Wilsonara firecat king snake spotting on leaves and streaking
 

My Wilsonara firecat king snake has had some yellow spotting on the back of the leaves on the new growths. Well, now there is streaking down one of the leaves. Not sure what it could be. I have read fungal and viral both can look this way. What are your thoughts?

What are the growing conditions?

Growing under timed grow lights about 12-13 hours a day, humidity in the 70s-80s and about 74 degrees F during the day and 68 at night. There is a fan constantly running the area it is in to help with air movement.

The many spots look like bacterial or fungal disease. The black reminds me of acidovorax or Pseudomonas infection. The yellowed leaf looks like nutritional deficiency.

Go to the diseases page of the St Augustine Orchid Society Web site, and read about bacterial brown spot. It discusses treatment. Prevention involves good air circulation, which you have, avoidance of wetting the leaves and reducing ambient humidity. I think your plants would grow fine at 50%-60% relative humidity with less risk of infection.

How are you fertilizing? Yellowing can be caused by nitrogen, magnesium or iron deficiency. The last is uncommon in epiphytes.

It's not causing these problems, but you don't need more than 10-12 hours of light.

For feeding, I have been using MSU fertilizer but just switched to Jack's Classic all purpose. It's 20-20-20. I typically water weakly, every other watering which evens out to about every 1-2 weeks. I typically add in a little iron also because I also water my violets with it and they were deficient in iron.

How much fertilizer are you mixing in how much water?

When I was using MSU, I was mixing 1/2 tsp per gallon, the Jack's Classic (I used it for the first time yesterday) I mixed 1/2 tsp per 2 gallons.

What kind of water are you using? You're not fertilizing much, and there isn't a large amount of magnesium in those fertilizers.

Oncidiums aren't supposed to go dry. A week between watering is a fairly long interval, though perhaps your high relative humidity means they aren't drying out completely even with relatively infrequent watering.

I fertilize every 1-2 weeks, I water at least twice a week. I typically use just the city tap water. I am attaching the water quality report.....the water here is fairly good water.

Your water is lowish in dissolved minerals, but not too low. I would still suggest a magnesium supplement. Epsom salts provide magnesium but not calcium. You could add a teaspoon per gallon.