My number ONE control for the common succulent/cacti pest is rubbing alcohol.
I keep a bottle available, next to my plants, at all times.
A bottle of 70% solution, with a squeeze sprayer from any cleaning solution bottle screwed to it, creates a simple, effective tool.

Squirt, Squirt the bug is dead. Direct contact will kill most all sucking insects.
The most common ones being mealy bugs and scales.
Unfortunately it has no effect on adult scales which have "armored" themselves, but it does kill the juvenile "crawlers".

My second favorite pest control is Ultrafine Oil Spray.
It works by smothering the insects. Simple and effective and safe to use.
Bugs cannot develop resistance to it like they can to chemical insecticides.
It does work on the "armored" scales.
Safer's Soap is just as good and works by the same principle of smothering.
NOTE: Only use the oil or soap sprays when temperatures are cooler.
Published warnings on the oil say NOT to use above 80 degrees F. or in the hot direct sunlight of mid-day.
Always better to spray for pests and diseases in the morning or later in the day to prevent from phyotoxicity. (burning or curling of the leaves)

I use ultra fine oil on all my plants: orchids, citrus trees, hibiscus, plumerias, etc.
I DO Not spray oil on succulents with the white, waxy, powder coating. It dissolves the "farina" waxy, white coating, which happens to be a natural protectant.

We can make this thread sticky if everyone makes an effort to keep the discussion on topic. I think there is a lot to be learned from the personal experience of the various members here who have kept succulents for a while. Thank you Bob for the initiative and for sharing what works for you.

I also use 70% alcohol in spray form as a quick and easy remedy for mealies and juvenile scale insects. I also use insecticidal soap (Safer brand), which as I understand it is just regular soap prepared with potassium instead of sodium in the base, in order to be friendlier to plants. I buy a concentrate and then make up what I need as I go. I think regular mild dish soap will also work fine at 1-2% in water if you use it in a focused manner and rinse thoroughly afterward the next time you water. It's the accumulation of sodium over time that will cause any problems, and that's something you can avoid. Soap itself (in reasonable doses) is pretty harmless to plants and their roots. One nice feature about the alcohol is that it will evaporate over time, and thus leave zero residue on the plant or in the soil.

I make a point to always spray when the sun is not out, so at dusk usually, or on a cloudy day. Part of that is to allow the product more time to work, and part of that is to prevent any kind of burn (which has never happened to any cactus or succulent that I have used alcohol or insecticidal soap on, and I never rinse until the next time I water).

I would also like to share some thoughts on mites and fungal diseases, but maybe it's better to focus on one thing at a time. The most frequent succulent pests here are mealies, hard scale insects, and aphids, and the two sprays I mentioned are my go-to first defenses when they appear.

I use rubbing alcohol in a spray bottle. It eliminates leaf miners that I had on aeoniums, aphids, and those small black mites. Keep plants in a shaded area after treatment.

Rot/fungus - use hydrogen peroxide in a spray bottle. It works on rust fungus, mold, algae, brown rot.

I too use 70% alcohol in a spray bottle or Safer's Insecticidal Soap. I tried mixing my own and although it didn't harm my plants (I used Castile liquid soap), it also didn't harm the bugs. The good thing about both alcohol and Insecticidal Soap is, because of the way it works, the bugs never build up a resistance to it. I usually rinse my plants after treatment but more because I want to wash the dead bugs away. Also, neither of these remedies will kill most beetles, caterpillars and slugs. Weirdly enough, Insecticidal Soap will kill ants though.

For hard scale, something with Dinotefuran as the active ingredient. I use it sparingly and as a last resort (sometimes I toss badly infested plants rather than play with the big guns). Its a systemic so I would never use it outside as its a broad spectrum pesticide and will kill anything feeding on any part of the plant (bees and butterflies included).

There is nothing you can spray on the outside of a leaf to kill leafminers. If you see they are gone after you spray, it was probably just time for them to morph into their adult form and fly away. Or, you damaged the leaves so badly, you killed the leafminers too.

Hydrogen Peroxide should never be used directly on a plant. Its a caustic bleaching agent and will react with anything containing moisture. If you see a fizzle when you spray, your plants will suffer for it at the cellular level. If there's no fizzle, the Hydrogen Peroxide has been reduced to water. It won't harm your plants but won't help either.

In all fairness the effects of peroxide are extremely dose-dependent. Concentrated peroxide is not good for your plants, dilute peroxide may provide mostly a placebo effect. I'm not a believer but I can't confirm or deny that it does anything. Don't use that stuff unless you know what dilution gives the desired result.

