Could be powdery mildew.
If it is, topically applied sulfur powder is supposed to help with this, but the spores can hang out in the potting medium. The medium needs to be changed out or treated also.
You can try mixing in one level teaspoon into 16oz of water and spray all parts of the leaves very thoroughly, stems. Agitate the mix frequently to keep the powder suspended. Let the powder dry on the leaves.
https://www.amazon.com/dp/B000HA95W2
This is the treatment that I'm currently using on some African Violets.
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I've gotten to the point in my plant-cultivation "maturity", that I can much more easily let a plant go into the trash for certain issues. Plants are too ephemeral to attach an emotional value to them...or spend tons on money on just one plant. 😁
I have a hard limit on max $25US for orchids and $10 for everything else.
I do however like to experiment as a learning process to see what works or doesn't in my grow-space for various plant issues.
If you've never tried to treat powdery mildew, this might be a good learning experience. Or not. 😊
Could be powdery mildew.
If it is, sulfur powder is supposed to help with this, but the spores can hang out in the potting medium. The medium needs to be changed out or treated also.
You can try mixing in one level teaspoon into 16oz of water and spray all parts of the leaves very thoroughly, stems. Agitate the mix frequently to keep the powder suspended. Let the powder dry on the leaves.
If it's powdery mildew...which tends to be more grayish in color from what I've seen, you can treat with sulfur powder. You can try regardless...it won't hurt anything.
Micronized sulfer powder: https://smile.amazon.com/dp/B000HA95W2/
I mixed in one teaspoon to 16 oz water. Apply with a spray bottle. Let dry so the powder remains.
Also treat the soil with the same sulfur-water or water in some powder as mildew spores can reside in soil.
Pretty specimen!
I've started adding in a little micronized sulfer powder with my potting mix after I found out that it seemed to conquer my spider mite problem.
And then those plants that previously had spider mites, and thrips issues (currently conquered), I mix some of the same powder with water and apply it to the substrate surface via a squeeze bottle. I probably do this once a month. This is not a standard watering amount....it's more like a topical application.
What I purchased:
In my experience, the color black in the botanic world is never a good thing. Shades of brown...okay to tolerable, black -- no.
There is also a spot slightly further back on the stem adjacent to the sheath connection point that is also not looking good.
Depending on what implement you used to prune the plant, you might have introduced an infection if you did not sterilize it beforehand.
An alternative thought, before the plant calloused over, an infection of some sort set in and has possibly spread further into the stem.
Typically, if a plant was pruned while healthy and the cut point will take awhile to callous over (large area/thick stem, high moisture), sulfer powder or cinnamon powder is applied to act as a preventative antibacterial. For some of my plants...I've used hot glue to seal the cut point especially if it will be exposed to a lot of moisture...but the area has to be 100% healthy.
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What I would do...cut the stem back below the secondary point I mentioned. Use a blade that has been sterilized with isopropyl alcohol or flamed.
Cover the cut with sulfer powder or baking cinnamon powder. Since this plant looks to be outside, you might need to reapply daily for three days depending on your weather conditions.
Keep an eye on the plant in case you need to cut back further.
Rot is the cancer of the plant world. One remaining speck on a primary structure like the main stem can spread rapidly. The rot has to be excised with clean margins...just like cancer surgery and then followed up with antibacterial treatment and monitoring.
Micronized sulfur powder....
I bought micronized sulfur powder, mixed it with distilled water in a spray bottle. Sprayed it on, rubbed each and every leaf, petiole and primary stem....abaxial, adaxial, every nook and cranny and used a baby-soft toothbrush to assist. I wore rubber gloves just because.
After the rub down, gave the whole plant another spray, watered with this same sulfur-water and then let the powder dry on the plant.
I left the sulfur-powdered plant sit for three weeks out of direct sun in a location away from my other plants. This three weeks was to whack any stragglers due to life-cycle stages/late emergence. At the end of three weeks, I hand-wiped off the powder on the adaxial side of the leaves so they would look pretty and then acclimated the plant back to its window location.
After battling spider mites since October 2021 with very diligent DIY treatments (and repots...so change of soil), this seems to be doing the trick. It's been over three months since I started using the sulfur regimen. I also did this treatment to my dieffenbachia...same positive result.
