Orchid Culture - 2010 Questions & Answers
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Fungal Leaf Spots on Dendrobiums
Q. I have a number of older orchids growing on trees down in South Florida. They are currently covered with light and brown spots. I have attached a photo of each side of one of the leaves, showing the problems, as well as one of the area affected
(in better times) How can I return them to health?
A. Those are some beautiful dendrobiums in bloom! It looks like you have fungal leaf spot caused either by Cercospora
or Phyllosticta. It doesn't much matter which because the cure is the same. Spray with a fungicide containing the active ingredient
Thiophanate Methyl, like Cleary's 3336 or Banrot (available from OFE International
). Apply it as a spray to the leaves (2 tsp/gal) or a drench
to the media (1 tsp/gal). Different fungicides and their application rates
for Leaf Spots are provided in the spreadsheet at the top of the orchid
diseases webpage. If it weren't a dendrobium orchid, you could use a copper fungicide, which is very effective and cheaper than Cleary's 3336 or Banrot, but dendrobiums have an adverse reaction to the copper. Copper fungicides will also mar the flowers.
- The bad news is that the leaf spotting will remain on the leaf after the
fungus is no longer active. Ultimately the dendrobiums will lose the
infected leaves. The good news is that dendrobiums are very spunky and
resilient orchids and will grow new canes with new leaves to sustain
themselves. The best news is that dendrobiums will bloom from old and
- The thing we have to ask is why did the dendrobiums suffer from a fungal
infection? The obvious answer would be too much leaf wetness or too little
air movement. You've got your dendrobiums in a perfect place in the trees
and they obviously get plenty of air movement normally, so that's not the
problem. We up in north Florida had a very very dry fall, though I
understand south Florida had lots of rain. Perhaps you got fungal
leaf spotting from leaf wetness this autumn. When you have wet gray
weather for extended periods during the fall (or any season for that
matter), perhaps you should consider preventative spraying, perhaps monthly,
to prevent the fungus from taking hold, following all label instructions. Next year your dendrobiums will be beautiful once again!
Encyclia Culture (Enc. oncidioides x Enc. cordigera)
Q. A couple years ago, I bought an encyclia at EFG. Last year it sent out a spike which I promptly broke when
moving plants in. I believe the label is Enc. oncidioides x Enc. cordigera. It may be a February bloomer, brown with a fuchsia lip. I just took it out of its plastic pot and placed it in a larger basket without disturbing anything. Can you verify the name and tell me anything about it.
A. The Enc. oncidioides blooms May to July, mostly in
June and the Enc. cordigera blooms February to July, mostly in May, so your primary hybrid should bloom in the May to June time frame. Your cross is
unregistered, so your label is correct (Enc. oncidioides x Enc. cordigera).
There are different color forms for each so you'll have to bloom it to be
sure, but bronze with a fuchsia lip sounds likely and it should also be
fragrant from the cordigera. You'll let it rest a bit in the winter
reducing water and fertilizer like you do for your other cattleyas and
taking it out of plastic and putting it into a basket should be good for it.
Encyclias like a coarse freely draining mix that dries rapidly after watering and
should be repotted immediately if the mix starts to break down.
Water Plants Before Fertilizing?
Q. Some of our speakers recommend that we water our orchids before fertilizing them and other speakers say not to water before fertilizing because the wet root is saturated and can't absorb the fertilizer. Which approach is correct?
A. Both, depending on the orchid specifics. First, let's think about the orchid roots. Orchid roots are a wiry filament cortex surrounded by a sponge-like velamen that actually stores water. During periods of dryness, the surface of the root is hard and stiff to help prevent water loss. After wetting, the root become soft and pliable and acts like a permeable sponge soaking up water and fertilizer. If the root is saturated with water dripping off it, of course it can't absorb any more fluid. But the idea behind prewatering is to get the velamen to be open to absorbing the fertilizer after the root begins to dry.
Now to the specifics:
- If you have an orchid in a water retentive mix like sphagnum moss, you don't need to prewater before fertilizing because the mix itself will stay wet for about a week and the roots will absorb the water and fertilizer from the sphagnum.
- The opposite extreme would be an orchid mounted or in a basket without any mix such as a vanda. It is almost impossible to overwater a vanda where you saturate the roots to the point of dripping and they are mostly dry an hour later, so you can repeat this multiple times a day. Clearly you could fertilize the vanda in lieu of one of the waterings.
