Growing black patches on cattleya leaves

[My Green Pets]

It started with four puncture wounds that looked as if a kitten had taken a bite (very possible). There seemed to be slime trails around the punctures, causing me to wander about snails or slugs.

Black patches slowly surrounded the punctures and began to spread.

I removed the infected part today. I thought it was unusual that the black did not penetrate both sides of the leaf.





Now, there are black patches developing at the tip of another leaf. Did this spread? Will this spread until it consumes the plant if I don't cut this off? Any idea what I am dealing with?

[Leafmite]

Any time there is a puncture or cut to a leaf, there is the opportunity for bacteria or fungus to enter and spread (similar to when our own skin is punctured or cut). The same goes for when roots are damaged during a potting (that is why it is often helpful to keep the roots dry for a day or two so that they might heal). I would remove anything damaged and disinfect with isopropyl alcohol.

[estación seca]

I agree with the above, but it looks like two different things to me. And I have noticed Cattleyas are more susceptible to things when the seasons are changing and they are cooler than before.

[My Green Pets]

I submerged the entire plant, pot, leaves and all, in a solution of tap water and ammonium salts similar to Physan 20 for fifteen minutes or so.

i am tempted to remove the discolored portion of the second infected leaf, but will wait a day or so first to see if it will stop.

[estación seca]

If it's a fungal or bacterial disease, the black areas are caused by organisms growing in the tissue inside the leaf. External treatments will have no effect. A systemic fungicide or bacterial antibiotic would be necessary. Once the black area appears, it's too late to get systemic chemicals into the affected leaf, since it takes some time.

Often infected areas don't turn black for some time. The organisms may be spreading in good tissue that still looks green. This is why people recommend cutting off large margins when excising bad areas.

[silken]

I would be tempted to remove that other black part on the leaf as well. Maybe a treatment with Cleary's which is a systemic fungicide.