BCSS - Forum

Three Mammillarias have started to grow without forming spines on their tubercles. Sun damage or virus? These pics show June growth:

This may well be Red Spider Mite again.
Perhaps you should check your plants with a reasonably powerful magnifying glass. RSM are tiny reddish brown/honey coloured bugs. When you have a severe infestation you may see a very fine webbing - like a spider's - covering the plants or strung across gaps between plants.

The reason I suggest RSM is that the new growth doesn't look a healthy colour. It looks dryish, like it has been recently infested by RSM. Eventually the epidermis will look like your other pics posted.

Thank you. Last week I sprayed all my collection with the local garden centre Bug Clear Ultra, which states it includes red spider mite control. Spraying again next weekend. Tempted to use language here which I shouldn't use. Hoping no more plants succomb.

I question whether this is red spider damage, tru they go for the softest tissue i.e. the new growth, but I cannot see any actual damage.

I wonder what you grow your plants in and where they are kept? It looks more like a deficiency to me.

Suzanne Mace

Could it be lack of sunlight or overfeeding?

I think it is fairly fresh RSM damage, before the scarring becomes apparent like the plants in the other post. In my experience, the pallid green without any glossiness to the surface is a key indicator.
In this instance the the treatment given has sorted out the mites and now the plant is beginning to grow.
I suppose time will tell.

Topsy, I grow the plants in 50% grit, 50% John Innes2 (changing now to 3). The plants are grown indoors on a south window with many days outside in direct sun when the weather permits. There is some virus around the garden which has affected lilac trees, clematis, snapdragons (last year) and blackberry plants.

David48 wrote:Topsy, I grow the plants in 50% grit, 50% John Innes2 (changing now to 3). The plants are grown indoors on a south window with many days outside in direct sun when the weather permits. There is some virus around the garden which has affected lilac trees, clematis, snapdragons (last year) and blackberry plants.

It's possible that the high level of UV light from direct sunlight has damaged the young & vulnerable epidermis. If the plant was outside in the very hot sunny conditions a couple of weeks ago, it could have been a factor. My experience of RSM is that it causes a pale callous to form over new growth and yours doesn't seem typical of that.

An update is that two more Mammillarias have also now succumbed, this would be after spraying several weeks ago. I don't think it is nutrient deficiency, I have watered fortnightly with a fertiliser.

Maybe such frequent use of fertiliser is the culprit? Provided your plants are potted in a decent potting mix such as JI, they shouldn't need to be fed every two weeks. Try no fertiliser for a while and see if there is any improvement.