- Somewhere in between is an orchid planted in a freely draining mix. During periods of low humidity, when plants require an abundance of water, try watering at night so the roots will remain moist all night and you can fertilize early the next morning when the roots are still receptive to fertilizer. Perhaps in the winter, you would water and fertilize in a single step in the morning or an hour apart.
Fusarium on Vandas
Q. I live in the coastal northern plain in Puerto Rico. My vandas
are in baskets hanging under trees. Their roots are exposed to the
elements always. All the root tips are dying. They look shriveled and
brown like something sucked their juice out. They are losing the lower
leaves and a black dust, like coffee grinds, is collecting in the axils. The
stem is turning black and is covered by a black dust very similar to sooty
mold. I cut the stem of one of the worst ones and found purple markings
inside. Could it be fusarium? Please answer, my beloved vandas are dying
A. Fusarium. Vandas do get fusarium and the purple ring you found confirms
your fear. You can start cutting away the infected stem in short sections
(sterilizing your cutting tool after each cut) from the bottom up until the
purple ring is gone and then soak the plant in a good fungicide like Banrot, Subdue or Cleary's 3336. According to David Grove's book Vandas and Ascocendas, to prevent conditions favorable to
fusarium, use only fertilizer with the nitrate form of nitrogen rather than
blends containing urea or ammonia nitrogen. You can also make up a lime
solution (1 tbsp per gallon) and after you soak the roots, spray with
the lime solution (shaking the sprayer to keep the lime dissolved) every two
weeks or so.
- Root Damage. If the roots look like they are girdled, you may have thrips.
You can spray with Orthene, Conserve or the systemic Bayer product containing imidacloprid. If it's not thrips, it may be a cultural issue, perhaps too much fertilizer
(fertilizer burn) or too dry.
- Losing Leaves. As vandas age, they will lose the bottom leaves and
ultimately you'll get keikis at the base and can top the plant. However, it
sounds like yours are dropping due to some problem. Normally you would
think it is caused by a cultural problem (too dry or too cold) or plant illness. The leaf drop may be related to the fusarium infection.
- Sooty Mold. If it looks like sooty mold, it probably is sooty mold. Get
some physan or 10% pool algaecide and spray the plants (2 tsp/gal).
- Nursing Stressed Plants. Grove has some good advice for handling stressed plants. He recommends
several weeks of hanging the plant upside down in a shady humid location
having air movement. This will prevent fungus and bacteria from lingering
in the leaf axils and reverses what he calls apical dominance. Hanging the
plant upside down reverses the internal flow of hormones that normally
inhibit root and lateral shoot growth to direct more energy to the top of
the plant. As a consequence of hanging upside down, the energy is diverted
from the production of new growth at the old top of the plant to producing
new roots in what is now the uppermost section. To do this, bareroot the
plant, wash the roots (try a spray nozzle set to flat) and cut off any dead
roots, remove the fusariumed section of stem, soak in the fungicide solution for
say an hour and then suspend it upside down in a shady spot. Once new roots
have emerged from the stem and are an inch long, you can rebasket it and
gradually increase the light to which it is exposed until you can return it
to its normal location.
Cattleya Leaves Dehydrated
Q. The leaves on one of my cattleyas are turned in. They look like a rhododendron leaf that is responding to cold weather. What do you suppose is wrong?
A. The plant looks dehydrated. When I'm not sure what is going on with a plant, I knock it out of the pot and take a look at the roots to see if they are healthy and growing vigorously. If the roots look desiccated, try watering or increase the organic matter in your potting mix.
Sunburn from Changing Sun Angle
Q. Is this a bacterial or fungal infection?
A. Neither, the sun angle is changing as we move into fall and I think this vanda leaf got sunburned (see how the burn is concentrated on the highest point of the leaves where the sunlight is most intense). I've gotten sunburn in the last few weeks on plants that have been in the same position all summer long.
Bacterial Brown Spot on Vanda
Q. My vanda has black spots surrounded by yellow, making me think the vanda has a bacterial infection. I have sprayed it with captan a few times this year. What do you think?
A. The yellow halos together with the sunken necrotic spots both point to Bacterial Brown Spot caused by Acidovorax (Pseudomonas). Spray with a bactericide containing copper compounds (best, but don't use on dendrobiums) or you can use the somewhat less effective Consan, Physan or pool algaecide.
Thrips Cause Bud Blast
Q. I came across your website while searching the internet. I was wondering if you could help me identify the problem. What causes the buds on my vandas to dry up?
