterocacti recently without any side effects. I don’t know a more specific term for it. It’s also sold as fuel for ‘stoves’. Here, it also has a blue tint to it.

Sold as "Denatured alcohol" in the US, it's ethanol with methanol and maybe other additives such as bittering agents to make it undrinkable. The blue tint is dye added to identify it. Works the same as IPA for pest control.

[Ilvin]

Oh yeah, I've used alcohol on above ground mealybugs to good effect, I wasn't sure it was a good idea to spray it on the roots.

Anyway, a week in and the cactus spots haven't got worse so I'm hoping I got them all. I'll keep a watch out for the purple fading.

[Ilvin]

Hello everyone, this problem has unfortunately got worse. It had stalled for a month or so and I was expecting summer to fix the issue if its fungal. That doesn't seem to have happened.

More spots are appearing, mostly towards the base of the cactus, usually around the spines. They always start off purple, then go orange (The few that have healed after going orange have got a normal corked colour). I can post pictures of the new spots tomorrow but they are the same as the original spots.

I fear the root mealybug was because the plant was weakened by whatever this issue is, not the other way around. The cactus is taking up water, but also starting to look wrinkled, and it got significantly more spots after some hot weather this past week. Could heat stress be an issue? Even with a desert cactus?

Or could this be fungal? If it is, how do I treat it? I've heard a some kind of copper solution can be used as a fungicide (potentially copper sulfate?), would this be appropriate to a cactus? If I don't do anything now I suspect the cactus is headed for a slow death.

[Steve Johnson]

I've been going through your thread, and there's a question I didn't ask which I'll ask now -- are you keeping your cacti indoors year-round?

[Ilvin]

Not this cactus, its outside all summer although I bring it in most of winter to avoid rain.

Its outside in full sun now, I actually moved it to get more sun this year, and its quite windy here so it has plenty of air movement.

[Steve Johnson]

Not this cactus, its outside all summer although I bring it in most of winter to avoid rain.

Its outside in full sun now, I actually moved it to get more sun this year, and its quite windy here so it has plenty of air movement.

Okay, if sunlight and ventilation are good, and you knocked out the root mealy infestation, what about your fertilizer? If you can provide me with the guaranteed analysis on its label, we'll see if that could be the problem.

[Ilvin]

Sure, I'll attach a picture of the analysis, but from my basic research I think its ok. Or at the very least unlikely to be bad enough to be the cause of this.

20240205_180536.jpg (59.79 KiB) Viewed 1750 times

In any case, I've damaged the cactus further. I sprayed it with isopropyl alcohol yesterday evening in the hope that it might slow the issue while I figure out a better treatment. I've used this before, even on this cactus, with no issues. Today, however the poor cactus has bleached skin.

As well as that, I've attached pictures of the purple spots, notably the purple patches at the bottom that are larger and new this past week.

20240205_175204.jpg (147.04 KiB) Viewed 1750 times

20240205_175215.jpg (88.08 KiB) Viewed 1750 times

20240205_175530.jpg (125.66 KiB) Viewed 1750 times

20240205_175539.jpg (123.5 KiB) Viewed 1750 times

I suppose treating it at night was where I went wrong. I really hope I haven't killed it myself.

[Steve Johnson]

We'll go through a process of elimination here:

• Lighting and ventilation -- no problems.

• Root mealy infestation -- gone.

• Fertilizer:
  

  

  20240205_180536.jpg (58.15 KiB) Viewed 1725 times

  Believe it or not, P is a little lower than I'd want, but I think the amount in your fertilizer is acceptable. K higher than N -- good. Calcium is an important secondary major nutrient and the fert doesn't have it. Dash in some limestone or gypsum granules as a slow-release form of Ca. Unfortunately I don't know the genus, so find out if your Ferocactus species is native to limestone soils. If you're not sure, you won't go wrong with gypsum.

Another source of Ca and Mg can be found by acidifying tap water. However, the acidification procedures are a bit complicated, and I don't know if you'd be willing to go that far. If you'd rather not, water your cacti with distilled water, R/O water, or rainwater.

One last part of the elimination process -- your potting medium:

One more thing, Ferrocacti seem to like a rather poor soil. That is - mainly mineral. Yours looks a bit too rich in organics.

Completely agree. Looking at Ilvin's photos, it appears that the organic material is chipped/composted tree bark of some sort.

When I investigated various soilless mixes, chipped tree bark held out a lot of promise as the organic component to go with the mineral component. Then I came to find out that tree bark eventually becomes hydrophobic after repeated watering and drying out cycles. In the absence of a suitable organic material that isn't hydrophobic, I now believe that soilless mixes work only if they're pure mineral gravels.

Unless you recently changed to a different mix, I have a feeling that your problem comes from the tree bark in the mix I saw in your very first photo. If you're still using the same mix, I see 3 alternative options for you:

• Straight pumice or calcined clay granules (AKA Leca balls) -- IMO okay if you live in a dry climate. Both minerals hold a surprising amount of water.

• A mix of pumice or calcined clay and granite gravel. The problem with straight pumice/calcined clay in a fairly humid climate is that it takes too long to dry out. Granite in the mix acts as a sort of "moderator" allowing the pumice/calcined clay to dry out in an appropriate amount of time. I use a mix of 60% pumice and 40% granite gravel -- works well in my coastal Mediterranean climate.

