Including the example of fallen leaves

Fungus to me is a sign that you have been over watering the plant. To me, your soil looks too peaty, also looks wet. I might put in a smaller pot as well. I had one of these for years in an apartment, it grew to three feet tall, but mine looked much healthier. Are you sure it is getting enough light? Mine started with several in one pot, I thinned to the biggest one, to allow it to grow better...Good luck with yours.

Christopher

J - Your plant looks distinctly like one that's suffering from root damage and a root system that probably wouldn't be functioning normally even if it wasn't damaged. Linked to the root issue is the probability that you have a high level of soluble salts in the soil. The problem can be attributed to over-watering, but the real underlying problem is probably a soil that retains too much water, which is an inherent problem.

When you use a soil that holds a lot of excess water, you have to choose between watering correctly or watering in small sips to prevent extended periods of soggy soil. The dilemma is, if you water correctly (fully saturate the soil, using enough water so 15-20% of the total volume of water applied exits the drain hole) the soil stays soggy for too long. If you water in small sips, it sort of solves the soggy soil problem, but brings with it an entirely different problem, that being the fact that when you water in sips, ALL the salts in your fertilizer solution and in your tap water end up accumulating in the soil. These excess salts can make it impossible for the plant to absorb water and nutrients, the result is a plant starving and dying of thirst, no matter how wet the soil is. The symptoms are the same if you have soggy soil and a low level of salts in the soil because the soggy soil deprives roots of oxygen, which means they are unable to take up water efficiently, even though they are surrounded by it.

To turn your growing experience around, you need to learn how to water correctly using the soil you have chosen, or you need to learn how to manage the problems inherent in your soil choice. The easiest path is to choose a soil that makes all these problems go away and significantly increases your plants' potential for good health.

Reducing the number of plants in a pot won't make the survivor grow better. You do that by reducing the effects or eliminating limiting factors. Killing off the competition might put off for a few weeks the time at which your plant is at a point where it should be repotted, but since that is also a seasonal issue, I would say the impact of thinning isn't much of a consideration at all. You can only make progress by reducing the effects of the most limiting factors.

I'll leave you a link to something I wrote to help folks who could use a broad overview. I hope you'll read it. You should be left with the idea that soil choice is going to be a significant factor in how well your plants are able to perform. If you do end up with that feeling and want to know more about soils, I'll link you to another post that probably offers you an opportunity to take a very large step forward insofar as proficiency is concerned.

Al

Here is a link that might be useful: The overview he mentioned

Thank you for your replies! I am surprised to hear that the problem is the soil since I was using the same type of soil and the same way of watering over the years with this plant. However I did move it into the large pot so maybe somehow this is related (maybe soil does not get dry enough).
I am a bit worried to re pot it right now since it is winter time now.