Orchid Culture Questions and Answers
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Questions and Answers from 2018
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!
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Orchid Needs Repotting
 

Orchid Needs Repotting

Q. This plant has not been repotted in years. It blooms all season, but never more than 5-6 at a time. I am content with it but was wondering if I should thin out roots.  

A. Never thin live roots. The central part of your plant has probably disappeared because the organic matter in the mix has turned to mush and rotted the roots. You may have to tackle a repot, get the roots wet and pliable, yank it out of the plastic pot and drop it into a large basket.   (Jun-18)


Bacterial Brown Spot on Cattleya
 

Bacterial Brown Spot on Cattleya

Q. What’s going on with this fella? It made it all the through the winter then bam!  

A. The discoloration on the oldest leaf looks like bacterial brown spot, so it is probably an air movement issue. Looking at the next two younger leaves, it looks like the tips were cut off, possibly because they too had the bacterial spotting. Consider cutting the oldest leaf off about an inch down beyond the yellow discoloration and think about repotting it. Bring it to the next Ace potting clinic and we'll help you with it.   (Jun-18)


Mites on Catasetum
 

Mites on Catasetum

Q. I have 60 catasetums growing in a screened room. I struggled to keep the mites under control last year so I am being aggressive this time around, but the first two catasetums that emerged from rest are already attacked. The other 12 that are already growing fast and being watered so no mite problems on them. I do not dare treat catasetums with emerging bulbs, so I have to wait until I start watering them. It frustrates me because it is indeed a lot of damage for a plant that just woke up. On top of that I sprayed Sultan on all of them when they went dormant because I am never sure if mites sleep in the root zone while the foliage is gone.  

A. How interesting. I just reread Johnson's article about mites, and he says the mites can live in the media. So perhaps what you really need is a drench instead of a spray. You can try the Bayer 3 in 1 if it has fluvinate in it. Kontos can be used as a drench, it is both xylem and phloem mobile, but it's pretty expensive and not recommended for use on orchids. Johnson recommends Avid, says it is the least toxic. Talstar or Bifen with the active ingredient bifenthrin is affordable and may be your best bet. It comes in a granular form (I use it for fire ants but the active ingredient is effective on mites), and as a liquid.   (Jun-18)


Is This Black Rot
Is This Black Rot
 

Is This Black Rot?

Q. Ugh, another one today. The stem gets very dark and bends. This one feels dry and dead at the bend but others have been mushy. I’d like to save it. If you have no other ideas I will unpot, treat with Ban-rot and mount.  

A. What you have is black and it is rot, but it is not the dreaded black rot caused by the water molds Pythias and Photography. You have a situation where the papery sheath around the pseudobulb was pocketing water and the water sitting in this pocket was invaded by the bacteria omnipresent in the environment that attacked the tissue and rotted it. When you have that tissue pocketing, it is a recipe for disaster, so you have to watch and peel it down so it cannot hold water. Then, the problem never arises. Alternatively, you could pour hydrogen peroxide in all these little water pockets, but it's a lot easier to just peel that tissue down so water cannot pocket.   (May-18)


Water Soaked Leaves
 

Water Soaked Leaves

Q. My friend sent me a picture of a phal that looks water logged. It currently has buds on it, but she said the leaves were soggy.  

A. Your friend's phal is probably history. It looks like it has the fast moving bacterial soft rot caused by Erwinia and it looks like it has infected the entire plant. Even with the blooms, she should discard it to make sure the bacteria doesn't spread to other plants.   (May-18)


Yellow Cattleya Leaf
Yellow Cattleya Leaf
 

Yellow Cattleya Leaf

Q. I bought this L. tenebrosa a couple weeks ago. The seller told me the yellow leaf on the old pseudobulb was just from being exposed to more light and it would “green up“ if I put it in less light. It has not. Mostly I would just like to rule out a disease. The newer pseudobulbs look pretty good.  

A. I hope you misunderstood the vendor. If the issue was too much light, all the leaves would have had that yellowish cast and of course it is only the oldest growth that has the yellowing leaf. I suspect your plant was not fed enough magnesium and is robbing the older leaf of magnesium to supply the new growth. The yellow leaf will ultimately die and drop off. Our water tends to be very magnesium deficient, so add Epsom salts when you fertilize at the same rate that you are applying the fertilizer.   (May-18)


Cold Damage on Dendrobium Leaf
 

Sunken Spots on Dendrobium Leaf

Q. I'm a long time member ofthe Memphis Orchid Society, and I noticed this problem when the orchid was returned to me from our society exhibit at the St. Louis orchid show just a couple weeks ago. I already removed the two top leaves from the pseudobulb, that looked exactly like the ones in the attached pictures of my Den. Sherry Abe that was awarded an AM/AOS last year.

