Orchid Culture - 2019 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 Marring on Flower

Black Marring on Flower

Q. I sent pictures of this orchid to the vendor, who told me it was thrips. I have many blooming orchids in my greenhouse and no other flowers have been affected. If it was thrips wouldn't other flowers be affected?
A. Thrips are evil, it probably had thrips hidden in the buds when you brought the plant home. You can spray buds and flowers with Orthene once or twice a week if you notice floral damage from thrips, or drench the pots every 6 weeks or so with an Orthene solution.   (Jul-19)
 
 
Brown/Black Splotches on Leaf

Repotting Bifoliate Cattleya

Q. Is it too late to repot this Cattleya?
A. People live in fear of repotting amethystoglossa! The roots are long enough that they will branch if broken, so you can repot. But think of doing it Keith Davis style where you situate the plant in its new home on styrofoam, lava rock or some other airy substrate and then just put in a handful of media, so you can watch for the roots to branch and when they do, you add a handful of media every week into the pot so the new roots will grow into the new mix.   (Jul-19)
 
 
New Cattleya Lead Rotting
New Cattleya Lead Rotting

New Cattleya Lead Rotting

Q. My Lc. Blue Boy (C. Ariel x Lc. Elegans) had what appeared to be a healthy new growth. Several days ago I noticed a drop of ink black liquid on the tip. The following day there was some more. Yesterday the growth was black and mushy. The leaves all appear to be healthy. I repotted it and cut off the affected parts. There is still another new growth which I hope will develop normally. What am I dealing with? I corrected my potting issue with a shallower pot, mixing in aliflor and charcoal along with large orchiata. I grow all my orchids outside under palms and large oaks and the rest of them are thriving!
A. I'm guessing you had some water in the crevices of the new growth and it got a bacterial rot. I remember Keith Davis' tip on growing bowringiana, where he said he takes a plastic pill cup and puts over the new growth til it gets a bit larger to prevent rots. I don't think it had anything to do with the potting mix or roots. A peroxide spray might help too, after rain with new growths starting.   (Jul-19)
 
 
Leaves on Cattleya Yellowing

Leaves on Cattleya Yellowing

Q. I’m having yellowing of Cattleya leaves. Mostly it is on older leaves. However, quite often the yellowing extends a lot closer to the front than I would expect from simple senescence. Sometimes it involves the second or third bulb back from the front, sparing the back of the plant - but this is not typical. Last year I took samples to the agricultural extension here in Nashville and was told it was nutritional, not insect or disease. It starts in the leaves and not in the bulbs. Generally it doesn’t kill the plant and I have even seen leads break from eyes in the affected tissue. It occurs in a patchy fashion throughout the greenhouse.
A. I used to see lots of leaf yellowing in the early spring when growth begins before I started using magnesium supplements with every watering. Now I use a calcium and magnesium supplements to maintain a Calcium:Magnesium ratio of about 2:1. The standard Cal Mag fertilizers don't seem to have enough magnesium for my water quality. Since I started using tons of Epsom salts, the leaf yellowing is significantly less, but I still get some, which I'm hoping is just senescence.   (Jun-19)
 
 
Brown/Black Splotches on Leaf

Brown/Black Splotches on Leaf

Q. I am a newbie to orchids but purchased an a cattleya about 2 months ago on Ebay. It looks overall healthy but has developed brown/blackish splotches (not raised) on the underside of the leaf and has a mottled yellow color to the top of the leaf. It looks most like brown spot (pseudomonas) or black rot (yikes!).
A. That looks very much like Cymbidium Mosaic Virus on the leaves. If it is virus, it probably came to you that way. If the black leaf markings were present when you got the plant, you should contact the vendor about a refund. If you want to be sure before tossing the plant, you can test it for virus. If you don't have a virus test kit, you can send a sample off to Critter Creek and they'll analyze for $5. Cut off a 2 inch or so section of leaf from the edge of the affected leaf and send it off to them for testing, that way you'll know for sure.   (Jun-19)
 