The label says it's good for mites, thrips, and scale...the evil trinity of plants all over the world.
https://www.amazon.com/dp/B000HA95W2
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As mentioned in an earlier comment, I also suggest cutting off the stems with the worst infestation/damage as the leaves are going to continue to die....or just remove the leaves. Be aware that the plant will seep a white sap that can be skin irritating.
Because of the sap, I would treat first, then prune to whatever degree you feel comfortable. Immediately afterwards, sterilize the pruning tool with isopropyl alcohol or flame, wipe down your work surface with isopropyl alcohol, wash your hands and change your top before you deal with any other plants.
I also inspected and prophylacticly treated the immediately adjacent plants. I timed this treatment after they were out of the direct sun so I could put them Immediately back in their spot.
To address the leaf browning issue....it could be rot that has infected the plant. It could be mechanical trauma to the leaf. It's difficult to say.
There is a chance that it could stop at this point or continue to advance. Sometimes plants take care of themselves and will isolate an infection.
A stop-gap measure....sprinkle on a little bit of baking cinnamon powder on the spot. It acts like an antibacterial.
Or....if you happen to have some sulfur powder on hand (but I'm guessing you don't) you can brush a little bit on the site. https://www.amazon.com/dp/B000HA95W2
Try not to let this area get wet.
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To be a debbie-downer, I had a pot of three pleiospilos compactus and two rotted before I realized what was going on and with one of them, there was no overt signs of issues.
My remaining plant (now over two years in my care)....I just discovered about ten minutes ago....is popping out a new leaf pair. 🎉
My spider mite treatment....
I use a treatment of micronized sulfur powder mixed in water. One teaspoon to 12 oz distilled water. Spray bottle application. Shake frequently to keep mixed. Basically drench the plant, top/bottom of leaves and any other nook and cranny.
I let the water evaporate leaving a coat of sulfur powder on the leaves. Visually inspect every five days. Keep out of direct sunrays during treatment period. After six weeks (just for good measure), I rinse/wipe down the leaves' adaxial side so they look pretty-er.
During this whole process, I also work some of the powder into the soil and water-in. Subsequent waterings, a portion is sulfer powder infused water first followed by whatever volume of water is needed or visa versa depending on the plant.
Fingers crossed.... I think this technique is working after having tried various other DIY and commercially purchased items. Started using it mid-July this year. No further spider mites detected on my four chronically infested plants....ficus elastica, dieffenbachia, anthurium, and syngonium.
https://www.amazon.com/dp/B000HA95W2
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Redditor....Kattorean suggested this treatment which I have as a backup plan if everything else fails....
"For all infestations, I coat the plant in pyrethrin & seal it up in a bag overnight, rinse the carcasses of [sic] in the morning.
It's a neuro-toxin to insects on contact & will suffocate the scramblers with the camphor in it.
Won't harm your plant. Usually only need one night in the bag."
Other comments by her suggests that another 24-hours might be needed in the case of really extreme infestation.
I would also start using the sulfur powder worked into the soil so the plant/s develop systemic protection.
I'm using this micronized sulfur powder for spider mites but the label also says for thrips and scale. You should be able to get this in Canada.
https://smile.amazon.com/dp/B000HA95W2/
In a spray bottle, I mixed one teaspoon in 16 oz of distilled water and added a couple of drops of castile liquid soap. Sprayed the plant and the soil. You'll need to reshake the bottle frequently to keep the powder suspended. Let it dry.
Keep the plant out of the direct sun during treatment. Carefully recheck once every five days for three weeks after the first treatment. I left the power on for three weeks and then sprayed the leaves off.
So far, no recurrent spider mites on my dieffenbachia or ficus elastica.
I'm using this for spider mites but the label also says for scale.
https://smile.amazon.com/dp/B000HA95W2/
In a spray bottle, I mixed one teaspoon in 16 oz of distilled water and added a couple of drops of castile liquid soap. Sprayed the plant and the soil. You'll need to reshake the bottle frequently to keep the powder suspended. Let it dry.
Keep the plant out of the direct sun during treatment. Carefully recheck once every five days for three weeks after the first treatment. I left the power on for three weeks and then sprayed the leaves off.
So far, no recurrent spider mites on my dieffenbachia or ficus elastica.
You need to recheck your plant without fail once every seven days for at least twenty-one days to whack any life cycle holdovers.
If you caught this early enough, no soil treatment but if you want to be proactive, you can buy micronized sulphur power and work a little of that into the soil. Wear a face mask when working with it and turn off any fans. Once it's wet/in the soil...then mask off, fan on.