A mild dish washer soap is working great for me. But I also like to manually pick the yellow mites on adeniums with wet brush.

Somehow the dish washer soap here ever been advertised for washing fruits and vegetables, and the water from washing those also been used to water the plant as fertiliser. I assume it is safe for both plant and human, but can kill mites.

I'm hoping that this is the appropriate place to ask this question - I've had this cactus for a long time and it seems to be developing some kind of fungal/mould problem. It lives on my parents' front porch (which faces north) and so gets near full sun, good air flow and some exposure to rain. That said, we have had a wetter than usual year and so I suspect this is probably a factor.

One of the two stems also appears to be turning yellow and looks ill. Historically it has been damaged some years ago when it tipped over and broke the top section off both stems (in both cases they sprouted new growths and continued growing).



Cacti are not my area of expertise, so any advice would be appreciated. Some suggestions I have read are to cut out the infected tissue, or in the worst case cut off the healthy part and try to grow it from that (no idea if that would work this type of cactus, though, as I'm not even sure what type it is).

Do you know if there have been some sucking insects around? There is a type of stink bug that gets on my cacti and they cause damage that appears much like what I see in the photo. They fly and are good at hiding, so it pays to be watchful. They were a new pest for me about 3 years ago, but I learned to keep an eye out for them. They first year they hatched many nymphs and did a lot of damage to plants they selected. In subsequent years I've not had as much damage because I've been more watchful and they haven't reproduced in the same numbers. All I've used is insecticidal soap for control. I've used it as a contact spray. Where they puncture the skin, it may allow an entry point for other pathogens.

Thanks Donald. I'm not sure - I'll have to ask my parents to keep an eye out for any bugs on the cacti or nearby plants in my Mum's garden.

In the meantime, do you have any recommendations for treatment for the existing damage?

No, I don't. I thought the discoloration would eventually disappear as the plant grew, but it didn't. On the worst cases, where the spots developed black spots or the surface skin developed some necrosis they behaved like all those kinds of injuries and made permanent surface scars. Some of the necrotic tissue was the result of the insecticidal soap. Some plants seemed sensitive to it where others didn't react to it. The worst was a hybrid opuntia which I learned quickly I needed to rinse off the residue. The Echinocactus grusonii also was sensitive. That opuntia is a diva of a plant anyway, as it turns out . Some of the other small barrels didn't react at all as far I could tell. The problem with using it was that it needs to be used when you see the bugs. They are very mobile and very alert to danger to themselves. They will fly off if they feel threatened. The plant in your photo has a lot of smooth skin, so applying anything in the way of a contact spray residute might need to be rinsed off asap. The discoloration or scars won't grow larger, so as the plant grows they take up an ever smaller percentage of the surface. In that sense they recede, but the yellow never returned to being green.

Good luck. You may have something entirely different going on. You'll just have to watch the plant for a while. I'm not sure what else might cause the effect. Light, water, nutrients are all always something to consider. Sometimes plants just react to a change in location and throw a tantrum.

The scar looks ok, I am more worry on the yellowing stem of the cactus, it looks very ill, does it feel soft compare with the green one next to it ?

Kaktus said:The scar looks ok, I am more worry on the yellowing stem of the cactus, it looks very ill, does it feel soft compare with the green one next to it ?

Not sure. I will ask my parents to check and report back.

I've heard back from my Mum and yes, the yellowing stem is softer than the green one. She also took a few extra photos on her phone (apologies, the last one was late in the day and isn't well-lit):



Should I ask her to repot it and remove the yellowing stem?

I will watch the yellow one closely in a day or two to see whether it can heal by itself. If it become even softer than today, then possibly it has stem rot.
I will chop it until I have only the green color one. Make sure to apply fungicide on the wound. Usually the yellow is a goner.
Don't what's the suggestion from others

Thanks @Kaktus. I'll get my parents to keep a close watch on it over the next few days and if it declines, I will suggest to my mum to cut it back below the yellow part.

I was thinking today (more generally) about how we deal with new plants and the new pests they may be introducing to our local environment. So I thought I would share on this thread.

There is a certain dogma about quarantine, as if we would have a whole area with great light which could be reserved for new plants. Not to say that's not a great idea, if it's possible for you, but I have chosen an alternative which works given the lack of space here. I just put the new plants in the most visible place instead, of the various options available. Which for me is a shelf at about chest level right by the door on our rooftop balcony... right as I pass through I can let my eyes wander and see what's up with the newbies, with minimal effort or even intention.

So I guess I am replacing quarantine with a form of enhanced surveillance, or vigilance if you will. And it seems to work.