 
New Orchids Develop Disease

New Orchid Develop Disease

Q. This phal species that I purchased at a recent orchid show died. My orchids are fine but I’m terrified of what I’ve introduced to my orchids. Is this bacterial or fungal?
A. That is terrible news! The phal developed bacterial soft rot, caused by Erwinia (except now they call it Pectobacterium). As you have discovered, it is very fast moving and can destroy a plant within a day or two if it reaches the crown, which it sounds like it did. It takes awhile for plants to acclimate to your growing conditions. They were probably growing in a greenhouse environment and getting sprayed regularly to prevent bacterial and fungal infections, and then they were placed in a truck and on sales benches for a couple days til they moved home with you. Perhaps you should consider a good spray with drugstore hydrogen peroxide over all the plants you brought home, undiluted, top to bottom but not on the roots. Keep them isolated to see if any problems develop over the next month or so.   (Jun-19)
 
 
Leaf on Catasetum (?) Yellowing

Leaf on Catasetum (?) Yellowing

Q. Is this a Catasetum? I’m concerned about this second yellow leaf.
A. I think that is a Grammatophyllum, a close relative to catasetums, but these don't lose their leaves in winter. They tend to be mite magnets and your plant shows evidence of mite damage. You can spray a miticide like Avid (normal insecticides won't kill mites, which are in the arachnid family) or you can water blast the leaves with a nozzle set on flat and then spray the entire plant with alcohol or alcohol with dish soap, perhaps repeat weekly for a month or so.   (May-19)
 
 
Is This a Bud?
Is This a Bud?

Are These Buds?

Q. Could these possibly be buds?
A. It sure looks like it. They're called the bud primordia, the tissue from which the flowers will ultimately form. (May-19)
 
 
Spots on Vanda Flower

Spots on Vanda Flower

Q. I recently purchased some more orchids (a recurrent problem) and one was a blooming vanda that had questionable spots on the flowers. If it is Botrytis, what is the best course of action? Being in west Texas, the humidity is super low, but I have been running a humidifier so it’s felt much more jungle like in my sunroom lately.
A. I don't think it is Botrytis, a fungal infection causing small dark spots on the flowers. You may have two things going on, the black sunken spots may be some sort of bacterial infection and the raised, corky spots are probably edema. Edema is like a blister when the plant absorbs more water than can be shed through transpiration, happening more on leaves than flowers. It happens when you water late in the day and the nights turn cool or when you water on a gray rainy day. It doesn't really harm the plant. Look at the spots, if they are sunken, think bacterial infection, but if raised it is more likely edema. (May-19)
 
 
Black Pitted Spots on Cattleya

Black Pitted Spots on Cattleya

Q. That looks like bacterial brown spot, a slow moving bacterial disease in mature cattleyas. I wouldn't cut anything off. When it's done blooming and you get ready to repot it, you can cut off all the old ugly stuff and pot up the front half. It'll look brand new!
A. I used to see lots of leaf yellowing in the early spring when growth begins before I started using magnesium supplements with every watering. Now I use a calcium and magnesium supplements to maintain a Calcium:Magnesium ratio of about 2:1. The standard Cal Mag fertilizers don't seem to have enough magnesium for my water quality. Since I started using tons of Epsom salts, the leaf yellowing is significantly less, but I still get some, which I'm hoping is just senescence.   (Apr-19)
 
 
Spots Spreading on Phalaenopsis
Spots Spreading on Phalaenopsis
Spots Spreading on Phalaenopsis

Spots Spreading on Phalaenopsis

Q. I am a newbie to orchids but purchased an a cattleya about 2 months ago on Ebay. It looks overall healthy but has developed brown/blackish splotches (not raised) on the underside of the leaf and has a mottled yellow color to the top of the leaf. It looks most like brown spot (pseudomonas) or black rot (yikes!).
A. It looks like it started with sunburn, that's the circular dark spot. Then maybe a secondary infection kicked in and spread into the leaf. Also looks like it hasn't been repotted in a while so I would wonder about the condition of the roots. I would cut off the extremely damaged leaves about an inch below the discoloration with a single edged razor blade. Then I think let it keep blooming and enjoy it. Somewhere in the June time frame, it'll be time to cut off the blooms, repot the plant, allow it to recover from the transplant shock, grow new roots and then bloom for you next year. Your local orchid society can help you.   (Apr-19)
 
