Big areas that seem like dryness appeared on the stem of my cactus over a month ago.
It’s been in the same location on the window top for all it’s life and been getting the same amount of sun and water. In the past few weeks I reduced the amount of water.
See picture attached.
Many thanks for the help on behalf of both of us :)
Thanks for providing such a clear photo of the dry spots on your cactus. Brown spots on cactus are typically caused by environmental issues. In your case, the issue could be sunburn. As you’ve noted, the location of your cactus hasn’t changed. Has something outside changed causing more light to suddenly be received by the cactus through your window? The condition is caused by a sudden increase in light. A simple change such as turning the plant to a side that had previously not been exposed to bright light could be sufficient to cause damage. Cactus can adjust to an increase in light by being exposed to it gradually such as moving your cactus further away from the window and gradually moving it back to the original spot. A good practice is to turn your houseplants a quarter turn whenever you water them.
There is fungal disease called sunscald which effects cactus and can look similar to sunburn. There is no treatment for this issue. Fungal diseases are promoted by over watering. It sounds like you a careful about your watering. I’m including below a link to our guide on growing cactus. It recommends holding back on watering in the fall as daylight hours get shorter and through the winter only watering enough to keep the plant from shrivelling.
While the dry areas are unsightly, they are largely cosmetic so your cactus should continue to thrive.