Horizontal black streaks on cattleya leaves

[MateoinLosAngeles]

Someone on Facebook was asking what this could be. The pattern confused me and made me think it might be something nutritional rather than fungal. Apparently, these black streaks appeared seemingly overnight on all growths. The grower says it's not sunburn. He waters weekly, about 60ppm N and he has hard water. Room conditions 18-25C 45% humidity. The plant is Bc. Mem vida lee 'limelight'.

Not sure about the orientation of the light, but he's a windowsill grower.

Any ideas of what this might be? Does it warrant a systemic fungicide treatment?

[estación seca]

My first thought is the plant may have been treated with something toxic that spread to that area then caused damage, or a water soluble pigment that diffused that far.

[MateoinLosAngeles]

Originally Posted by estación seca

My first thought is the plant may have been treated with something toxic that spread to that area then caused damage, or a water soluble pigment that diffused that far.

Makes me wonder if some windex got on the plant.

[Roberta]

No idea what caused it, but my "prescription" would be observation for a few days ... If it doesn't spread, then it may stay ugly but not be harmful. If it continues to change, then there's be concern. But before one treats, it's important to know what is being treated.

[Ray]

I agree with those above.

The fact that all of the discoloration is jagged and about the same place on all the leaves suggests whatever caused it was absorbed through the roots after a limited exposure.