Purple and orange spots on ferocactus

[jerrytheplater]

Hi Mike

I remember you saying about the "seasoning" before. Its fall here now. Straight K2SO4 at what concentration K? How much Calcium in ppm?

Hi Jerry
K2SO4 at 1 gram/Lt would be considered ''full strength'' so it would depend on how much you water between applications. If you are drying things off, one application at full strength should be acceptable or 2 applications at 0.5 grams/Lt with watering in between. No other fertilizers after that.
The Calcium should be included in the mix as gypsum or limestone or both. Applied as a liquid you would end up giving N as well. (CaNO3) Calcium chloride is a possibility but I don't like to use it.

Thanks Mike. My cactus are all under cover now as we are having a rainy week. They will need one more water. 1 gm/liter

[Steve Johnson]

Hi Mike

I remember you saying about the "seasoning" before. Its fall here now. Straight K2SO4 at what concentration K? How much Calcium in ppm?

Hi Jerry
K2SO4 at 1 gram/Lt would be considered ''full strength'' so it would depend on how much you water between applications. If you are drying things off, one application at full strength should be acceptable or 2 applications at 0.5 grams/Lt with watering in between. No other fertilizers after that.
The Calcium should be included in the mix as gypsum or limestone or both. Applied as a liquid you would end up giving N as well. (CaNO3) Calcium chloride is a possibility but I don't like to use it.

Not true if the grower is using a nitrogen-free CalMag like this:

https://www.amazon.com/True-Organic-Pla ... 9hdGY&th=1

Mike -- even though my cacti are getting Ca and Mg from acidified tap water, is adding 1/4 tsp. per gallon of the TPS CalMag okay, or could I bump it up to 1/2 tsp. per gallon for their last deep watering of the year this coming weekend?

[Ilvin]

Hi Steve, thanks for the detailed information. I'm aware my mix for the ferocactus is a little on the organic side. There is more perlite lower down, but I hate the stuff in the top layer because it floats (sadly I've been unable to get hold of pumice as an alternative). That said, I do intend to repot with less organics at some point in the near future.

Getting into pH, I don't have a pH meter currently, although I used to have a cheap testing kit hence why I'm aware of the approximate water pH. Why don't you think 50/50 rain water/tap water is a good idea? The rain should be fairly neutral (although I suppose that'll depend on my tank and I haven't tested it), and the tap water is certainly alkaline, as I've said.
I suspect the amount of calcium in the water here is higher than any plant could actually want. I cannot stress enough how obvious it is that the tap water is hard when I boil water. Honestly I have been diluting less because of pH and more because I was concerned about a gradual build up of minerals like calcium in the soil.

What I don't know is how critical pH is to plant health - now I know that either too acidic or too alkaline will be very bad for the plant, but there's bound to be a safe range. Do ferocacti tolerate a large range? pH of 5.5 that I've seen here seems surprisingly low. Surely directly using limestone to add calcium would raise the pH higher than that, and that seems to be an accepted source.
What sort of plant stress would I see if I have the pH wrong, given that I currently do not have a pH meter?

[Steve Johnson]

Hi Ilvin,

First we'll go through the pros and cons of rainwater and tap water:

Rainwater

• Pro -- the water doesn't contain the calcium bicarbonate you'll get from tap water. When tap water evaporates, calcium carbonate is left in the pot. If you see a nasty-looking white buildup on the outside of a porous clay pot, that'll be insoluble calcium carbonate which makes Ca unavailable to plants. When it builds up in the pot over a long period of time, the roots will eventually suffer. You won't have this problem with rainwater.

• Con -- plants under pot cultivation need to get their calcium in some way. Ferocactus is a limestone grower, so you can add a little bit of limestone in your mix. You can do the same with other limestone-growing species. For species that aren't native to limestone soils, you can use gypsum as a calcium source. Mike knows a lot more about this than I do, and he'll be more helpful on that front. Be aware of the fact that calcium needs to be balanced with magnesium, and a Ca-Mg ratio in the range of 3-1/4-1 is about right. I don't know what Mike does for Mg, but once again, he'll be more helpful on that front. Here's another good option -- a nitrogen-free Cal-Mag supplement like the one I mentioned in my last post. If you can't find a nitrogen-free Cal-Mag, there may be other options besides limestone and gypsum, although I don't know what they would be.