A. Bud Blast can be caused by many environmental factors (too dry, too wet, plant recently moved, etc.). The most likely culprits on vandas are either the plant is too dry or you've got thrips. Given how healthy your vandas look with plump leaves and plump roots, the bud blast is most likely caused by thrips. Thrips are tiny flying insects that attack the tenderest parts of the plant, the emerging buds, flowers and roots. To check for thrips in flowers, hold a piece of white paper under the flower and shake it. If little long moving black spots appear on the paper, you have thrips. You can also check your roots for evidence of girdling.
Thrips are difficult to control because they are mobile and you hate to spray pesticides directly on the flower where the thrips are. Keep a hand sprayer filled with an Orthene solution handy and spray flowers and buds weekly. You may also have to spray your landscaping to control the source of thrips, particularly if there are citrus, gardenias, eucalyptus, lots of flowers, etc. The Bayer product containing imidacloprid is systemic and can provide extended control but it will cause floral damage if you spray the flowers.
How and When to Top a Vanda
Q. I was given this vanda in June. The roots have put on numerous side roots as well as 6 new thick roots that are 3 to 8 inches long. Is it too late to cut this one up to see if the top will continue to grow and if the bottom will form a keiki?
A. It is a little late to rebasket a vanda though there are still 2 months or so in the growing season. However, if you top the plant below the new roots and basket the plant, the top plant will not be a pretty plant because the bottom half of the stem will still be bare of leaves. Perhaps it would be better to let the plant continue growing until keikis form at the base of the plant. Once the keikis mature, you can cut the stem above the keikis and have an attractive plant in the original basket.
Then you'll have to make a decision on what portion of the top plant to keep and rebasket or tie to a wire hook.
Catasetum Growing Keikis on Pseudobulb
Q. I purchased a Catasetum last fall after it had bloomed but it still had leaves on its 2 newest pseudobulbs. Later in the fall it went dormant and lost all the leaves. After leaving it very dry until new growth started in February, it was repotted in fresh sphagnum. The new growth was from the base of one pseudobulb. Now new growths have started from the base of the other pseudobulb, but the bulb is getting soft, like it is rotting. Should I cut the soft part off close to the new growth or just leave it alone and hope it does not affect the new growths?
A. Some orchids, including phalaenopsis, vandas, dendrobiums and catasetums, can produce adventitious growths on vegetative parts of the plant. In your catasetum, the keiki growing from the base of the rotting pseudobulb is the catasetum's survival mechanism. The keikis form from the adventitious tissue along the circular nodular bands of the pseudobulb. You can let the keiki grow attached to the pseudobulb or you can lay the pseudobulb horizontally on the surface of a pot packed with sphagnum and let it root into the moss. For this plant, cut away the rotted pseudobulb above the keiki and drench the plant with a fungicide like Banrot or Subdue.
Black Rot Traveling Up Cattleya Pseudobulb
Q. Two years ago I bought a nice orchid with orange flowers, Pot. Orange Bird. Its parentage goes back to hybrids developed by some of the great growers in the early 1900's. It has new growth in 3 directions this year but there is a dark area on the central rhizome which goes up about 1 inch on an adjacent pseudobulb. The base of the affected pseudobulb is a little soft. What do you recommend?
A. That is Black Rot along the rhizome and traveling up the pseudobulb. Black rot is a very fast moving disease that infects cattleyas during the hot humid summer and can kill the entire plant unless you perform radical surgery. Cut out the obviously infected tissue and treat with a heavy duty fungicide like Banrot or Subdue. You'll need a chemical that is listed as controlling Pythium and Phytophthora that cause Black Rot.
Vanda Leaves Dehydrated
Q. My vanda types are showing new leaves but the older leaves are "wrinkly". They are in full sun til about 11am and 50% after that. I thought they looked dehydrated so I started the summer nighttime watering regimen Courtney Hackney recommended in last month’s Tips. The vanda has responded with new rootlets. Will the top leaves lose their wrinkled appearance?
A. Courtney's night watering program is working well for me too, particularly with the vandas. I think it is just so hot during the summer that the plants dry too rapidly with only one or two morning sprays. Watering at night lets the plants absorb water over several hours. In another week or two, your vanda leaves should rehydrate and be plump and fleshy again.
Remove Salt Deposits from Clay Pots
Q. I cleaned used clay pots recently. First I clean out all the dead roots, media, etc. and rinse well. Next they go into a big tub with some bleach for about 36 hours. Next is a rinse and then refill the tub with water and cover with black plastic, done in full sun so the water gets very warm. This rinsing is done 2 times for about 24 hours each. Adding heat to speed up the dissolving process did not remove the salts. Maybe some acid added to the water will do better at breaking the salt bonds. An internet site search recommends soaking in a mild vinegar solution. I’m thinking muriatic acid. Why use a pop gun when a shotgun is available at the pool supply store?
