Orchid Culture - Questions & Answers from This Month

Bottom Phal Leaves Yellowing

Q. Late last summer I learned the hard way that afternoon direct sunlight can seriously damage orchid leaves. As the attached photos show, two of the bottom leaves of this pretty healthy orchid got severely sun-damaged. I thought it best to leave both damaged leaves on the plant until they fall off, but they are still in place now 7-8 months later. Is it best to carefully cut them off, or should I continue to wait until they fall off?
A. I don't think those leaves are sunburned at all. Sunburn, when it happens, occurs on the highest point of the leaf where the light hits the leaf at the most direct angle, perpendicular to the leaf. What you're seeing on your healthy phal is that the lower leaves are dying off, to be replaced by new upper leaves. If there is anything that is concerning, it is that the newest leaf seems smaller than the other leaves, but of course it may still be growing and filling out and it may still grow the same size as the others. If it doesn't, however, it suggests that the plant is not getting something that it was getting before when it grew the other leaves. Could be it is receiving lesser light, could be the bark mix is starting to degrade so the roots are beginning to suffocate, could be it is not receiving the nutrients it was receiving before? To answer your questions, don't cut the leaves, they are not diseased and do not pose a risk to the plant. As they yellow and die, the plant will reabsorb nutrients in the leaves to fuel the new leaves. When they can be removed with a gentle tug, you can remove them.   (Jul-24)

Catasetum Lip Didn't Rorate Downward

Q. Is the labellum of this catasetum yellow and sepals and petals the brown? Why did the lip not twist downward like my cattleyas do?
A. The catasetum lip is yellow and the sepals and petals brown. The catasetum probably didn't rotate the way you wanted because you tried to stake it to go upright, rather than allow it to be pendent. If it had been allowed to drape over the pot, the lips would have been oriented correctly, perpendicular to the flower spike. If you don't have it hanging, you can always put the pot on top of another pot to allow the flower spike to grow more normally.   (Jul-24)

Black Leaves on Cattleya

Q. Both of these orchids have this black disease, which travels through the leaf, top to bottom and in on case it completely contaminated the whole leaf and looks like it will do the same on other leaves that are just blackening. Do you know the diagnosis and how to treat it?
A. Some people would call that black rot, implying that it is the disease caused by one of the water molds. I think it is black and it is a rot, but I suspect it is caused by bacteria rather than the water molds. Completely remove the leaves, and spray with either a fresh bottle of hydrogen peroxide or something containing copper. I'm guessing this happened after the plants had lots of leaf wetness? One thing you can try after storms, and particularly after a tropical storm with lots of gray, wet weather is to spray the leafs with something like Consan/physan/pool algaecide. You can mix it up in a little hose end sprayer and just douse everything after the rain passes, that'll help keep the bacteria at bay. The true black rot that infects our cattleyas usually happens more in the July/August time period when the humidity is way high, and the water molds infect the plants usually from the roots up into the rhizome and then pseudobulbs. I do bimonthly drenches with Aliette/Subdue starting in May to try to keep black rot away, and also keep plants drier in the high humidity months.   (Jul-24)