Black spot and preventive care
 

I have two Catts which have developed some small black spots, as shown in pic.

C.hyb.jpg - Google Drive

Some info I read stated that it is caused by bacteria landing on the leaf via water dripping from another plant, while others stated that it was likely mechanical damage.

Both could have likely happened, given that they are situated in a wire shelf in a tent.

If bacterial, should I be treating it/they and other plants?

I also didn't know if anything like preventive treatments were a part of anyone's culture. The only measures against pests/disease I have in my culture at the moment are a bacteriostatic for the humidifier reservoir, sanitizing tools & potting area, cleaning up puddled water from the mounts, and a sundew which has eliminated some fungus gnats.

I've had good results preventing black spot by using a biofungicide or plant probiotic mixed with a non-ionic surfactant like coco-wet (i avoid using dish soap because its surfactant properties are pH dependent). Do not use chlorinated water and foliar spray all surfaces of the plant (pH to 5.5-6.5). Repeat 3 times about a week apart and monitor the plant- lots of times this will only prevent new spots from forming. But these products will give you long term protection and keep the spots from getting worse as long as they are used every few months.

Ray sells quantum total which is a consortium of bacterial species as well as southern-ag's biofungicide (Bacillus amyloliquefaciens).

quantum total
Bio-fungicide

I like using Bacillus sp. because the bacteria produce anti-fungal lipopeptides that are remarkably effective on a wide range of pathogens. Even better, since these products are produced by fermentation, high levels of these compounds build up in the solution. When you combine this with a surfactant you get the activity of these compounds in the solution, and then long term protection after you establish these bacteria on and in your plant. If its really bad maybe you can use some systemic antibacterial/anti-fungal but the added bonus of using microbes is that many of them also produce plant growth promoting substances so you end up with more vigorous plants as well.

Thank you! I have Quantum already, and will incorporate that procedure into my culture. I didn't know it had use as a biofungicide.

This also happens a lot when bugs bite a leaf, then a zone of tissue around the bite dies. Fungus is very rare with relative humidity regularly around 50%. This helps people figure out what is happening.

yes it has multiple species of Bacillus that will produce anti-fungal compounds. do not spray your orchids with the surfactant if you expect leaf temperatures or ambient temperatures above 75/80 degrees as it can damage your plants. spray early in the morning as possible or in the evening.