Help! What Disease Have I Got?

[3bears]

spider mites are very easily observable with a magnifier. you can see them with the naked eye also, and they move. if you don't see them, it's not spider mites. like spiders, they spin web if undisturbed. i do not find them to be a problem and blast them away with hose spray.

[Chris43]

Mention was made of the plants being just husks, and empty inside. Could this be a case of sciarid fly grubs? It is so long since I used any appreciable amount of peat in my compost that I really can't remember exactly what the results were like, but I seen to remember the plant looking sick, and then effectively collapsing as the skin had become brittle, and nothing inside. These were seedlings, probably (at the time) Rebutias or Echinopsis.

[eduart]

Hi Richard,

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?

Once attacked, there's no way of saving the plant (if there is a Helmithosporium infestation). Not all plants may be affected, but certainly plants where the fungus manages to penetrate the epidermis, or where there is already an existing lesion. IIn most cases it starts from the meristem, where the epidermis is not that tough.

It usually becomes active if humidity is associated with warmth. e.g. if the cacti get rain / are watered on hot days. In my experience the most exposed plants are cacti grown outdoors, especially when sunny and warm after rainfalls. I had few casualties over the years, all in mid to late summer.

Here's a topic interesting for the pictures:

http://cactusi.com/f?topic=566.0

Cheers,
Eduart

[RichardMS]

Thank you for all the different ideas. I'm starting to find these diseased cacti of interest now rather than a worry. My biggest concern was whether it was RSM but as I can see no sign of little beasts I'll rule that out (or at least assume the heavy dose of provado has eliminated them - I wonder if the white frosting I mentioined at the start was insecticide residue). I've had experience of sciarid fly in the past and remember the flies hopping around the surface and I cannot see any of them. If it is a form of fungus attack I'll just wait and see the progress and cheer myself up that those in the tray that survive will be the strong ones - if any do survive! some do not appear to have succumbed. If it is scorching I'll wait to see if new growth starts. Once again thank you for the suggestions. Helmithosporium, now theres a new one for me to fret about

[Darren S]

I've been watching this thread with interest as I've had the exact same same symptoms on some plants starting last year and can offer the following observations.

The only plants in my collection affected were seedling Lobivia/Echinopsis. The damage occurred in seedlings around 1-2 cm diameter, potted 6-8 to a pot. The problem wiped out the whole potful in the worst affected species (jajoiana and similar). Some of the others had a few survivors which have regrown this year. Some are still potfuls of mummies - not apparently dead but not growing either. The adult Lobivia/Echinopsis I have have not been affected.

There is no sign of RSM anywhere in the collection. In fact I did wonder if it was damage initially caused by the oil type insecticide I use to keep this at bay!

I had also wondered if it was the magnesium deficiency as noted by David Quail in Cactusworld as the symptoms are similar. He mentions it affecting Ariocarpus but mine seem healthy - though admittedly they are potted in a different mix. That said - adding a magnesium feed has caused greening up of my (few) older Lobivia plants and they do look much healthier.

I'm not sure I can face re-starting loads of Lobivia from seed if it is a fungal pathogen and I can expect the same again.

Does anyone know if Lobivia/Echinopsis have specific chemical demands (e.g. pH, nutrients) of which I am woefully ignorant?

[RichardMS]

Hello Darren. The worst affected seedlings for me are Rebutia (seed collected from my own plants labelled cajasensis and flavistyla) and some Echinopsis seedlings have also succumbed and with greater losses than the Rebutia cajasensis which seem to be struggling to survive better than the R. flavistyla or the Echinopsis (the Echinopsis were grown from some seed collected from a plant called 'Snowstorm' I bought at Southfield four years ago). Of those Echinopsis that have survived some are starting to put out tiny offsets that currently look healthy. I may be imagining it but some of the R. cajasensis seem to be fighting to put out new growth from their crusty caps and they all flowered this year and many have set seed - although this isn't necessarily a good sign I guess. The Rebutia look generally pale so I am wondering if they lack certain nutrients (magnesium?). Good to hear some of yours have regrown -I'm still holding out hope for mine. I notice you live near Lancaster - I'm not far away, just south of Penrith - hope we're not at the epicentre of some deadly plague!!