Orchid Culture Questions and Answers
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Orchid Culture - Questions & Answers from This Month
by Sue Bottom, from the St. Augustine Orchid Society Newsletter
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Brown Spots on Phal Roots
 

Brown Spots on Phal Roots

Q. I have been using the "weakly, weekly" fertilizing routine with an MSU formula and flush the pots every 4th week. However, I have noticed that the aerial roots sometimes develop brownish spots which are rather unsightly, but also worries me that they are getting fertilizer burn. Is there a way to prevent this from happening?  

A. I'm assuming you don't have a water softener, so you don't have to worry that the sodium from the softener is negatively affecting your orchids. I don't like the brown markings on the roots, put a little sphagnum moss over them to help keep them moist and prevent salts from precipitating.   (Mar-18)


Lower Leaves Wilting on Rhyncostylis
 

Lower Leaves Wilting on Rhyncostylis

Q. This Rhynchostylis arrived about a month ago and I grow it in a southwest window. The lower leaves are wilting (they had the black areas when I bought it).   I water it everyday and once a week I fertilize it with 1/4 strength MSU. What is wrong and what can I do?  

A. My guess would be the indoor humidity does not match the greenhouse humidity in which it was likely raised, and the dehydration and yellowing of the lower leaves is the result. If you have access to live spanish moss, you could drape it around the roots to help raise the local humidity. Growing vandaceous orchids indoors can be a challenge with the low humidity indoors from artificial heating and cooling systems.   (Mar-18)


Progressive Rot on Pseudobulbs
 

Progressive Rot on Pseudobulbs

Q. This Laelia rubescens has a disease. I suspect Phytophthora or virus.  

A. Your plants don't look virused. The Laelia rubescens could have black rot, if the rot is moving quickly and is soft and has a distinct nasty odor. If it is more hard than soft and progresses very slowly from older to younger sections of the plant, it is more likely to be Rhizoctonia. Knock it out of the pot and look at the roots, if the oldest pseudobulbs have no roots, it's Rhizoctonia solani that has built up to toxic levels in the pot and caused the root rot. You'll have to cut the plant up until you find healthy tissue, using a sterile tool for each cut, and then pot up in fresh potting media. It should recover, you can pour a systemic fungicide effective on Rhizoctonia through the pot if you have some, and maybe some root stimulator like seaweed to get it growing again.   (Mar-18)


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