Orchid Culture - 2021 Questions & Answers
by Sue Bottom, from the St. Augustine Orchid Society Newsletter.
Email us with any orchid question, if we can't answer it we'll find someone who can! Send photographs too!
Cattleya Flowers Blotchy
Q. One of my Cattleya flowers looks splotchy. It looks questionable to me, could this be because of a virus or disease?
A. That sure looks like color break on that orchid, which would suggest Odontoglossum Ringspot Virus or ORSV. It's a shame, cause it's a beautiful flower otherwise. Kiss it goodbye.
Mottled Cattleya Leaves
Q. I was reading about fungal problems and noticed that many of my cattleyas have leaves that are becoming mottled. I have attached pictures for examples of what I am seeing. I am concerned that most of my cattleya plants are diseased.
A. Leaf mottling is typically caused by one of three things:
1 - Scale, turn the leaf over to make sure you don't have the dreaded boisduval scale on your cattleya.
2 - Fungal Infection, turn the leaf over and see if you see tiny dots or blotches of dots, the spores.
3 - Magnesium deficiency, which is what I suspect you have and what I had for many years.
Our water is very magnesium deficient and most fertilizers do not contain magnesium. Magnesium is an essential component of chlorophyll, that's what turns the leaves green. During extremes of heat and cold, the chlorophyll can degrade and give you that mottled appearance. I add magnesium sulfate, Epsom salts, to my fertilizer solution. Some people apply it in the spring and fall, others apply it monthly. I give mine Epsom salts every time I fertilize, which is every time I water. If you use 1/4 tsp/gal fertilizer, add 1/4 tsp/gal Epsom salts at the same time. The only caveat is you can't mix Epsom salts with a CalMag fertilizer, but with a CalMag fertilizer you shouldn't have to add supplemental magnesium.
Tiny Castings from Cork Mount
Q. I have a giant Dinema polybulbon mounted on cork. It was outside all summer, but now that it’s in the greenhouse, I realize that the cork is inhabited by something that is creating copious tiny castings. I’ve got a new piece of cork, and I guess I can re-mount the plant, but I’m worried that the critters will move into the new cork with the plant, and also move into my other mounts.
I found info about steaming and baking the cork, but I can’t do that with the plants on it!
A. That looks like frass from dry wood termites. You might try soaking the mount for an hour in a strong solution of imidacloprid, say double strength. That's not the strength they use to treat foundations, etc. for termites, but it's probably as strong as you'd want to try with your orchids. I don't think the termites will go after your plants, but of course you don't really want a colony of termites anywhere close to your house.