You can order sulfer powder like this...https://smile.amazon.com/dp/B000HA95W2/ . It's a sure-fire form of treatment if it's fungal in nature in conjunction with going scorched-earth removal of the "black".
I consider anything like this to be treated like a cancer. Removal needs to be down into healthy tissue so there are clean margins. If even a spec remains, it can still rapidly spread.
I would normally sprinkle a little cinnamon powder to help facilitate callousing.
If you can place the plant under filtered light...especially if you're experiencing a heatwave, it will help reduce stress on the plant while it's recovering. Then you can slowly adapt it back to its usual spot.
Looks so different on grape! It’s obvious on my cucumbers and squashed. An actual powder. This looks like rust or fungus. Interesting.
This what i want ?
Bonide BND141 Sulfur Plant Fungicide Organically Controls Rust, Leaf Spot and Powdery Mildew, 1 lbs, Ready-to-Use https://www.amazon.com/dp/B000HA95W2/ref=cm_sw_r_cp_api_i_ZPCHEGKAE3DJET7TKFH6
Walmart should have it, or most garden stores.
And of course Amazon
Bonide BND141 Sulfur Plant Fungicide Organically Controls Rust, Leaf Spot and Powdery Mildew, 1 lbs, Ready-to-Use https://www.amazon.com/dp/B000HA95W2/ref=cm_sw_r_apan_i_FR18E0MTB0V3C1ABT7GH
This looks like cobwebs to me. A good thorough rinse off is probably all you need.
Examples of pests via PausedFox.... Tap on Example 3 under Spider mites.
https://www.reddit.com/user/PausedFox/comments/j4n6e3/common_houseplant_insects_and_example_photos/
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If you want to be proactive for just-incase, this is what I use to treat spider mites.
I've very recently added to the pest treatment regimen using micronized sulfur powder mixed with water. Because the powder is very fine, I suggest working with no air blowing and/or a mask when working with the dry powder. Once the powder is wet, then no mask. It's been suggested to also wear gloves as the sulfur smell can cling to your hands. I'm mixing one level teaspoon into 16oz of water.
This is what I purchased: https://smile.amazon.com/dp/B000HA95W2/
I'm using this in lieu of a DIY mix on a few mite-magnet plants...ficus elastica, dieffenbachia, a peperomia, and a syngonium. I also mix a half-teaspoon of the powder into the top layer of the potting soil for any fallout mites.
Application is via a spray bottle but it took me two tries to find a squeeze-sprayer that doesn't get clogged up by the powder...even though it's micronized. You do need to agitate the solution frequently to keep the powder suspended. A surfactant could probably be added but I don't want the soap residue (see below why).
Started using this July 2022 and have had no reinfestations.
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From a previous comment I posted....
To read: https://exoticpetsworld.com/red-spider-mite-life-cycle-how-to-identify-prevent-and-treat/
Key items for spider mites....
Physically rub ALL the surfaces to remove webs and adult mites...every nook and cranny. Topside, underneath, leaf tip to soil level. Get a very soft brush like a baby toothbrush or post-op oral surgery soft brush and use it. Spider mites (and thrips) particularly like young vegetation and can hide in the sheaths.
Repeat¹ treatment every five to seven days for three to four cycles...regardless if you see signs of infestation to catch all phases of the life cycle. This is why people fail to fully eradicate the pests...the life cycle is not broken....they do one treatment and stop or there is too much gap-time between treatments.
Treat the soil surface also.
Preemptively treat adjacent plants for at least two cycles.
Do not expose plants to direct sunrays during treatment. They are in a somewhat weakened state and need time to recover.
Be sure to wash your hands and possibly change your clothes before you start working with other plants so you don't transfer.
As far as DIY treatments and purchases...
I'm not convinced from various readings that neem oil specifically is the end-all, be-all treatment form. But horticultural oils are beneficial and can be formulated from petroleum or plant-based products.
Anytime dish soap is recommended as a surfactant in a DIY "recipe", it might not be the best thing for the plant due to chemical additives. Castile-type, vegetable-based soaps are recommended instead.
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¹ Instead of having to respray when I used the DIY recipe, I let the sulfur powder dry and remain on the leaves for twenty-one days (life cycle span). After that, I wiped off the residual powder on the adaxial side of the leaves on the ficus elastica. For the other three plants, I've let the powder remain as it doesn't show up like it did on the ficus.