A. My first thought is cold damage. I looked up your dendrobium in OrchidWiz, which indicates its parentage includes the phalaenthe and latouria sections, so it is likely very cold sensitive. Is it possible it was chilled in the trip to and from the show? Was the plant out of your care for more than a weekend? Those types of dendrobiums drop leaves easily if too cold, too dry, etc. from what it is accustomed to. The good news is the plant is going to be fine, this is just a temporary setback and it will throw off new growths in the coming months.   (Apr-18)


Black Spot on Phal Stem
 

Black Spot on Phal Stem

Q. Is this black mark on my phal a disease? It seems to be expanding. How should I treat it and will the spike be affected?  

A. That phal looks very happy and healthy. The black mark is probably from water pocketing at the leaf base. Pour or spray some fresh hydrogen peroxide on that area of the phal and just keep an eye on it. It is probably bacterial in nature but it doesn't look like a big problem. Peroxide should take care of it and your spikes should continue to grow just fine.   (Apr-18)


Spot on Cattleya Leaf
 

Spot on Cattleya Leaf

Q. What is causing this spotting on my cattleya?  

A. That looks like the leaf spotting fungus Cercospora that forms irregular purplish brown blotches on the leaves. A good general purpose fungicide for the leaf spotting fungi is Cleary's 3336 which contains the active ingredient thiophanate methyl. It is sold in smaller, more available quantities as Thiomyl or in combination with another chemical as Banrot. Daconil, that you can get in the local nursery, is also rated very good to excellent for Cercospora. To be cautious, you can remove the leaves with the pentagonal blotching and then spray. I've actually left the leaves on and really didn't notice it spreading, but if you remove the infected tissue, you will remove the spores that spread the fungus.   (Apr-18)


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)


Orchids Left Out in the Cold
Orchids Left Out in the Cold
 

Orchids Left Out in the Cold

Q. I left these outside during the cold wet weather. Yikes! They're inside now, what do I do?  

A. The phalaenopsis may be a goner. Whether the damage is from the freezing temperatures or dripping cold water, the cells have collapsed and been invaded by bacteria. You can remove the leaves, spray the entire plant with hydrogen peroxide or one of the copper fungicides/bactericides. Put it in a warm place and then you wait, perhaps a basal keiki will form.
    The other orchid, a Grammatophyllum perhaps, also has some extreme cold damage. Remove those leaves that are totally or mostly brown. If you choose to keep some of the greenish leaves, spray them with peroxide and watch the leaves. If the discolored areas continue to enlarge, remove them. There is a lot of energy stored in those pseudobulbs, so your hope is that they will sprout new healthy growths in the spring.  (Feb-18)


Dendrobium Leaves Yellowed
Dendrobium Leaves Yellowed
 

Dendrobium Leaves Yellowed

Q. I have has this phal type dendrobium for several years. The plant is in a southeast window with some phals (house temp about 65 F, about 60 miles north of NYC). It hasn't produced many spikes over the years but it has 6 canes that had, until a couple of days ago, green leaves and was looking pretty happy. Is the leaf yellowing a bad thing?   

A. The phalaenthe dendrobiums are very cold sensitive. I am guessing it was too close to the window on a cold night. The good news is that dendrobiums are tough. As long as the canes are hard, they'll probably come back. Feel the canes from the base to the top looking for any soft or dessicated spots. It looks like the canes are a little deep in the pot, why don't you try picking some of the bark out of the top of the pot until you can see the rhizome, then feel the cane at the very base to make sure there is no rot. If nice and hard, find the brightest spot you can in the house and just wait and watch, cut back on watering to say half your normal rate until you see some new growth.   (Feb-18)


Psychopsis Leaf Yellowing from Base
 

Psychopsis Leaf Yellowing from Base

Q. Just noticed the base of leaves of this Psychopsis are turning yellow. Do you think the two nights below 60 caused this?