 
Cymbidium Repotting

Cymbidium Repotting

Q. This cymbidium is over 10 years old, repotted once, and now huge! It’s growing more spikes and bigger flowers this year than ever before. It grows outdoors by the pool inside screen enclosure full sun. I’m wondering if I can just find a bigger pot and repot without breaking it up?
A. What a show your cymbidium is putting on! Harry, the Cymbidium expert, had this to say: If most of the bulbs have leaves, consider potting up to a bigger pot. Best not to over pot so get a pot with one to two inches of growing room all around the pot. Pull the plant out of the pot and inspect the roots. If the roots look healthy just wash out as much of the old media as you can if it is an organic media. If it's hydroton or some other inorganic media, just pot up without washing out the old media.
  If there are a lot of leafless backbulbs, you should divide it before repotting. If you find a lot of dead roots you will need to dry the plant so you can separate the roots easily (maybe easier is the word), cut off 1/2 of the root ball. It sounds drastic but the rot will continue and is not good. Cymbidiums grow new roots quickly. It may destroy the plant if the rotten roots are not cut off. Remove as many of the rotten roots in the remaining root mass as is practical. Spray the cut area with a fungicide (Daconil or Thiomyl) and repot.   (Apr-19)
 
 
What to Do with Aerial Roots

What to Do with Aerial Roots

Q. My oncidium is firmly established in the pot but the roots are exposed and hanging over the edge. Should this be repotted in the early spring and should the roots be covered with the medium?
A. Roots adapt to what they are growing in, aerial roots that have adapted to growing in the air will not adapt well to growing in media, roots adapted to growing in ProMix will not adapt well to growing in bark, etc. So, when time comes to repot in the spring, I would give the aerial roots a hair cut, so they would fill perhaps 2/3 of the pot. Get the plant situated in the pot, and put an inch or two of medium in the pot, and then as you see new rootlets branching from the aerial roots, you can backfill a little each week so the new rootlets will grow into the new mix and adapt to that mix.   (Mar-19)
 
 
Soft Brown Rot on Cattleya

Soft Brown Rot on Cattleya

Q. This cattleya has soft brown discoloration, what should I do?
A. That looks like Rhizoctonia, that is moving from the older part of the plant through the rhizome to the forward part of the plant as well as moving up the pseudobulbs. You will have to cut away all the infected tissue and repot the healthy growing leads into fresh mix.   (Mar-19)
 
 
Phal has Sunken Markings
Phal has Sunken Markings

Phal has Sunken Markings

Q. This phal species that I purchased at a recent orchid show died. My orchids are fine but I’m terrified of what I’ve introduced to my orchids. Is this bacterial or fungal?
A. I suspect mites, from the stippling pattern, and the warm dry location in the house. Sometimes you have to get a magnifying glass to see them, or wipe a kleenex across the bottom of the leaf and see if you find little dark blotches on the kleenex. I would suggest you take it to the sink and give the leaves a thorough bath top and bottom with the sink sprayer and then get a spray bottle of isopropyl alcohol and spray the leaf surfaces, perhaps making the alcohol spray a weekly ritual. Belinda updated us "I just wiped it with a tissue and the tissue was a rusty color with tiny dark specks."   (Mar-19)
 
 
Repot Cattleyas When New Roots are First Forming

Repot Cattleyas When New Roots are First Forming

Q. When we are told to repot cattleyas when you see new roots, does that mean green tips and a bit of growth? The green tips are getting a bit brighter and larger but no outward growth yet.
A. The ideal time to repot cattleyas is right before they form roots, when you see the little nubs beginning to form. That way you can repot without worrying about damaging the tender new roots so they will grow quickly into the new mix. This one could have been repotted a week or two ago, repot immediately!   (Feb-19)
 
