Orchid Culture - 2021 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!
Black Stains on Cattleya Leaf Undersides
Q. I pride myself in having clean leaves but some Cattleya species like violacea or tigrina (and others) seem to get black stains on the undersides of their leaves.
Am I doing something wrong? If not, can it be prevented or is just Mother Nature?
A. That sure looks like fungal spores on the leaf underside. The upper surface of the leaf has chlorotic blotching matching the location of sporing underneath.
There are several leaf spotting fungi that infect cattleyas. When you repot/remount, you can cut away infected tissue. In the meantime, you can spray fungicides like Pageant, Thiomyl/Banrot or Daconil to help prevent the spores from spreading the disease.
How Do You Pot Up Dendrobium Keiki
Q. Can you tell me how to put this dendrobium keiki in another pot?
A. You can cut the cane an inch away from the keikis on either side, soak the roots to soften them and then situate the keiki roots in the pot. You can backfill with potting mix around the roots immediately, or better yet, just add a handful each week so the aerial roots will branch and become acclimated to the mix. It looks like you might have mites on the upper keiki, and the lower keiki may have succumbed to mites, so you'll have to treat for that. The keikis are probably the future of that plant, the mother plant is probably not going to survive.
Divide or Pot Up Cattleya
Q. This is one of my favorite orchids, Blc. Volcano Spring. I want to divide it when it’s finished blooming. It has about 30 pseudobulbs. How many divisions should I try to realize?
A. You could probably get many divisions if you wanted to, but the cattleya has such a short internode distance that you can have many pseudobulbs close together in the pot. You should think about growing it up to specimen size. Select a pot that is an inch or two bigger all around to drop the plant into, once you remove all the decaying old media. If the older leaves were blighted, I'd say cut away the older growths, but those leaves all look pretty good. Unless you want to separate it, think about putting it into a larger pot with fresh potting mix.
Dendrochilum with Brownish Discoloration
Q. This mounted Dendrochilum glumaceum has leaf changes that began about 3 months ago on two leaves which I removed. It is now on older and some younger leaves, mostly the undersides but then progresses to the tops; the pseudobulbs are not affected.
It receives infrequent overhead water, being watered every other day after the moss has dried and has good air circ. I sprayed with hydrogen peroxide twice early on, but nothing else since.
A. That looks and sounds like a fungal infection, rather than bacterial or viral. It sounds like one of the leaf spotting fungi. There are common fungal leafspot diseases in ornamentals from Alternaria, Cercospora,
Septoria, and Phyllosticta. Something like Pageant or Heritage are often recommended for leaf spotting fungi.
It sounds like you are doing everything right culturally. I wonder whether this cultivar is just more susceptible to the fungus. If this is the case, you can accept it, try routine applications of one of the fungicides, or perhaps consider the radical option to completely sanitize the plant. Remove each and every leaf that shows signs of the disease to the top of the pseudobulb. The hope would be to remove all the spores from the area so the fungus is stopped. Then, apply a protective spray on the plant, cross your fingers and hope for new growth and leaves. (May-21)
Black Diamond Shaped Lesion on Vanda
Q. Is this Thai disease on my vanda? Is Physan good for treatment, or is there something better?
A. It looks like the fungal infection Guignardia, or Thai disease. Run your fingers across the lesion and if it feels like sandpaper, that's what it is. If so, maybe invest in some Thiomyl, otherwise known as Cleary's 3336, with the active ingredient Thiophanate Methyl. Monthly preventative sprays are recommended in Motes' vanda book. (May-21)
Green Pointy Bumps on Cattleya Leaf
Q. My catt has some bumps and strange growths, should I be worried?
A. I don't think it's anything to worry about. I've had what looks like extra tissue growing on the upper side of my cattleyas from time to time. I don't think it's edema, which is a blister that forms on a fully developed leaf. This is some sort of mutated tissue that forms as the leaf is developing. Courtney thinks it is a genetic issue, probably triggered by environmental conditions. Hopefully, the next leaf will be normal. (May-21)
White Stuff on Phalaenopsis
Q. I think this damage on my phal is due to mealy bugs but I never see any critters. I see white stuff on the under side of leaves and in crotches. Could it be something else?
A. Those are definitely mealybugs, and your phal has them bad. Drench them with the imidacloprid product, which means pour the solution through the pot to wet the roots, which will take up the chemical and move it to where the mealybugs are feeding. At a concentration of 1.47%, the label rate is 6 teaspoons per gallon, you might even consider using it double strength the first time to knock out the infestation. You might also consider drenching all your surrounding plants in case the mealybugs have moved into them.
Yellow Spots on Cattleya
Q. I have noticed yellowing spots on my cattleya orchids recently along with a few spots on the back of some leaves. Does this look like scale to you?
I have a systemic insect control liquid that I use on other plants with the active ingredient acephate. Can I use this on scale?
A. That is scale alright. Acephate is the active ingredient in Orthene, and can be used on your orchids to control scale. Good luck!
Longitudinal Streaking in Cattleya
Q. These are leaves from a Blc. Lily Marie Almas a bifoliate cattleya. It receives various fungicides throughout the year but I am concerned it is a fungus. The marks are not as dark as they appear in the photos as I was trying to highlight them with backlighting so you could see the areas better. Please let me know if I should remove any leaves or treat with any chemicals.
A. It's hard to tell, but my best guess would be it is bacterial rather than fungal, particularly if it happened quickly? The longitudinal streaking makes me think of bacterial brown spot, which in younger, tender cattleya leaves looks like that. The backlit photo really shows the infection well. If you have some copper, you can spray the leaves, although the bacterial problem is inside the leaf. As long as the discoloration doesn't get larger, the leaves will still help support the plant. On the other hand, if you don't want to look at that discoloration anymore, you can remove the leaf. The plant looks nice and healthy, it should be a minor setback.
