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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Red Circular Lesions Dendrobium Virus
Red Circular Lesions Dendrobium Virus
 

Red Circular Lesions on Dendrobium

Q. I have had this Dendrobium sulcatum for 3 years and every new leaf gets spotted like this. The spots are neither sunken nor soft and they appear when the leaves begin to mature and then they spread and the leaves become papery with a rusty color. I even have cut all the leaves on all pseudobulbs, but then the leaves on the newest growth look like this. What is it and what should I do to treat it?

A. I thought the dendrobium has a viral disease, but Courtney thinks it is rust, a rarely seen microfungus. In either case, it is not curable. Read it its last rights and replace it with something you'll enjoy more.   (Sep-17)


Millipede or Centipede
Pill Bug or Sow Bug
 

Friend or Foe?

Q. Are these friends or foes?

A. What great pictures! Did you just apply some organic fertilizer? Centipedes, millipedes, pill bugs and sow bugs mostly eat dead vegetative matter but can damage new tender roots. They are not a big problem, but perhaps you should encourage them to relocate. Pick them off or pour a solution of liquid Sevin through your pots.  Here's some advice from the American Orchid Society. (Sep-17)


Bacterial Rot on Vandas
Bacterial Rot on Vandas
 

Bacterial Rot on Vandas

Q. This has been a hot and wet summer. I keep my vandas on a covered screened in porch with several fans, but with these high temperatures I have developed what I believe is a bacterial rot, which I noticed a few hours after a preventative spray with Physan. I sprayed my entire porch with 10% bleach and have not watered them in 3 days, despite the heat. I have also done several treatments of hydrogen peroxide, and today sprayed liquid copper. Do you think the vandas can be saved? Removing the infected tissue will be difficult because of the location. Is the only way to tell if I have killed it is it doesn’t continue to spread, or will it dry out, turn color etc.?

A. You're making all the right moves. Physan is okay, copper is more effective, and peroxide is great for bacterial problems. Bacterial rot in the leaf axis occurs when water pockets in there, something that is difficult to prevent when the leaves are so close together and it is so humid outside. If you tug on the leaves and they pull away from the stem, that will remove the innoculum. If the discolored area does not enlarge, the infection should not be active. More air movement, turning the plants upside down, lowering humidity, anything you can do to lessen leaf wetness will help, as will precautionary sprays of peroxide in leaf axils.   (Sep-17)


Discoloration on Plants
Discoloration on Plants
 

Discoloration on Plants

Q. I was watering my Sedirea japonica today and I noticed the discoloration of one of its leaves. My Cattleytonia Why Not also has discoloration of one of its leaves. What do you think it is and what should I do?

A. The Sedirea japonica looks great. It looks like a little bacterial brown spot at the tip of the leaf.  Just spray some peroxide on it.  As long as it doesn't enlarge, just leave the leaf alone. The Why Not looks like it has bacterial brown spot too. On younger cattleyas, it seems to be more of a problem and spreads more rapidly. Spray with hydrogen peroxide or one of the copper fungicides. Think about how to reduce leaf wetness and increase air movement if you start seeing this spread through your collection.   (Sep-17)


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