Orchid Culture - 2020 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!
Sunken Spots on Dendrobium Leaves
Q. My dendrobium has developed spots on the leaves and I'm unable to identify the cause. I have been spraying with a systemic fungicide.
A. I would say that is bacterial rather than fungal, particularly if it happened pretty quickly. Copper is a very effective bactericide but of course you can't use it on dendrobiums because they are so sensitive to it. You can pour or spray the leaves with a fresh bottle of hydrogen peroxide. There are not many great options for dendrobiums. The systemics you are using are good fungicides for the leaf spotting fungi, but not for bacterial infections.
The question is, how did the bacteria get a stronghold in the plant. Low air movement and excess leaf moisture are conditions conducive to bacterial blighting, particularly if you are growing outdoors where the plants are watered by Mother Nature, so the leaves are wet at night.
Center of Cymbidium is Dead
Q. I am located in Melbourne, Australia. When my orchids bloom mainly in our winter, I get a healthy number from each. However, there are a large amount number of dead looking growths in my pots. Should I be re-potting to remove them or leave things as they are?
A. Harry, the Cymbidium Man, advised Nigel to repot: If cymbidiums are not repotted every 3 or 4 years, the center part does tend to die and should be discarded when repotted. Potting media tends to break down and decay over time and encourages rotting of the plants as well.
Remove all rotten material
including roots. Pots should just large enough to allow for 2 years growth.
I like to divide my plants when I repot and pot two or three
good growths and a nice firm back bulb. Two years growth for a division is 2 inches between the plant and pot rim all the way around.
Not sure what material they use for potting in Oz but fine bark should be good, like the Pinus radiata bark from New Zealand.
Some of the Australian growers I know have mentioned that they use it.
Black Streaks in Flower
Q. What is causing this flower blighting? The white cattleya flower opened in perfect condition and developed the black streaks after a few days, and the pink cattleya is starting to show some streaking. These plants are being boarded and are now in a more humid environment.
A. When you get that necrotic streaking in the flower about a week after it opens, and if it seems to follow the veining in the flower, I would be very very afraid that it is virused. If it is, I would suspect it is brown necrotic streak which some believe is caused by a strain of Cymbidium Mosaic Virus and others believe is from a dual infection of CymMV and Odontoglossum Ringspot Virus. The white cattleya is almost certainly virused. The pink cattleya may just have some bacterial blighting, but if in a few days that necrotic streaking appears through the midribs, then you would be afraid of virus. Do you have any test strips to verify whether or not they are virused?
What to Do with Aerial Roots
Q. I have a small potted Vanda that I hung on the east side gutter outside in a basket about 2 months ago. When I watered her this morning, I noticed all of these tiny black spots all over her leaves. She's been getting rain water and lots of breeze. Is this fungal, bacteria, virus, or something else?
A. Those spots are pigmentation from the vanda getting nice bright light, sort of like freckles from being in the sun. The spots should be reddish purple rather than black, and they should not be raised or sunken. I think it looks great, and should be a very interesting hybrid whenever it blooms!
Ground Orchid in Container
Q. I have recently bought a ground orchid online which came in a small plastic pot, which after I transferred it in to a bigger pot. Is it absolutely necessary to plant a ground orchid in to ground only and not in the pot?
A. I don't think terrestrials have to be planted in the ground, but I think they should be potted in a peat based mix rather the coarse mix you would put an epiphyte in.
Pod with Coco Coir
Q. My phal has fungus gnats so I removed some of the media and found a bunch of mushy gunk inside the pot. There as a sort of pod filled with coco coir which seems to be contributing to the mushy gunk.
What should I do?
A. When the bark rots like that, it will also rot the roots. If it were my plant, I would get a hose end sprayer and set it on jet, turn the pot upside holding the phal in and jet away as much of the potting mix as possible, all the mix that comes away without too much pressure. Jill wrote back that she jetted all the material away and found the 'pod'. Apparently, when the growers first potted up the phal, they put the seedling in a little plastic pot filled with oasis or coconut and when the plant got larger, they just slip potted it by dropping it into a bigger pot and backfilled with bark. The inside pot will always stay too wet if you water the bark the way bark should be watered, and root rot is the inevitable result. After Jill removed it and jetted away the rest of the potting mix, she added fresh mix with a minimum of disruption to the roots.
