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.

Should I add any calcium?

I think your water has enough. Others here use a calcium/magnesium supplement routinely.

Thank you so much for your help! I will be treating this orchid then for bacterial/fungal issues and adding Magnesium.

Probably wouldn't hurt to treat my entire collection would it? Dendrobiums can't have physan, correct? I have both physan and phyton available to me

I think it's a bad idea to treat unless problems are seen. Fungicides also kill beneficial organisms which may help control pathogens. It's the same reason doctors don't want to treat people preventatively with antibiotics; this selects for resistant organisms that might be harder to treat.

Instead of treating an entire collection with fungicides or bactericides I would treat the sick plants, and use a regular preventative treatment of beneficial organisms. Ray sells one you can find it on his Web site firstrays.com .

Most diseases are better prevented than treated. This involves lots of air flow, proper temperatures, humidity no higher than necessary, and not splashing water among plants.