Possible disease on cattleyas

[ArronOB]

Hi. I have several Cattleya hybrid plants with a disease (I think) that I can’t identify.

The symptoms are:

Yellow, randomly shaped patches on the top surface of the leaf.

On the bottom surface of the leaf, and corresponding fairly exactly to where the yellow patches are, there are minute black spots. Like patches of dusty black spots.

The leaves feel normal and are not dried out or wrinkled.

The plant generally looks healthy if the yellow patches are overlooked.

Neither the black spots nor the yellow patches are discernible to the touch.

I looked at the black spots under magnification and they don’t reveal any particular characteristics (ie they don’t appear to be fruiting bodies), just tiny black marks.

On any affected plant, most of the older leaves have the symptoms.

I think about three plants are afflicted and it doesn’t seem to be spreading, which is surprising as I keep them close together with others and don’t limit splashing when watering or engage in other cultural practices that might limit disease spread.

The photos are of the same leaf, upper and lower surfaces. Ignore the fairly large chunks taken out by some passing insect.

I’m very worried about this one, so any advice appreciated.

Thanks
Arron

[signin1234]

I don't know but good luck. What's your fertilization routine like?

[ArronOB]

Originally Posted by signin1234

I don't know but good luck. What's your fertilization routine like?

I fertilise with ‘orchid fertiliser’ about once every two weeks in summer and maybe every 6 weeks in winter.

Why? What’s the connection ?

[Ray]

When I first moved to NC, I did a lot of watering with my tap water, and I started seeing similar pale patches in some of the leaves. A later analysis showed my water contained no magnesium, so I started supplementing with Epsom Salts, and it has gone away.

Can’t help with the underside appearance. Sorry.

[Dollythehun]

I have a few plants like this. Ray is spot on. As to the undersides, that most likely is some kind of mechanical damage.

Leafmite told me to use crushed eggshells in my mix, which I have done, and I also use Cal mag once a month. But epsom salts will kick start them and is cheaper.

[WaterWitchin]

Yup, I also vote for the kick-start with epsom salts. Are you using tap water or RO or rainwater? If either of the latter two, check your "orchid fertilizer" and make sure there's a cal-mag supplement. Or continue to use the epsom.

And can't tell from the picture, but are those little brown spots on underside of leaf possibly scale?

[ArronOB]

Thanks for the replies

It does make sense that it’s not an infection. It isn’t behaving like anything infectious.

This is the latest local water analysis

https://cdn.centralcoast.nsw.gov.au/...rt_-_final.pdf

The figure for magnesium is 4.6mg/l . Does that sound like a lot or a little ?

Anyway,it’s easy to try some Epsom salts as the next step.

Cheers
Arron

[SouthPark]

Hi Arron - I use a product called B.A.M.

Click Here

And Click Here

I apply it once a month - (usually 2 weeks after I apply my regular orchid fertiliser). It comes in a bottle with 1 litre of BAM in it.

I just choose something like the 'supplement feeding' option, which says 80 ml BAM per 10 litre water, which is 40 ml per 5 litre, or 8 ml BAM per litre of water. And then I just use one-third of this concentration.

[Ray]

Originally Posted by ArronOB

The figure for magnesium is 4.6mg/l . Does that sound like a lot or a little ?

Very little - 4.6 ppm. As a reference, MSU RO, when used at 125 ppm N, gives 71 ppm Mg.

[rbarata]

My Laelia tenebrosa also had this issue (same symptoms) and I assumed it was Mg deficiency.
Watered it with Epson salts and, while the leaves never recovered from those "stains", the new ones grow without it.
I was advised to never water with fertilizer and Epson salts together. I used them for a month, then one week without fert or salts, then resumed fertilization.

Some info here.