Is this a case of overwatering or poor sunlight?

Hi guys,
I came from vacation and found my cactus to have yellow spots on it.I'm wondering if its a case of overwatering or poor sunlight? A few days back there was a yellow growth of fungi on the soil which i had removed.

Kindly let me know what you think about it, and how can i treat the plant.

thanks

 

How much have you been watering and what kind of humidity levels/ lighting is it being exposed to?

 

I water it once a month only, i kept in indoors though it does receive sunlight from a glass door.In july the weather changed and is a bit hotter, so maybe the plant got burnt?

 

Has the lighting in that spot changed during the time it has been there? It might need more light with the shifting position of the sun during the summer (if you have a south facing window that would be a very good choice or even outside, but if you put it outside keep an eye on the weather so it doesn't get drenched too often) - the weather becoming warmer shouldn't cause fungus to start growing in the pot unless there is an excess of moisture or lack of light. Most mushroom fungus need low or partial light to do well, so I'm guessing you need a sunnier spot!

Also if it is in one of those pots with no holes at the bottom that stores like to sell them in you should acquire a new pot for it and/or poke some holes in it if it's a plastic pot. Stores love to sell plants in those and it is bad for plants to not have a drainage system of some sort incorporated into the pot.

If your issues continue, you may want to check the soil moisture and if it is damp and smells moldy you may need to consider getting some new dirt for your plant or taking the plant out and either nuking the dirt in the mic (this works for some things but leaves your dirt hot for a while unless you then run cold water through it which you should not do for yours...don't do this with the dirt in a ceramic pot if you are impatient) or in the oven at about 160-180 degrees for 30 minutes or until bone dry. It is going to smell really weird in your kitchen if you choose to do this, but it does work fairly well. This should kill the fungus but you will need to saran wrap or bag the roots of your plant while doing this because it will be out of the pot for a while during the cooking process.

You may or may not wish to wash all of the dirt off of your roots before replanting. I have when I found that one of my plants needs this, but the ones I have done this to are not cacti. With a cactus that may be having moisture issues, I am not sure if that is a good idea or not.

Someone else may have a much better idea of how to fix this, as this is not the kind of plant that I know a whole lot on (aside from the light and moisture thing which my Christmas Cactus is teaching me but I haven't had that issue yet with it). Remember that your cactus does store water and at a certain point can survive long periods of dry, so under watering is much less of an issue than over watering. They can bounce back from over watering or excess moisture in the air if given the right conditions.