• A mix of pumice or calcined clay and soil -- 60% mineral/40% soil or 70% mineral/30% soil depending on the humidity in your local climate.

Options 1 and 2 have close to zero cation exchange capacity, so you'd have to fertilize every time you water in the growing season. My cacti get all the Ca and Mg they need from acidified tap water and the fertilizers I use, so the zero-CEC problem is solved by fertilizing every time I water. In your case, limestone or gypsum probably won't work without a decent amount of CEC in the mix -- and that'll be provided by a soil component.

I sprayed it with isopropyl alcohol yesterday evening in the hope that it might slow the issue while I figure out a better treatment. I've used this before, even on this cactus, with no issues. Today, however the poor cactus has bleached skin.

Cacti with waxy skins are damaged by alcohol sprays, so I think that's what happened. Not life-threatening unless you do it too often.

By the way, those purple spots don't look like a fungal infection. Examples of what they look like:

fungus_epi.jpg (45.54 KiB) Viewed 1725 times

The red circles point out fruiting bodies in the dried patches. If you do encounter a fungal infection, you'll know what to look for.

[Ilvin]

I tend to water with 50% rainwater 50% tap, because my tap water is hard. The pH is likely still a little on the high side, but that hasn't changed in the two years I've had the cactus without this problem. I guess its still possible its low on calcium, so I might add some.

I re-potted it in fresh soil mix when I took care of the mealys. I went for a 50% soil/50% inorganic (gravel/perlite) and did make an effort to remove the bits of bark from the cactus and succulent soil I buy - but I can still see some on the top of the mix so clearly I didn't get them all.

Honestly I have no idea what the issue is, I thought it had gone away or at least was resolving until the past few weeks. I might attempt to re-treat for mealys just in case, but its not really the season for it - supposedly they like humidity. If this is a sign of plant stress, could high temperatures cause it if the plant was only just recovering from the mealybugs? I ask because it was very hot last week and this is the cactus' first summer in full sun.

[MikeInOz]

The whitish discoloration is sunburn. It might recover. Place the plant in a situation under an open tree canopy where it get strong but chequered light
- if you can. Purple in plants is produced under stress as a protective response. It might be from high temps, sudden high light or cold temps. It does not look too bad to me.

[Ilvin]

Hi Mike, it does look like pictures I've seen of sunburn but I'm fairly sure the isopropyl alcohol did that. Its on the exact area where I sprayed it.

The consensus does seem to be its not fungal, which is good, but I do wish I knew what was upsetting the poor cactus. It certainly looks worse now after the isopropyl alcohol, which is annoying. Its not gone soft in those areas but it does look like its scarring.

[Steve Johnson]

I think there are a few things you can do to improve the situation...

I re-potted it in fresh soil mix when I took care of the mealys. I went for a 50% soil/50% inorganic (gravel/perlite) and did make an effort to remove the bits of bark from the cactus and succulent soil I buy...

I'd go a bit leaner, maybe 60% mineral/40% soil or 70% mineral/30% soil. Mike knows Australia's various climates whereas I don't -- Mike, what would your best mix recommendation be for Ilvin based on his local climate in Perth?

Your fertilizer appears to be good. Is it slow-release, water soluble granules, or a liquid concentrate? If it's a slow-release fert, how much are you adding to your pots? If it's water-soluble, knowing the nutrient dosages and frequency of application will be important -- give me the details on dilution rate and how often you fertilize. By the way -- given the problem with tree bark being hydrophobic over time, I have to wonder if your cacti were being slowly starved of nutrients in that mix. CEC of the soil in your new mix will improve the nutrient situation quite a bit. I believe you have 6-8 weeks of growing season left in Australia, and while you can't expect miracles right off the bat, you may see improvements in the way your cacti respond to your fert in the new mix before your growing season ends. Your answers to the questions I just asked should be helpful.

Regarding the important roles of calcium and magnesium to plant health, this article on hydrobuilder.com (https://hydrobuilder.com/learn/npk-rati ... t-balance/) explains it well:

• "Magnesium and calcium go hand in hand, and are often an area where plants become deficient. Magnesium helps aid in the uptake and utilization of other nutrients, along with producing carbs and sugars to help during flower."

• "Calcium has a similar role in plants as in humans, helping produce strong cells and root walls. This leads to stronger plants. We've recently come to understand that calcium is actually the dominant nutrient in most plants." [My emphasis]

Quite a revelation, and it backs up a couple of things Mike has said in previous posts -- "there's no such thing as too much Ca" and "there's no such thing as Ca toxicity". In fact, I offer the possibility that Ca higher than N could be a very good thing at least for cacti and succulents. I also see a couple of positive implications for cacti getting plenty of Ca:

• Strong cell walls in the stem make it more difficult for sucking pests (mealies, armored scale, and pest mites) to get a "toehold" on the skin.

• Strong root walls discourage or prevent root mealy infestations.

These are just theories -- given Mike's long experience with cacti and succulents, it'll be interesting to find out if he says they're actual facts. Regardless of whether they are or not, I'm highly confident that you'll need to give your cacti substantially more Ca.