Why is it turning brown?

[sundanz]

Im asking for a friend of mine who lives in Germany. His little green cactus turned brown after he sprayed it with insecticide. Could these be spidermites? He said he wiped it with a clothrs and the cloth turned reddish. Any help what this could be?
Thank you!

FB_IMG_1474208566034.jpg (41.85 KiB) Viewed 1203 times

[cactushobbyman]

It may have received the damage from the spray and or it had some spray left on it and was left in the sun light. Could be the insecticide used. I think people posted that oil is very bad. I would remove it from the dirt, wash it with water including the roots and let it dry and repot in fresh soil. I have a couple of fuzzy navels and they don't like bugs very much if left on a long time.

[sundanz]

Oh thank you so much!! I will let my friend know because he was very worried.

[iann]

Looks like it has/had mealies. The white things. Can't be sure from the photo. No way to spot spider mites on a photo of this scale, they're tiny. Mite damage is usually mottled. The brown discolouration on your plant doesn't look nice at all, I'd be very worried.