Try either a very sharp knife and wipe the blade with 70% isopropyl alcohol or flame the blade first.
Or, I've seen unwaxed dental floss used a la garrote-style to behead.
Because the plant is so juicy, it will take a while for it to callous...like days and days.
You can apply sulfur powder to decrease the chance of rot setting in. https://www.ndsu.edu/pubweb/chiwonlee/plsc368/student/Papers05/jennifer%20brause/Cacti%20Propagaton.htm
I use this: Micronized sulfer powder: https://smile.amazon.com/dp/B000HA95W2/
This is a pretty good propagation guide. Skip down to columnar cactus.
https://succulentplantcare.com/how-to-easily-root-and-propagate-a-cactus/
Definitely stake the plant like you currently show. Additionally, you can add an inch or so of pumice to help stabilize the plant without it impacting moisture evaporation. After you get the roots established and incrementally adapted back to the grow-light, try and make sure it gets prime space -- directly underneath the light.
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What I would do when potting after callousing, set the plant at the proper level in the mix, with the potting mix level about a half-inch below the pot rim. Cut up plastic cups (like Solo plastic cups), into pieces (top to bottom) and fit the pieces around the perimeter of the pot to create a collar¹ about 1.5 to 2-inches tall. Then add the pumice to help stabilize the plant. Once the plant is established, you can remove the collar and the extra pumice. The plant and substrate will be the correct level in the pot.
It's important that you don't jostle the plant while it's rooting.
Make sure the pot is not too large. If your cactus is two inches in diameter, use a 3 to 3.5-inch pot.
Make sure the new medium has a higher percentage of inorganic to organic components.
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I can DM you an example if you are interested. Just let me know.
••• Spider Mites...
You needed to retreat every five to seven days for a period of no less than 21 days to whack the various stages of the spider mite life cycle.
For this level of infestation, repotting is typically in order as the soil could be infested also.
Once spider mite damage occurs, the affected leaves will often times continue to decline depending on how severe the infestation was even if treated.
Severally damaged plants are often prone to other infestations due to the weakened state. So be sure to do regular inspections.
••••••
I've very recently added to the pest treatment regimen using micronized sulfur powder mixed with water. Because the powder is very fine, I suggest working with no air blowing and/or a mask when working with the dry powder. Once the powder is wet, then no mask. I'm mixing one level teaspoon into 16oz of water.
This is what I purchased: https://smile.amazon.com/dp/B000HA95W2/
I'm using this in lieu of a DIY mix on a few mite-magnet plants...ficus elastica, dieffenbachia, a peperomia, and a syngonium. I use this on the plant and also do a watering with it to treat the soil.
I use it in a spray bottle but it took me two tries to find a squeeze-sprayer that doesn't get clogged up by the powder...even though it's micronized. You do need to agitate the solution frequently to keep the powder suspended. A surfactant could probably be added but I don't want the soap residue (see below why).
I'm also mixing half-teaspoon of the powder into the potting mix for my new plants as a preventative.
Started using this July 2022 and have had no reinfestations.
•••••
From a previous comment I posted....
To read: https://exoticpetsworld.com/red-spider-mite-life-cycle-how-to-identify-prevent-and-treat/
Key items for spider mites....
Physically rub ALL the surfaces to remove webs and adult mites...every nook and cranny. Topside, underneath, leaf tip to soil level. Get a very soft brush like a baby toothbrush or post-op oral surgery soft brush and use it. Spider mites (and thrips) particularly like young vegetation and can hide in the sheaths.
Repeat¹ treatment every five to seven days for three to four cycles...regardless if you see signs of infestation to catch all phases of the life cycle. This is why people fail to fully eradicate the pests...the life cycle is not broken....they do one treatment and stop or there is too much gap-time between treatments.
Treat the soil surface also.
Preemptively treat adjacent plants for at least two cycles.
Do not expose plants to direct sunrays during treatment. They are in a somewhat weakened state and need time to recover.
As far as DIY treatments and purchases...
I'm not convinced that neem oil specifically is the end-all, be-all treatment form. But horticultural oils are beneficial and can be formulated from petroleum or plant-based products.
Anytime dish soap is recommended as a surfactant in a DIY "recipe", it might not be the best thing for the plant due to chemical additives. Castile-type, vegetable-based soaps are recommended instead.