 
Phal Leaf Markings

Phal Leaf Markings

Q. What is wrong with this phal? It’s next to a window with other phals, but it’s the only one with a problem.? There have been no major changes in light or watering.
A. On first glance, it looks like edema, a blistering of the leaf that occurs when the leaf can't transpire moisture fast enough, such as when you water late in the day and the night turns cool. This looks like the damage occurred a while ago.   (Feb-19)
 
 
Phal Lost Its Blooms

Phal Lost Its Blooms

Q. We received this orchid a week ago as a gift. It had beautiful dark pink flowers. I promptly put it on my kitchen windowsill, and I’m afraid it might have gotten too cold there?
A. Those flowers have blasted. Bud blast happens for a whole host of reasons, it could be from being moved, from being too dry, or too cold. If it happened very suddenly, as in overnight, it is very likely it was too close to the window on a cold night. The good news is the plant looks fine, and though it won't bloom again this year, you should be able to bring it into bloom next year.   (Feb-19)
 
 
Angraecum Leaves Come Off at Base

Angraecum Leaves Come Off at Base

Q. Some of my angraecums lose many leaves that come off at the base. The leaves that fall are seemingly healthy, why?
A.I suspect water is accumulating at the base of the leaf and causing the rot. The thick angraecum leaves are so close together that unless there is really buoyant air movement, you can get this sort of rot at the base of the leaf.   (Jan-19)
 
 
White Filamentous Growth on Bark
White Filamentous Growth on Bark
White Filamentous Growth on Bark

White Filamentous Growth on Bark

Q. I've got snow mold growing in my pots. The mix is 60% Orchiata and 40% clay pebbles, less than 2 years old. What causes it and what can I do to get rid of it.
A. Our go-to-guy Courtney handled this one. That does not look like the Snow Mold I “know and love” (shown in the bottom image). Snow Mold becomes hydrophobic when it forms its mats and almost peels like skin. Usually the bark it is on also feels dry even after you water. In the old days redwood chips were added to keep the pH acidic in bark mixes. Snow mold was especially a problem with fir bark as it was not very acidic even when it was decomposing. Orchiata is supposed to become very acidic as it ages.
  The white stuff looks like hyphae, indicating filamentous fungi, hence the mushroom. My guess from the photos is that the fungi is feeding on the Orchiata. I am surprised that you are getting it using rain water as the Orchiata should be acidic enough to keep fungi off.
  I like a mystery. Let’s figure out what this is. Fungi are devils to identify unless there are fruiting bodies. Send your photos (mushrooms) to the U of Fl agronomy department. They may have or know a Mycologist that can get an ID for you.
  Follow-Up Comments: The filamentous fungi is feeding on the bark, so it will ultimately decompose the mix although the grower says the mix was not decomposing after 2 years in the pot. This kind of fungus does not cover and smother the roots the way snow mold does. Snow mold poses an immediate threat to the orchid's health and this filamentous fungus does not appear to pose this same danger. The sure fire way to get rid of the fungus is to repot the orchid.   (Jan-19)
 
 
Brown Spotty Patches
Brown Spotty Patches
Brown Spotty Patches

Brown Spotty Patches

Q. Yesterday I picked up a few plants and now am worried that they may have problems. This Dendrobium kingianum has new growths that are blemish free, but the older leaves have these brown spotty patches. Do the cattleyas have sunburn?
A. That kingianum seems to have one of the leaf spotting cercosporoid fungi. Remove the severely affected leaves so they won't infect the new leaves. Then you can spray with a fungicide for leaf spotting fungi. The Fungo-o-nil that you bought contains the active ingredient chlorothalonil, same as Daconil, and it is effective on leaf spotting fungi. But remember, most fungicides don't cure an infection, they prevent a plant from becoming infected, so it won't fix the problem with the older leaves. Remove and discard the leaves and then spray. These fungi also affect cattleyas, the dotting on the leaf undersides is the cercosporoid spores, but they don't seem to have as severe an impact on cattleyas as on some other genera. Spray them monthly, and when you repot, remove as much of the infected tissue as you can.   (Jan-19)