Phal Leaf Detached from Stem
Q. I was away for the weekend, and upon my return found a very sad white Phal. She had 2 very long leaves. As I was taking the pics, one just detached seemingly from the crown. Help!
A. That looks like Collar Rot, also known as Southern Blight, one of the devastating stem rots. You can see the fungal bodies on the close up of the stem. Scroll down the SAOS website Disease page
to the Collar Rot section to read about it.
The plant is probably beyond saving.
Your only possible hope, and a slim one, is to drench the pot with some fresh hydrogen peroxide (unless you have something like Pageant) and then keep the plant on the dry side and see if a basal keiki appears. However, the tissue from which the basal keiki would grow is what is infected with the fungus, so if it were my plant, I would discard it and remove the source of inoculum from the growing area.
New Growth at Top of Pseudobulb on Miltassia
Q. This Mtssa. Chas. Marden Fitch looked like it was going to be a spike, but instead of flowers it looks like a new growth. The top of the pseudobulb also looks like it is sprouting another new growth. Any ideas?
A. I have had oncidium alliance plants form keikis from the top of the pseudobulb on some occasions, but don't believe I've ever seen one form at the end of the flower spike like yours has and like often happens with Phalaenopsis orchids. It sounds like a teenager hopped up on hormones!
Leaf Damage on Dendrobium
Q. Does the mini-dendrobium have thrip effects on it? Do I remove the infected stalks with deformed leaves and treat the rest of the plant? There are new leaves on the plant.
A. The dendrobium looks like it has mite damage, not thrips, although it is hard to tell without seeing a close up of the upper and lower leaves. The new leaves look like they are being affected by mites too, so I would say the mites are still active. They seem to affect dendrobiums and thin leaved orchids much more than they do the thick leaved orchids like cattleyas. They also thrive in dry environments, so many indoor growers have to learn how to cope with them. You first have to kill the mites on this and possibly other plants. For starters, take them to the kitchen sink and spray them with a mixture of isopropyl alcohol and dish soap, lather 'em up and wash the leaves. Then get a spray bottle of isopropyl alcohol and spray the leaf surfaces top and bottom. Make it a weekly event, perhaps part of your watering routine. You might consider treating with one of the three in one insect, disease and mite control products containing the active ingredients Imidacloprid, Tau-Fluvalinate and Tebuconazole. (Feb-20)
Maxillaria tenuifolia Bulbs are Wrinkled
Q. My Maxillaria has some new growths and roots but the pseudobulbs are wrinkled, should I leave her alone or repot?
A. That looks like it would benefit from being repotted. The mix looks worn out and the pseudobulbs are probably dehydrated from the moss breaking down. You can safely repot now because new roots are forming. Keep it in a smallish pot, it will tend to grow up and out. A basket would be great.
White Spots on Leaf
Q. What is this bug and how do I get rid of it?
A. I couldn't tell what the problem was from the pic of the top of the leaf, so I asked Humberto to send a pic of the leaf underside. The scale infestation is clearly visible on the bottom of the leaf. The first step was to spray the obvious scale with alcohol and follow up with a drench of one of the Bayer Three in One products containing imidacloprid as one of the active ingredients.
Phalaenopsis Leaf Blemish
Q. I was given a Phalaenopsis in rotting, moldy bark medium. I removed all the medium, perched it on a plastic bottle I've punched full of holes, and it's been growing in 'air' for four or five months now. I spray it twice a day with spring water, and also spray with fertilised water. The roots are NOT sitting in water. It seems healthy enough -- new roots and a leaf are emerging, and the old leaves do not look like they are yellowing. That top big leaf grew while it was with me. While it was still in bark medium, one leaf developed these mark, but they have not enlarged. Should I trim the leaf?
A. Whatever you are doing, don't change a thing! Do not worry about the bottom leaf blemish, eventually your plant will shed the leaf and you won't have to look at it anymore. It looks like something happened to it when the leaf was originally forming, but there is no active infection. Good growing!