•••••
¹ Instead of having to respray when I used the DIY recipe, I let the sulfur powder dry and remain on the leaves for twenty-one days. After that, I wiped off the residual powder on the adaxial side of the leaves on the ficus elastica. For the other three plants, I've let the powder remain as it doesn't show up like it did on the ficus.
Could be powdery mildew. It's insidious stuff.
Spores can remain in the soil necessitating a repot using fresh soil.
There are several ways to try and treat the affected structures...
Wipe the leaves and affected areas with whole milk (not low-fat, soy, oat, etc...the real dairy stuff).
Wipe the leaves with the liquid whey derived from yogurt. I think this is diluted with water but I'm not sure to what degree. You can watch this video for more details: https://youtu.be/2nOCODmQsIo
Purchase micronized sulfur powder, mix with water¹. Spray/wipe down the structures and let dry. After the wiped down, respray and let the residual powder stay on the plant for a couple of weeks until your indoor environment changes (heat/humidity).
Micronized sulfer powder:
https://smile.amazon.com/dp/B000HA95W2/
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¹ I mix one teaspoon with 16 oz of water and dispense via a spray bottle. But you have to constantly agitate the bottle to keep the powder suspended.
This has also been very effective in treating spider mites.
First, start by donning rubber gloves, eye protection if you don't wear glasses, and long sleeves as this plant has toxic sap.
I would then make my first cut at the narrow, leafless point near the base of the stem with sterilized knife/shears/scissors...isopropyl alcohol or flame the blades.
Then for the new segment, cut off several inches off of the bottom bare stem The whole top portion you can water-prop as is or cut it into two pieces.
If you cut into two pieces, strip off the lower leaves of each section along with the sheath and put both sections in water with the waterline being below the lowest leaves. Any current leaves that are below the waterline will eventually rot and pollute the water. The cuts that are above water or soil, I sprinkle on a little baking cinnamon powder to promote callousing and to act as an antibacterial.
I use distilled/RO water for my props of this nature. You will need to change the water routinely and occasionally rinse off the lower stems if they get a little slimy.
Place in a bright location, no direct sunrays other than maybe an hour or two morning sun.
Place the pot with base stem in an east-facing window. Water as per environment requirements and new growth should pop out on it. Since you said the plant appears to be healthy, treating rot should not be an issue. But be aware, with no foliage to consume moisture, watering frequency will be changed to greater intervals. There is a chance that the plant needs a repot/soil refresh regardless if you prop or not.
When the plant has very robust roots...primary, lateral/secondary, and you start seeing new leaf growth...time to traditionally pot....which is a different discussion and one that is about two to three months on down the road based on my propagation timing philosophy.
If you decide to cut the top portion into sections, I'm happy to mark up a picture via DM for you. Let me know.
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I'm in Houston, Texas. This plant is a spider mite problem for me. But I think I now have the issue conquered. Initially, I sprayed the whole plant with sulfer powder mixed with water and let dry. I intermittently watered in sulfer powder. And now, I add it to my potting mix so the sulfer becomes systemic and so far, so good.
The perils of outdoor or indoor gardening.
Don't worry. Huge chance they will survive to split, flower, etc. If they decide to die sometime in the future, it probably won't be from this injury.
The wounds look like they have already started callousing over. You could give a light sprinkle of baking cinnamon powder to help promote callousing and act as an antibacterial.
If you have some sulfer powder on hand, you can brush a little on.
https://www.amazon.com/dp/B000HA95W2
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Cat injury:
Squirrel injury:
https://www.reddit.com/r/Lithops/comments/psjde0/the_squirrels_chose_war/
https://www.reddit.com/r/Lithops/comments/qjxrff/twas_eaten_by_squirrels_about_2_months_ago_but/
Dog nibble:
https://www.reddit.com/r/Lithops/comments/vm4sv9/dog_got_it_is_there_anything_i_cano_do/
Toddler attack:
https://www.reddit.com/r/Lithops/comments/umn8o2/caught_toddler_halfway_lost_cause/
Great cultivation info!
It sounds like the plant has some type of fungal/bacterial issue. And because the onset after purchase happened so quickly, there is a chance the plant came home with these issues. Being in a new environment caused the condition to speed up and manifest itself in the black spots and leaf loss. The fact that the new leaves have it is a major indicator in my thinking.
BONIDE PRODUCT 141 SULFUR PLANT FUNGICIDE, 1 POUND https://www.amazon.com/dp/B000HA95W2/ref=cm_sw_r_cp_api_i_O8D4Ab5AMCXQ0