Tap water

• Pro (and this one is pretty big in my book) -- from LibreTexts Chemistry:
  "Hard water is water containing high amounts of mineral ions. The most common ions found in hard water are the metal cations calcium (Ca2+) and magnesium (Mg2+), though iron, aluminum, and manganese may also be found in certain areas. These metals are water soluble, meaning they will dissolve in water. " [My emphasis]
  With the hardness in tap water, your cacti will get plenty of Ca and Mg right from the source. (The tap water in L.A. isn't that hard, hence my reason for adding a nitrogen-free Cal-Mag supplement to the watering solution I use.)

• Con -- calcium bicarbonate, which combines hardness and alkalinity (Ca is the hardness, bicarbonate is the alkalinity). When you said that your tap water has a pH of about 8, you're measuring alkalinity, not hardness.

Alkalinity can be at least partially neutralized in acidic potting media. However, that's exactly what we don't want for most (if not all) North American desert species. With potting media that are pH-neutral or alkaline, acidification of tap water is required. By the way -- 50/50 rainwater/tap water only reduces the amount of calcium bicarbonate in your water, it doesn't solve the bicarbonate problem. If you don't want to bother with a pH meter, stick with rainwater, and be sure to provide suitable Ca and Mg sources for your cacti. But if you wouldn't mind bothering, I'll guide you on the ins and outs of using a pH meter to acidify your tap water.

What I don't know is how critical pH is to plant health - now I know that either too acidic or too alkaline will be very bad for the plant, but there's bound to be a safe range.

This should give you some insight:

pH_nutrient_ availability_ chart01.jpg (81.4 KiB) Viewed 3244 times

As we see, availability of all nutrients between pH 6.0 and 7.5 seems to be pretty much ideal. Even between 7.0 and 7.5 -- that kinda surprised me. This applies to all plants, not just cacti and succulents. Avoid anything that'll bring the potting medium down below 6.0 when you water, below 5.5 is just asking for trouble.

I'm aware my mix for the ferocactus is a little on the organic side. There is more perlite lower down, but I hate the stuff in the top layer because it floats (sadly I've been unable to get hold of pumice as an alternative). That said, I do intend to repot with less organics at some point in the near future.

I've insisted on gravel top dressing for many years -- partly decorative, partly to keep floaty stuff from getting all over my cacti. Tiny gravel (2-3 mm) isn't good because it holds too much moisture around the base. If you go with 4-5 mm or larger, that should be fine.

[MikeInOz]

Mike -- even though my cacti are getting Ca and Mg from acidified tap water, is adding 1/4 tsp. per gallon of the TPS CalMag okay, or could I bump it up to 1/2 tsp. per gallon for their last deep watering of the year this coming weekend?

1/2 teaspoon should be fine. But how do you register a Cal Mag product as ''organic'' ?

[Steve Johnson]

Mike -- even though my cacti are getting Ca and Mg from acidified tap water, is adding 1/4 tsp. per gallon of the TPS CalMag okay, or could I bump it up to 1/2 tsp. per gallon for their last deep watering of the year this coming weekend?

1/2 teaspoon should be fine. But how do you register a Cal Mag product as ''organic'' ?

Haven't a clue, you'll have to ask the manufacturer about that.

[Ilvin]

Unfortunately the original problem with my cactus has continued to spread. Mostly meaning there's spots on entirely different parts of the cactus now, while the original ones are only slightly bigger.

Its been outside, with full sun and lots of air movement, since I made this post.

Does anyone have any ideas of what this actually is? Or how I can stop it? its still only small patches now and I really do want to fix it before it becomes a bigger problem.

[Steve Johnson]

Unfortunately the original problem with my cactus has continued to spread. Mostly meaning there's spots on entirely different parts of the cactus now, while the original ones are only slightly bigger.

Its been outside, with full sun and lots of air movement, since I made this post.