A. Fred Clarke's advice on cleaning pots is to wash with soap and an abrasive pad to physically clean the pot and then do 2 consecutive soaks with 20% bleach solution with a disinfectant (Consan, Physan or 10% pool algaecide at 2 tsp/gal) for disease elimination. My observation is that after these soaks that total up to about 36 hrs, the salts are gone or at least the visible evidence of salts is gone. We turned to our Go-To Guy Courtney Hackney for an answer, he writes: Not all salts that precipitate into the clay matrix of a pot will go back into solution regardless of the temperature. Our water is normally alkaline and to remove stubborn salt stains, you may have to change the pH of the water to acid. Use white vinegar because it is cheap and easy to work with (stronger acids can harm you and the pot). Soak the pot overnight in pure white vinegar to remove the salt. If this doesn't work, you might consider buying new pots.
Stress Delays Normal Blooming Cycle
Q. I had a little scale on my cattleyas earlier in the year. Could this cause major delays in blooming? My nodosa and brassia types have developed bud sheaths that have been the same size now for several weeks.
A. Stress can cause a delay in the normal blooming cycle. Stress from a pest infestation, application of heavy duty chemicals, excessive winter cold or summer heat can all cause a little shock to the plant. Sometimes it takes several months for an orchid to transform its sheath to a flower and some orchids form a sheath and then take a rest before blooming. Regardless of what may have stressed them before, your plants are healthy looking and growing well now. They'll bloom for you when they are ready!
Catasetum Flowers - Male or Female?
Q. The flowers on my Catasetum Penang just opened. Are they male or female flowers?
A. Those helmeted flowers are female. The female flowers may not be as attractive as the male flowers but they last longer. The conventional wisdom is that female flowers are more likely in conditions of high light and low moisture and male flowers are more likely in shadier conditions with more moisture. Others report female flowers more common early in the blooming season and male flowers more common later in the blooming season. Female flowers are reportedly somewhat rare in cultivation and even in nature female flowers are fewer than male flowers. The plant should bloom for you 2 or 3 times this summer, maybe next time you'll get male flowers.
Orchid Root Tips Turn Brown at Edge of Pot
Q. I have a problem with many of my orchid roots and the photo of L. tenebrosa is typical. The root tips turn brown and stop growing as they touch the side of the pot or just about any other object. The problem seems to occur mostly with clay pots and the coarse potting media I purchase through the SAOS. I use the Dynamite product and apply a liquid fertilizer 2 times a month. I try to use just enough fertilizer to get to 100 ppm of nitrogen using the calculator on the SAOS website. I water heavily and flush the pots every 2 days. I grow these orchids in about 3,000 foot candles of light with a lot of air circulation from a fan. Would a reverse osmosis system solve this problem?
A. We turned to our Go-To Guy Dr. Courtney Hackney for an answer on this one, he writes: The most obvious cause is salt buildup, which is what you have already concluded. To check for this take a look at old versus new clay pots. If you get roots attaching to the new pots, but dying when they contact old pots that is a good indication that you have toxic salts built up in your pots. You do have very high conductivity and are also providing a lot of fertilizer. Dynamite provides all the nutrients you should need and increasing the salt levels of your water by adding the fertilizer may be just too much.
You are also giving your plants very high light levels, which can cause pots to get too hot and burn your leaves. If you see dead roots in both new and old pots it can be just hot pots. It is not obvious from your orchid photograph that it is salt buildup, but it may be. I have had a few of the same problems this year. What I have started doing in the summer is to water heavily as the sun goes down and then water again first thing in the morning. This allows the salts on roots and pots time to become soluble and then be flushed out in the morning.
Sunburn on Vanda Leaf
Q. My vanda is really worrying me. It has been very healthy with lots of strong thick roots. It just finished flowering and now has two new spikes starting, but as you can see in the picture the leaves are turning yellow and black. I read about the Thai disease. Could that be what is wrong with it?
A. I think the vanda leaves look like they are sunburned perhaps from being moved suddenly into brighter light. The white bleaching on the highest point of the leaves and only on one side of the leaves is where the sun scorched the leaves. The brown spotting appears to be a secondary fungal infection attacking the damaged leaves. Spray the leaves with fungicide to stop any secondary infection. The sunburned leaves will not recover their greenness, they will eventually become brown and dry and most likely fall off. The good news is over the next year or two, the plant will throw off keikis at the base of the plant that will grow into full size plants after which you can top the plant and it will be beautiful once again.
