Pediocactus Knowltonii not looking too great.

[Stuart]

Has anyone any thoughts on this Pediocacatus Knowltonii ? It's been gradually looking worse during the past few months, first going from a nice green to a grey-green colour and then producing all this yucky brown growth. I would have grafted it ages ago and I take off a few offsets to graft each year. The ones I've grafted this summer still look fine in a different grenhouse but this one looks unhappy to say the least. It's quite solid, no sign of any rot. It can't be cold, although I keep the greenhouse at about 4C, in habitat it lives under snow in the winter and they are fine in an unheated greenhouse. Does that only leave a virus as the only answer?

Stuart

[fero]

It reminds me of the orange rust type markings on ortegocactus . even the epidermis is a similar blue green .
with that one they recommend the brightest spot to try control it. this is a link to "life's "ortegocactus page they are suggesting it helps it to blend in with the surrounding lichens . at least you have some good replacments.
https://www.google.com/url?sa=t&source= ... 3259518793
I would put it on a top shelf and see what happens.
also give a very close inspection ,which I'm sure you have already , just in case of wee red beasies. which it most likely isn't.

[NickHitchcock]

I have what looks like exactly the same orange growth on 2 young Matucana, they are next to 3 others, I sprayed twice with rose clear and it seems to have stopped the orange stuff from getting worse and it has not spread to the ones next to them.

[iann]

Could you bear to take a head off and dissect it? Would be good to know now if you have a systemic infection or just some skin damage. If I spotted damage like this, I'd normally suspect cold damage first, then mites, but cold damage is unlikely and it doesn't look like mites.

[Ali Baba]

The other thing you might consider is a nutrient deficiency, do you feed it with a fertiliser that contains micronutrients?