Aaghhh is this a fungal infection??HELP Please

[Sienna]

I had a Den that had yellowing leaves, (2nd pic) I have just been watching it, but it looks as if it's not going to make it!

Now I have noticed a very nasty looking infection on another Den (1st pic)!!

Is this an indicator of an infection in my collection??!! I have some fungicide called 'Previcure', should I treat everything as a precaution??!!

Help Please!!

Thanks

[King_of_orchid_growing:)]

It's not fungal. That's sunburn.

The light it should receive should be indirect but bright.