A. I don't think it's the cold weather; those Psychopsis oncidiums can be very temperamental. I think it is a form of rot that comes up from the roots through the pseudobulb to the leaves, possibly rhizoctonia cause it isn't fast like black rot. When that yellowing occurs, that part of the plant is probably toast. Move the organic matter away from the pseudobulbs and from above the rhizome. See if there are any roots attached to the oldest pseudobulbs and whether the bulbs are hard or soft. If the roots are gone, the bulbs softening, cut them away and then decide whether you should repot, which could hasten the end, or let the plant try to recover, in which case give it a Banrot drench.
  I've lost beautiful psychopsis that went from having 6 consecutive flower spikes blooming like mad to exhibiting this slow moving rot where one leaf after another drops. I've had some suggest it's salt accumulation, though I've rarely found a high salt content in the coarse mix. I keep mine in a somewhat shadier spot than the cattleyas in a mostly inorganic mix. Just leave them alone, let them grow out of the pot and don't disturb the roots, sometimes a leaf yellows and drops and as long as the bulb is hard, just let it do its thing.   (Feb-18)


Enlarging Rings on Orchid Leaves


 

Enlarging Rings on Orchid Leaves

Q. I have these rings on a Gongora, as well as two other orchids. It starts with one leaf, I cut it off and later on, other leaves develop the same problem. I thought it might be the sun at first but I remember reading that circular patterns are a sign of virus. Should I trash these 3 orchids fast?

A. I don't think that's a virus, it looks like classic Anthracnose, that is caused by one of the leaf spotting fungi. You should be able to see tiny little dots in the discolored area, those are the spores that spread the disease. You can remove the diseased leaves to a closed container. Fungicides can be sprayed to help prevent spores from settling on leaves and spreading the infection. More air movement and less leaf wetness will help prevent the conditions that favor the disease.   (Jan-18)


White Crystalline Material on Potting Media
 

White Crystalline Material on Potting Media

Q. What is this white stuff all over my lava rock? I am repotting cause so many roots were growing out of the pot on my oncidium.

A. Quite a mystery! It's not snow mold. That grows on organic media, and this substance is crystalline. You might think salts precipitated out of the water, but then why are the roots so healthy,with none of them burned? Courtney says there are some bacteria that make colonies and use dissolved minerals as an energy source. The white material, possibly calcium carbonate, dissolved when dropped overnight in a solution similar to vinegar. It doesn't seem to impact the health of the plant. Just another of life's little mysteries!   (Jan-18)


Oozing Spot on Phalaenopsis
Oozing Spot on Phalaenopsis
Oozing Spot on Phalaenopsis
 

Oozing Spot on Phalaenopsis

Q. Someone just gave me this orchid and I can’t identify its problem. Can you help identify it and give me some treatment options?

A. The bottom leaf has soft rot, that leaf should be removed immediately. If the rot travels to the crown it will kill the plant. The upper and lower surfaces of the other leaf looks comprised as well. If the plant has enough other leaves to sustain it, you might consider removing that leaf too. Then get a fresh bottle of hydrogen peroxide, or better yet one of those spray bottles of peroxide that Walgreen's sells, and spray all the above ground portions of the plant, particularly around the crown where the rotting leaf was. If you were just given the orchid, then you don't really know what happened to it before that allowed the rot to get to the plant. You'll just have to keep an eye on it to see if you stopped the rot in time. If you're a cinnamon person, you could dust the crown of the plant and around the cut edges after the peroxide dries. The cinnamon will dessicate that portion of the plant and create a barrier so bacteria can't invade.   (Jan-18)


Phal Leaf Didn't Open
Phal Leaf Didn't Open
 

Phal Leaf Didn't Open

Q. I rescued this tiny Phalaenopsis about four months ago. It was dehydrated due to total root loss other than 4 small aerial roots. It has shown some improvement, the leaves are no longer limp, and it has managed to grow two more aerial roots. I am not sure if there any new roots growing in the media yet. It also started to grow a new leaf about 2 months ago but it has shown no signs of opening up by now. Why?  

A. Your plant is going to be fine. I like your mix, the addition of sphagnum moss to the bark, that will help hold a little moisture cause bark oftentimes is hard to get hydrated when you first put it in the pot. The mix looks perhaps a bit dry, are you growing indoors where the humidity is low? Are you watering once or twice a week? One thing you can do is put a thin layer of sphagnum on top of the pot to help hold a little moisture at the upper end of the pot where the tender new roots will form. If you just repotted and the leaves are starting to lose their leathery look, I'd say your plant is well on its way to recovery. Make sure it's getting enough water and it'll come out of its holding pattern and the leaves will start enlarging. A few weeks later Alicia wrote back, "Good news! The leaf is now open!"   (Jan-18)


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