Does anyone have any ideas of what this actually is? Or how I can stop it? its still only small patches now and I really do want to fix it before it becomes a bigger problem.

I'll answer your question with another question -- have you changed to a leaner mix with less organic material?

[ohugal]

Can you maybe post additional images of the current situation?
If it's a fungal infection, you can try a fungicide. Are there actually fungicides which work from the inside out? Does there exist something such as a systemic fungicide?
I agree with Steve a good cultivation practice is key to a healthly plant and a lot of usefull information was shared here. On the other hand, isn't there something which Ilvin can do in the short term to resolve his issue?

[MikeInOz]

I don't think it's a fungal issue from what I can see in the original picture. I don't remember ever seeing fungus infection start on the side of a cactus body. Most of the time it starts at the roots or - rarely - in the crown. If the problem is spreading and you cannot imagine an environmental issue like cold or humidity causing it, then it could be a problem such as pythium or verticillium starting in the roots and manifesting in the body of the plant here and there.
Fungicides don't really work on cacti, especially if it has penetrated the body of the cactus. The only remedy then is to cut off the infection if it's not too deep and dry the plant out for a long period and re-root it. It's won't hurt to bare root the plant and have a good look this time of year.

[Ilvin]

All right, it looks like the problem is.... root mealybug.

I've never had this issue before, but I've seen pictures online and it sure looks like it. I removed the cactus from the pot to find white stains on some of the roots, particularly the lower roots in the pot. Here are the pictures I took, my camera had trouble focusing on the problem.

skinspot1.jpg (83.87 KiB) Viewed 3069 times

roots1.jpg (163.4 KiB) Viewed 3069 times

roots2.jpg (134.99 KiB) Viewed 3069 times

roots3.jpg (162.16 KiB) Viewed 3069 times

So the first image if of one of the newer purple/orange spots. The rest is of the mealybug.

None of the roots were mushy, all the cactus body is firm, and I've now removed the rest of the soil from the roots.

The soil soak recommended in the pests post on this forum is not available in my country, so I'm now going to go soak the roots in 1% H2O2, which I figure should do the trick.

[Steve Johnson]

For good or ill, everything starts out in the roots -- and a root mealy infestation certainly does ill. Hydrogen peroxide is fairly effective, although I'll recommend soaking the roots in a 2% soap solution for about an hour. Plain old dish soap is fine, insecticidal soap even better. Be sure to thoroughly clean the inside of the pot too. When the roots are completely dry, repot in fresh dry mix and let them settle in for 2 weeks before watering. Now would be a good time to repot your Ferocactus in a mix with less organic material. Glad you caught the infestation before those root mealies had a chance to do more damage to the plant.

P.S. I realize that neonicotinoids are a no-no in most of the world, but Cyzmic CS is an effective alternative for soil soaks. Find out if you can get it in Australia.

[MikeInOz]

Malathion and imidacloprid are still available on ebay in AU.

[Steve Johnson]

Malathion and imidacloprid are still available on ebay in AU.

Well, color me surprised! Ilvin, go here...

viewtopic.php?t=42129

...and scroll down to the section called "Long-term solution for all types of scale insect". Percentage of Imidacloprid determines the dilution rate you should follow -- the example I showed you in my presentation is for 1.47% Imidacloprid. If the product you buy has a different percentage, you'll need to go with a different dilution rate accordingly. Good news is that your cactus growing season will be starting soon (if it hasn't already), so you'll be able to apply soil soaks to your Ferocactus and any other cacti you have. As the old saying goes, an ounce of prevention is worth a pound of cure.

[Ilvin]

I appreciate the information, but I won't use a general pesticide if soapy water will do the trick.

I've soaked the cactus roots in warm soapy water, I nearly went with a hot water bath but I chickened out. I want to save the cactus, not cook it. Then, I soaked the roots in 1% H2O2 for about half an hour. It dried out overnight and I've now repotted it in new, sterilized soil.

repotted1.jpg (90.01 KiB) Viewed 3009 times

Back where it started - hopefully minus the root mealybug.

Does anyone know if the purple and orange spots will resolve? I'm asking so I know what to look for to check the cactus is recovering.