Why is my Cactus Turning Yellow from the Top

[Kelly_CactusMom]

My cactus started turning a pale yellow color and it is growing from the top down towards the base. He's currently in a south facing window and has been getting watered about once per week. What could be causing this and what should I do to save him?

 

[Kelly_CactusMom]

He also has some white spots (see picture below). Could this mean there's a pest problem?

 

[zigs]

Over watering, once a month would be better

 

[Daren]

He also has some white spots (see picture below). Could this mean there's a pest problem?

Small white spots if fluffy looking will be Mealy Bugs Which can be treated easily with a Cotton Bud dipped in meth's and carefully applied to the white spots. The other problem is probably as Zig says Just over watering. Which can kill a Cactus Quicker than Any Mealy bug.

 

[Larisa]

Perhaps this is Dry rot (the causative agent of the fungus Phoma rostrupii). If I'm right, then it's impossible to fix it.

 

[Tjohn]

Larisa is right. Sorry, but your poor cactus is losing the battle. Sometimes cutting it back to the healthy part will encourage more arms to develop, if you can catch it soon enough.

 

[Kelly_CactusMom]

Larisa is right. Sorry, but your poor cactus is losing the battle. Sometimes cutting it back to the healthy part will encourage more arms to develop, if you can catch it soon enough.

So, you would recommend cutting all the "bad" parts off to try and give it a chance to keep going?

 

[Tjohn]

So, you would recommend cutting all the "bad" parts off to try and give it a chance to keep going?

Yes, I would. It has worked with a couple of mine, but it is an extreme measure and not guaranteed.