Orchid Culture - Questions & Answers from This Month
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!
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Yellow to Black Spots on Catasetinae
Q. I have 50 catasetinae growing in the greenhouse and 35 outside, and 2 catasetinae have an issue, mostly on the leaf tips. The leaves start to yellow ant then it turns to black spots. Is it a fungal problem, and what would I use to treat it? I have sprayed for mites as a precaution. I trimmed the tips off since it was spreading down the leaf. I can see some yellowing on another catasetinae and assume the black spots will follow.A. I'm wondering if the initial problem wasn't caused by thrips. They love the tender young catasetum leaves and leave bull's eye circles on the leaf undersides. You'll notice a spot of discoloration with a central puncture caused by the rasping mouth parts of the thrips. Then, once the puncture occurs, you can have a secondary infection causing all the yellow and brown discoloration. Whether it is fungal or bacterial is a question mark. But my best guess is the initial damage was caused by thrips, assuming you didn't see any mites on the leaf undersides. If you want to stop the secondary infection, something like copper in the cool of the evening would be effective, although the thin leaved orchids like catasetums are sensitive to it, so maybe only half strength. (Aug-25)
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Floppy Growth Habit
Q. This B. Little Stars grows like crazy but it never blooms, and the leaves bend to the point that they almost break. I grow it in full morning sun, water about 3-4 times a week and feed every other watering. Any suggestions?A. It sounds like it is not being grown in bright enough light. Brassavolas are very high light plants, as suggested by the terete leaves. You also might consider whether the plant is getting enough calcium to form strong cell walls. You can tie up the growths with bell wire using the wire hangers so they'll stand up after the leaves harden off. If your plant is healthy but doesn't bloom for you, the most common problem is insufficient light. (Aug-25)
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Yellow Base of Cattleya Growth
Q. Looking at the yellow base, the growth inside is brown. Do I have a problem?A. That new growth has rotten inside the sheath. Water cupped inside the sheath as the new growth was forming and it resulted in bacterial rot. You can just pull the new growth out gently. When you see that sheath forming a cup around the growth, you can peel it down gently so any water or condensation will drain freely. (Aug-25)