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Since May 2018 I’m testing the “hot bath” procedure against mealybugs. It is something I read elsewhere and decided to try. No plants showed signs of stress after the procedure, so I think now I can share it.

The idea is to immerse the plant in hot water for some time, to kill the mealybugs and its eggs.

First I did an experiment to see if the plants would be damaged by hot water. The following plants were submitted to the experiment: Hylocereus sp., Opuntia robusta monstrose, Huernia kenyensis, Sedum sp. and Haworthia mutica.

The temperatures and time length tested were:
60 C for 1 min
55 C for 2 min
55 C for 5 min
50 C for 10 min
45 C for 15 min
After the time lapsed, plants were immediately immersed in cool (room temperature) water for 5 minutes.

Results: At 60 C the Hylocereus looked cooked. But about 15 days later it was showing new branches and it is alive until now. The other plants suffered no visible harm in any of the treatments.

This gave me courage to do it systematically with any new acquired plant, to minimize the entering of mealybugs in my collection, since plants from supermarkets, for example, are all carrying lots of mealybugs.

So I wash the roots in running water, then submit the plant to a given temperature for a given time, and then put the plant in cool water. I let it dry and plant it in a few days, with my mix (the original substrate of the plant is discarded far from my plants).

In the table below you can see the plants that passed by the procedure until today. All of them had the size of a ping-pong ball, or smaller. None seemed to suffer, except for the Parodia halsenbergii, which, however, recovered already.

When repoting plants is a good opportunity to do this procedure as well.

Another thing I do systematically is: whenever I repot a plant, I throw the substrate in a baking tray, and when it is full, I bake it in the oven (for 200 C , 30 minutes, or so…). All repoted plants receive a new substrate.

Here is the Table mentioned above:

Deleted

Never would have thought of that, I'd be too scared to try but since you went ahead and did it I'll have to remember this page in case I ever encounter the root mealies. So far I've been lucky enough to not have any but I suppose it'll happen some day, especially since I just bring home plants and repot them with the store soil still mostly intact (they're probably around in there somewhere). Still the occasional surface mealy bugs, but nothing too disastrous yet

Very good experiment! I can also say i used it for haworthia limifolia with 0 damage whatsoever. I wonder if schlumbergeras can take such high temps?

Thank you for this valuable info!

Interesting. Never tried the hot bath method. Thanks for the useful info/tips.

I've just discovered root mealies on one of my Mammillarias I'm wondering: It needs repotting anyway -- would spraying and cleaning the roots with a spray hose be sufficient to wash the mealies away? Or do the nests 'stick' to roots? Should I try the hot bath method as well (or should I wait it out, as it might mean too much stress all at once on the roots)?
Does anyone have an opinion on what the best route would be?

saboten wrote: ↑Thu Nov 29, 2018 9:17 pm I've just discovered root mealies on one of my Mammillarias I'm wondering: It needs repotting anyway -- would spraying and cleaning the roots with a spray hose be sufficient to wash the mealies away? Or do the nests 'stick' to roots? Should I try the hot bath method as well (or should I wait it out, as it might mean too much stress all at once on the roots)?
Does anyone have an opinion on what the best route would be?

If one plants has them, probably all of them have them. Soak the roots in hot water or soapy water. Their skin is hydrophobic so water doesn't actually "stick" to them and thats why uou need soap. Cacti are generally very forgiving of all these stressful root procedures.
I've fiddled with all of these methods but found the best is to use a systemic insecticide once and for all. I tried acetamiprid and even my severly infested cacti reacted in a couple of days and started a growth spurt

I'm finishing another experiment to post a complete report here but I discovered that 47 C Celsius is not sufficient to kill mealybugs. I tried 55 C and they finally died. The plants tested are alive, but I am not this confident to submit precious plants to this temperature.

mmcavall wrote: ↑Sat Dec 01, 2018 5:17 pm I'm finishing another experiment to post a complete report here but I discovered that 47 C Celsius is not sufficient to kill mealybugs. I tried 55 C and they finally died. The plants tested are alive, but I am not this confident to submit precious plants to this temperature.

I'm not surprised they weren't killed at 47 deg c. I guess that soil surface tempertures would routinely get that warm in full sun situations.

So what about hot soapy water as step 1 of a new experiment and hot soapy water with contact insecticide as step 2?

Hi Elie,
I would never use soapy water as it is poisonous for the cactus. I do use methylated spirit:
Get methylated spirit and either spray it onto the plant or apply it with a qtip. When the white wool turns dark and reveals even darker spots inside (the bug inside its wool), then you have mealybugs.
The methylated spirit does not harm your cactus but kills mealybugs and other insects. I use it since I don't know when. When I fear the bugs sit in the earth, I uproot the plant and bath the roots, too.
Never had any problems.
N.

ElieEstephane wrote: ↑Thu Nov 29, 2018 9:52 pm If one plants has them, probably all of them have them.

Hello Elie

How have you been? Very good I hope.

This is just an FYI kinda thing ... a story of my experience. I don't say that anyone else that ever experiences anything like this will have a similar experience ... this is just a "this is what happened to me" story and anyone that reads it should take it for what its worth.

I don't have a lot of room to grow things. But I DO have a fair number of containers. Which means things are a little crowded. I had never had any problems with any kind of pest ... right up until the time that this occurred. One day I noticed a cactus with VERY dense spines, that was about 8 inches tall was beginning to lean to one side at just about the point of 1/3rd of its height up from the top of the soil.

On close inspection, I noticed a mealybug infestation. An infestation that was SO bad that all I could see in the spines was this mass of bugs squirming and swarming over each other. I couldn't even see the skin of the cactus at that height. It didn't cover the whole cactus, nor did it wrap completely around the cactus at that height. But on that ONE side, at about one-third of its height above the soil, the bugs were so thick that it was like a horror movie. I very nearly dropped it on the floor in sheer disgust.

I immediately took it outside, as far from where I live as the water hose would reach, and removed the mealybugs with a pressure stream. That worked. It took a few minutes, but it worked. I immediately ordered a systemic insecticide to prevent any other contamination. An examination of the roots did not reveal any underground contamination. I also left it outside fearing that It might expose the rest of the plants that had been surrounding it on the inside. And it didn't come back inside until it had gotten a pair of systemic insecticide treatments.

But nothing else around it ever got even the first mealybug. I was completely astounded, although completely grateful, that nothing else got the bugs. I have NO explanation for this. Nor have I intended this to be a cautionary tale of any sort. It is just a thing that happened to me and I leave it to those that read it to shudder, hoping that this NEVER happens to them.

Be safe my friends. Be VERY careful in your traveling. It only takes ONE fool-in-a-hurry-to-get-somewhere-not-watching-what-they-are-doing to ruin the rest of your life!

nachtkrabb wrote: ↑Fri May 24, 2019 8:44 pm Hi Elie,
I would never use soapy water as it is poisonous for the cactus. I do use methylated spirit:
Get methylated spirit and either spray it onto the plant or apply it with a qtip. When the white wool turns dark and reveals even darker spots inside (the bug inside its wool), then you have mealybugs.
The methylated spirit does not harm your cactus but kills mealybugs and other insects. I use it since I don't know when. When I fear the bugs sit in the earth, I uproot the plant and bath the roots, too.
Never had any problems.
N.

Pure soap is not poisonous to the cacti, but some soaps may have additives that are. Anything sold as insecticidal soap would be safe.