I will physically separate a plant with a florid bug problem, just on the obvious reasoning that the shorter the distance the bugs have to travel, the more likely they are to do it. But new plants go on that shelf next to everybody else (after a close inspection), and then I get to see how they respond to coming out of a box and being in new soil (as is most often the case), the sort of shriveling and unshriveling that are the aftermath of bare-root transport, the latter closely tied to the first deep watering, if the roots are in good shape.

The best treatment for most pests and diseases is prevention, a large part of which is just being aware of small changes before they spiral out of control.

And as I was hoping this thread could become a point of reference, let me show off a couple of my most wanted, with the idea of aiding identification.

This is the mealy bug.



It makes a cottony substance (presumably its nest and/or offspring) but the mature bug is big enough to feel when you pinch it between your fingers, confirming its demise.

Mealy bugs are incredibly slow moving insects. Simply removing them from the plant (by a jet of water from a hose) is often sufficient for treatment in the landscape. When you blast them from the growth center, or from the base of leaves near the growth center, you have made a big step toward keeping them gone.

They seem to arrive by air as well as by land. Their preferred method of delivery here seems to be the common ant. They most frequently appear here on Aeonium and some other Crassulaceae, but they seem to be incredibly equal opportunity herbivores, compared to some of the other common pests. Very much camouflaged (and sometimes impossible to detect without close inspection) on the white farinose type of plants.

There are mealy bugs that live primarily or exclusively in the soil, presumably feeding off the roots, and these are stealthier than the others (avoiding detection until a plant is unpotted, usually) but they are really susceptible to systemic insecticides (a drench in insecticidal soap may work great, too) and the treatment is usually for good, in my experience. I do not know enough about bugs to tell you if they are the same species as the others, but I suspect they are not.

Pictured below (with a bit of camouflage) are scale insects. The brown bumps in the picture, not the pink bumps which are part of the plant. So-called hard scale because it has a little shell secreted by the bug around itself as protection, once it locks down and stops moving. That shell is pretty good at keeping your first-line defenses (soap or alcohol spray) from working well.



Same family, slightly different treatment (mature scale bugs like barnacles need to be scraped off the plant for best results), soap and alcohol effective against the juveniles. If mealy bugs are slow, these are stationary (when full grown). Simple removal of mature scales is 90% of the solution for me, with a followup alcohol spray to zap the immature insects in the area.

Hello everybody, first time posters!
Our Aloe Arborescens has some black spots in her leaves.
We know also the mother of this little one had the spots.
Do you know what is causing it? Can be a fungi?

Thank you for your help!

@australis When I see a cactus yellowing like that and it is soft when squeezed I think it is dying. chop it off all the way down till you encounter green, healthy tissue. If no healthy tissue then chop it off at ground level.

The second cactus in the pot looks green & healthy. However, it is sprouting from where the original cactus was topped off. I would cut off the healthy top section right where it is sprouting from the bottom section. Right where it is the narrowest. Let the cut section heal or callus in a shady, dry location like your garage for a week or two. I have read somewhere to let it heal one week for each inch in diameter of the cut end.
Then cut a couple inches off the top of the old base section and leave it alone. Eventually it will sprout a new growth from the old base. I cut off the top to encourage growth from a 'new eye'. These plants always seem to grow out of the top where it is cut off. Therefore you need a new top (exposed eye) for it to sprout a new growth. You may want to hide this old plant out of sight since it doesn't look 'pretty' any more.

Once the healed top section is ready, it is time to plant it in a new pot with fresh mix. Use your normal, well drained cactus mix and fill up a gallon size pot about 1/2 way. stick your cactus into the mix an inch or so and support it with stakes. I use three tall stakes and tie them together at the top
Wait a week or so before watering and then water whenever it is dry. Do not over-water, but you do not want it to become bone dry since these are baby roots. When you see roots growing out of the bottom of the pot it is time to pot it up into its new pot. This is a slow process but worth the effort.
If you leave the cactus as it is now (growing from the cut off base) it will become top heavy and break off by itself. Not a pretty site since they can dent and break into pieces when they fall.

@OrchidBob - thanks for the detailed response. Years ago the pot fell over and the tops of both stems broke off. I don't think my mum was successful in getting them to grow, but we didn't know about leaving the cut piece to callus over for a week or two first at the time.

I am hoping to be able to transport this cactus to my new home over Christmas and then I'll be able to cut the healthy top section off and pot it up as you suggest. I'll have to check with my mum if she has cut the yellowing stem off yet (I asked her to do so if it continued to decline) and if not, to cut it back an inch or two above the previous break to expose a new eye.