What are flat, whitish spots and brownish, slightly raised spots appearing on succulents and cactus
White spots on some succulents and brown slightly raised spots on others. I cannot see any insect that might be making them. Are the plants diseased? How to cure?
It sounds like scale. This article should help identify: https://www.gardeningknowhow.com/plant-problems/pests/scale-bug-how-to-control-plant-scale.htm
In addition to insecticides, both systemic and contact, I've used water pressure to help control scale. If the skin of the cactus or succulent is reasonably tough, I've applied water through a shut-off valve that knocks the scale from the plant. Be careful that the stream of water isn't so hard that it damages the plant. After getting scale from the plant, I usually use both contact and systemic insecticides. In the case of scale, my theory is, "Either kill the scale or kill the plant." Sometimes, if the infestation isn't too large, a toothbrush works well. And, remember, there are several varieties of scale. Color can indicate variety or maturity of insect.