Droopy Phal Leaves
Q. This is a Phal. Yaphon Green Batman that seems okay except for the drooping. I use reverse osmosis water with Epsom salts when watering. Any suggestions?
A. Perhaps you should knock it out of the pot and take a look at the roots. I'd guess there is a root problem. Norman's Orchids packs the sphagnum very very tight on their phals, so even when the top may feel dryish, the bottom of the pot is still wet, so it is very easy to overwater them. Knock it out of the pot and check the roots, that will guide your course of action.
Q. I am having a problem with the flowers of some of my dendrobiums.
The buds are damaged. They either fall off or if they develop
into flowers the petals are small, deformed and damaged.
I don't really know if it is a fungal disease or caused by pests.
A. Just looking at the flowers, you couldn't rule out bacterial blighting, but my guess would be thrips based on the damage you are seeing on the buds. Thrips are very difficult to control. They crawl into the buds and chew on them long before the flower is ready to open. If this is a persistent problem, you can spray the buds and flowers once or twice a week with Orthene to prevent the damage, or drench the plants every 6 weeks or so with Orthene. There's more information here.
Catasetum Bulb Rotting
Q. I got my first 2 Catasetums last year and am noticing something strange on both. There are dark brown, slightly sunken and a bit sticky, spots on a couple of older pseudobulbs.
This only developed after I stopped watering them for their winter rest so I’m not inclined to think it is rot. The newest bulbs are still quite plump and I have a new growth just starting on one. Should I be concerned about these spots?
A. Yes, it is rot. Feel the bulb, it probably feels pretty soft compared to the one next to it. This is not an aggresive rot like black rot in cattleyas. It is slow moving and you can just cut away the older bulbs when you repot, which you should consider doing now as the new green growth is emerging.
Green Blotches on Phal Leaf
Q. Are the green blotches on the phal leaf something I should be concerned with, they are more pronounced on the keiki than the mother plant. The plants were moved into the greenhouse when cool weather arrived.
A. My best guess would be some cold water damage, either from overnight condensation dripping on the leaves or cold water from the tap. Check the temperature of the water coming out of the hose and see how close to 70F it is, the water should be within 5 to 10 degrees of the air temperature. The keiki leaves are likely more tender than the Mom's leaves, and more sensitive to cold water damage that can cause mesophyll cell collapse.
Pool Algaecide Strengths
Q. I have a question regarding pool algaecide versus Physan. Is the product in the photo appropriate and what rate per gal should I use?
A. Physan, which contains 20% quaternary ammonium compounds, recommends 1 tsp/gal as a spray. Your product appears to contain 30%, so you would use 2/3 strength, or 2/3 tsp/gal.
Leaf Damage on Phalaenopsis
Q. This phal was with all my others on the north face of a wooden fence. Any ideas what caused this damage?
A. My guess would be the new tender leaves were damaged somehow while they were forming and the scars simply enlarged as the leaves got larger. Perhaps it was mechanical damage, or perhaps water in the crown. The other leaves look great. (Feb-21)
Cattleya Flowers Blotchy
Q. One of my Cattleya flowers looks splotchy. It looks questionable to me, could this be because of a virus or disease?
A. That sure looks like color break on that orchid, which would suggest Odontoglossum Ringspot Virus or ORSV. It's a shame, cause it's a beautiful flower otherwise. Kiss it goodbye.
Mottled Cattleya Leaves
Q. I was reading about fungal problems and noticed that many of my cattleyas have leaves that are becoming mottled. I have attached pictures for examples of what I am seeing. I am concerned that most of my cattleya plants are diseased.
A. Leaf mottling is typically caused by one of three things:
1 - Scale, turn the leaf over to make sure you don't have the dreaded boisduval scale on your cattleya.
2 - Fungal Infection, turn the leaf over and see if you see tiny dots or blotches of dots, the spores.
3 - Magnesium deficiency, which is what I suspect you have and what I had for many years.
Our water is very magnesium deficient and most fertilizers do not contain magnesium. Magnesium is an essential component of chlorophyll, that's what turns the leaves green. During extremes of heat and cold, the chlorophyll can degrade and give you that mottled appearance. I add magnesium sulfate, Epsom salts, to my fertilizer solution. Some people apply it in the spring and fall, others apply it monthly. I give mine Epsom salts every time I fertilize, which is every time I water. If you use 1/4 tsp/gal fertilizer, add 1/4 tsp/gal Epsom salts at the same time. The only caveat is you can't mix Epsom salts with a CalMag fertilizer, but with a CalMag fertilizer you shouldn't have to add supplemental magnesium.
Tiny Castings from Cork Mount
Q. I have a giant Dinema polybulbon mounted on cork. It was outside all summer, but now that it’s in the greenhouse, I realize that the cork is inhabited by something that is creating copious tiny castings. I’ve got a new piece of cork, and I guess I can re-mount the plant, but I’m worried that the critters will move into the new cork with the plant, and also move into my other mounts.
I found info about steaming and baking the cork, but I can’t do that with the plants on it!
A. That looks like frass from dry wood termites. You might try soaking the mount for an hour in a strong solution of imidacloprid, say double strength. That's not the strength they use to treat foundations, etc. for termites, but it's probably as strong as you'd want to try with your orchids. I don't think the termites will go after your plants, but of course you don't really want a colony of termites anywhere close to your house.