Help! What Disease Have I Got?

[RichardMS]

Could someone please help me identify what is up with these seedlings of mine? The growing tips of these two year olds has/is turning a crusty brown, and white frosting is creeping down the plant - as is the brown crust. At first I thought it was damage caused by them being left under a leaky greenhouse vent this winter (that is when I first noticed the problem). I'm beginning to think it is red spider mite but as I've never had trouble with this before I would appreciate some advice.

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[iann]

The first picture made me think of scorching, but that wouldn't creep gradually down the plant. The last picture looks like it has rotted and is now being gradually consumed from within.

[RichardMS]

Thank you for replying Ian. I have persevered with these plants but this morning I threw four pots out. I don't know if the plants in them had rotted from the inside but they had shrivelled away to empty husks. Do you think rot is more likely than red spider mite? I kind of hope so as what I have read about these pests is quite scary! I am usually very mean with my watering but maybe when the winter leaks got to them the rot could have set in then. I don't have any experience of red spider mite - there are plants in the trays where these ones are that have not been affected, would red spider mite have spread rapidly to these other plants?

[BrianMc]

Third pic definitely looks like Red Spider Mite

[rodsmith]

Red spider mite can cause bad damage to a cactus epidermis but the damage is usually cosmetic and once the RSM has been dealt with, the damage usually grows out. If the cacti concerned were empty husks it suggests that they have rotted away inside, possibly from the leak during the winter. Some species appear to be more prone to RSM than others but it would be a bit surprising if it didn't affect some at least of your other cacti/succulents.

[Peter]

Has water been allowed to remain on these plants?

[eduart]

It looks like a Helminthosporium cactivorum attack to me, or a similar fungus anyway. Nothing you can do I guess, other than prevent. It typically comes from rainwater trapped for too long in the apical depression. My only doubt is that the plant lasted that long... Helminthosporium cactivorum usually kills a cactus much faster, sometimes within a week or so.

[RichardMS]

Thank you for all the advice and comments. The plants were damp in the winter and spring and water may have remained on them at times. I was expecting the damage to grow out but it doesn't seem to be doing so it seems to be getting worse but it doesn't seem to be spreading to adjacent plants, it is just getting worse on the individual plants affected. For now I will assume it probably isn't spider mite but a fungus/rot affecting the individuals? Would RSM have spread more rapidly?
These plants were from seeds i collected from my own plants and it was quite exciting to have germinated them - some are still thriving so I can't complain and will put it down to experience and think the survivors are stronger for the fact that they have been through the hell I exposed thgem to!

[anders]

For now I will assume it probably isn't spider mite but a fungus/rot affecting the individuals? Would RSM have spread more rapidly?

Could be both , an initial RSM attack followed by rot. Anyway, the grey patches and the darker, somewhat translucent brown areas say "rot" to me .

[RichardMS]

Thank you Anders. It makes sense. I guess a pest weakening a plant could lead to complications such as rot. Maybe I should have concentrated on the symptons on the first two photos. It is like a brown crust. Could this be RSM and if so how quickly would it spread to adjacent plants? If it will grow out when would I expect to see new growth - the plants don't seem to be growing at the moment.
Eduart: Would the brown crust be a sympton of Helminthosporium cactivorum. Are the plants gonners? there are some in the same tray that seem to be growing happily so is this ailment non-infectious?