I'd like to get some advice on an occasional problem with my semps. Every now and then, the largest rosette on a semp will start rotting. If I remove it, there is no further rotting. This has happened on Jublilee, Red Heart, Kramer's Spinrad, Quintessence, Wunderhold, Lennix's Glory. and a NOID. Normally, I would suspect overwatering but I don't think that's the case. With our cool winter temperatures, I've only watered about once a month. The soil is well draining. Is there another problem (bacterial?), or is this just something that happens with semps occasionally? Is there anything I can do or check?

Thanks in advance for any advice you have,
John

Hi John. There are a number of things that could be happening:
1. The older rosette could have a buildup of dead leaves, causing excessive moisture to the underside of the rosette leading to rot.
2. Check the crown/roots to see if there are signs of pests. Roly-polies don't count, they eat dead plant material. Grubs are common culprits.
3. There are many semps that are genetically prone to rot.
Hope this was helpful?
Photos of the rotting semps might be helpful, top and underside.

In my part of CA there's a serious problem with crane fly larvae. They eat the roots of Semps, and echeverias. They occasionally eat them inside out. Here in the mediterranean climate, there are hot dry summers, with cool wet (ish) winters. The winters and spring cause plenty of rot problems, and they are the time when the larvae are active.

Lynn, Evan,

Thanks for your suggestions.

I don't think it's rot caused by build-up of dead leaves. None of them had excessive dead leaves.

It may be these semps are genetically prone to rot. I'm surprised that it only seems to affect the largest, central rosette.

The issue of grubs is an interesting one. I don't have any pictures of tops and bottoms. The next time I find rot, I'll take some. I did look at them closely. Only one of the semps ever had evidence of grubs. It had small white larvae that were about 1/8 inch long. The other semps had no signs of infestation.

We did have many adult crane flies last fall. Do they have white larvae? I thought they were larger and brown. And are they that small?

I'll have to pay more attention if/when it happens again.

John

Rot can also be caused by fungal things or bacteria

Also check to make sure the soil is not compacting and is draining well. Lots of top dressing with small/sharp gravel or chicken grit.

I've had main rosettes with their main root hollowed out by what I thought were grubs.


Here's some more critters right at the site damage

Those are milliepeds/scenty pedes

It looks like the soil might to compacted, so it becomes too water-holding, which invited milipedes and isopods. millipedes do not hurt the plant, only eat dead material (at least for me)

I have those exact species, they don't rot/harm my semps

Great photos Bev. Most of what I see are the cleanup crews (Roly-poly, millipeds). I do see one grub in the last photo.
Root aphids, fungus gnats and mealy bug are other root damaging pests.

Since I was in my semp bed photo file, I have to show off pic of my 2014 grub collection (again)....

Looks like a japanese root eating beetle.

Thanks all for suggestions. (Great photos, Bev.) What I saw on one semp didn't look like any of the photos supplied by Bev and they didn't look like the online photos of root aphids, fungus gnats and mealy bugs. I only saw the small larvae on one of the affected semps so I'm not sure what that means. I think I'll have to see what happens (and it only happens occasionally) and take pictures to post. But it doesn't sound like this is just rot that occurs every now and then. Pretty sure it isn't just rot because we had no rain for two months and I only watered once each month when the soil was really dry. I'll keep an eye out and report back. Again, thanks for all the comments.

John

John, I split this off the Chat forum, and created a new thread titled 'Sempervivum pests'.
This way it will be easy to find and add to the discussion.

Thanks for doing that.

John

Instead of waiting for a semp to rot out, I pulled a semp rosette that looked like it was in the beginning stages of rot. The roots looked healthy but the leaves were starting to go. Here is what I found:

This is not a great photo. My camera can't focus any closer but I think you can see three white spots on the soil taken from the plant. I think those are root aphids. They are less than 1/16 inch in length.

In contrast to what I found on the internet about root aphids, these are not especially triangular in shape (instead longer) and they move fairly quickly (but I understand there are many types of root aphids). They are white and the right size.

Also, in looking at the semps affected, I realize that they are all in the middle third of the bed so proximity is also a factor on which plants are affected.

Now, I have to figure my next step.

John

Do they jump? If they do jump, they may be the harmless springtails.

No, they don't jump. They're almost grub-like.

John

It does look like root aphids.

Lynn,'

Thanks for the confirmation.

John