Brown filaments and tiny sponts on the undersides of leaves

[Russ1992]

Hey Slipper fam
I unfortunately have an issue affecting a few of my paphs. (please see photos)
As you can see there is some weird brown spotting/discoloration on the underside of my leaves. The issue is usually the most problematic on the lowest leaf with each newer leaf being less affected than the last. As time goes on the lesions or marks become more pronounced resulting in sickly yellow leaves with brown undersides. Oddly, one or a few individuals have this issue while being surrounded by seemingly healthy-looking paphs. I'm not sure the the issue is simply fungal, pest-related or a combination of both.

For a long time I thought the issue was simply spider mites, but I haven't been able to see any webbing on these plants and furthermore I have been treating them with Azamax, soap, and alcohol to the undersides weekly but the problem seems to persist and slowly worsen regardless.

New growths seem to be spared in all cases except for the most badly affected plant (last photo).
Any help would be much appreciated. Thanks everyone and Happy Holidays!

 

[DirGo]

A very interesting question. I would certainly like to read any further comments.
My line of thinking was also on mites, but I am certainly not the expert in this field. Maybe you have some level of control, and the infection needs to be worse before you start to see the webs? I did not know Azamax, but I read it is an Azadirachtin-Based miticide extracted from neem seeds and works systematic. This should work.
In absence of any better advice, maybe you could consider another systematic miticide with a different active ingredient to exclude any resistance your mites have versus the Azadirachtin?

 

[Roth]

Nutrition problem... I saw that on large scale in Maudiae types when the pH of the potting mix was too low. It is not a disease or a pest.

 

[Ray]

Those leaves certainly are pale.

 

[Russ1992]

@Roth Xavier, I do believe you are right good sir.

I purchased a new PH test kit from General Hydroponics Link which appears to be more accurate as it indicated my solutions have been right around 5 instead of 6-6.5 as my PH pen and strips were saying. I have JUST started to adjust the PH to around 6.5 and this along with a thorough monthly flush seems to be reversing the yellowing slowly. I suppose this is a lesson to never assume the one or two tools you have on hand will be accurate.

I should have stated that ALL of my plants are overly yellow (see the image of a full tray) when compared to when I first got them or when looking at other references online; some just developed brown specs on the underside over time.

Will see if adjusting the PH up will stop the speckling from advancing further into new leaves but moreover hopefully it reverses the yellowing, and widespread stunting I'm encountering.

 

[Russ1992]

A very interesting question. I would certainly like to read any further comments.
My line of thinking was also on mites, but I am certainly not the expert in this field. Maybe you have some level of control, and the infection needs to be worse before you start to see the webs? I did not know Azamax, but I read it is an Azadirachtin-Based miticide extracted from neem seeds and works systematic. This should work.
In absence of any better advice, maybe you could consider another systematic miticide with a different active ingredient to exclude any resistance your mites have versus the Azadirachtin?

Thank you for the reply DirGo I have to say I try to stay away from heavy chemicals if possible. I do think however at this point that Xavier and Ray are right for a few main reasons.

1. The damage doesn't exactly resemble mite damage that I have seen in the past, nor do I see any webs or mites under a microscope.
2. Whenever I have used Azamax in the past it has worked very well and rather swiftly. For it to not work for months on these plants tells me I'm probably treating the wrong issue.
3. All my plants are too yellow with stunting all around. If watering frequency and airflow in the mix is correct (plus my mixes are never more than a year old across the board) then this tells me I have a nutrition or salt problem. This has been frustrating since supplementing with more fertilizer, rotating fertilizers/additives, or using distilled water all failed to correct the problem. I can't think of anything else than adjusting the PH. Interested to see if others have had something like this in the past happen to them.