Scale on Dendrobium
Q. A dendrobium I got at the Redlands has something on it which I thought was juvenile scale. It looks like a small grouping of white lines each about 1/16 inch long arranged in a small concentric circle in 2 different places and it looks like they start where the pseudobulb is attached to the tree fern block. It was on there when I got it so I sprayed it with neem oil and later I wiped them off. Does this sound like scale or something else?
A. You are a very meticulous grower who has diagnosed the problem accurately, it is juvenile scale most likely from the inaccessible area between the tree fern slab and pseudobulb. You can spray with Bayer Tree and Shrub (1.5 tsp/quart). Spray every accessible surface and then drench the slab from behind to reach all the little crawlers. If you want to eradicate scale, Distance is the answer though it is a pricey solution at $250/quart.
Mealybugs on Cattleya
Q. I have a dusty white appearance on a couple cattleyas. Up until now, the white has always been down in the throat of the leaves (leaf axils). I am examining all the plants now and this is the first time I have been able to see anything other than a white powdery area. Are these mealybugs?
A. Correctomundo, Mealybugs are sucking insects that attack any part of the plant but tend to stay tucked away at the junction of leaf and stem. Severe infestations cause chlorotic areas to appear on the leaves, which may darken, causing the leaf to yellow and drop prematurely.
If there are only a few mealybugs, use a Q tip dipped in isopropyl alcohol or toothbrush dipped in a pesticide like Malathion, Orthene or Safer Soap (used per label instructions) to physically remove the mealybugs or put isopropyl alcohol in a spray bottle and spray the mealybugs. For more severe infestations, apply the pesticide and repeat the application 2 weeks later. Be sure to spray all plant surfaces, particularly the undersides of leaves and leaf axils.
Protect Phalaenopsis Buds from Katydids
Q. How do I protect the buds of phalaenopsis orchids from katydids? I would like to keep my orchids on the screened-in porch this summer but invariably a katydid gets in and destroys the buds. Is there any help for this?
A. How about a shoe? Seriously, there is nothing you can do except kill the katydids before they eat the buds or move the plants inside when buds start to form. Maybe it would be possible to put some sort of mesh over the buds. Katydids can be tenacious and love developing stems and buds because they are soft and full of nutrients.
Dunk Plants in Bucket to Fertilize?
Q. I keep a bucket filled with fertilizer solution and dunk my plants in the bucket after watering them. I change the mix every week. Is that good or bad?
A. You run the risk of transferring diseases and/or pests from plant to plant by dunking each pot in the same bucket of fertilizer. I think the most efficient use of fertilizer is to water your plant first and then come back a half hour later once the velamen is wet and open and then add your dilute fertilizer solution to the pot. Some folks with just one or two vandas have a bucket for each vanda and dunk the vanda in its own bucket.
photos by Greg Allikas
Honeydew on Orchids
Q. Can you tell me what the secretions are that some orchid plants put out around the stems of their flowers? Sometimes it is sticky and develops sooty mold like on Grammatophyllum scriptum. On other orchids, such as Oncidium Sharry Baby, it is more watery. I find it seems to appear in the morning.
A. The secretion is simply plant sap, called honeydew, which is secreted by healthy plants. It is, as you note, basically sugar water, and can lead to sooty mold. This is why sooty mold can often be an indicator of sucking insects, which feed on this same sap, supplied to them by the plant’s osmotic pressure. When the pressure is sufficiently high, the sap passes right through the bug's digestive systems, resulting in conditions favorable for sooty mold. - by Ned Nash, courtesy of the AOS
Cleaning Residue from Orchid Leaves
Q. I purchased a mature Vanda with 3 large keikis. It looks like the plant didn't bloom regularly. The lower leaves are covered with algae and dried fertilizer. I tried washing them off with a soft toothbrush with no success. Is there a product to remove this residue?
A. I think there are several points here that need clarification. First, there are lines of vanda breeding that produce large plants that may be naturally shy blooming. I doubt that the leaf deposits that you cite are responsible for the poor flowering record of this plant. More probably, it is that the plant was in a position in the grower’s greenhouse where it did not receive enough light or it is of the shyer blooming type. Second, it is possible the leaves are beyond being cleaned easily. Other methods worth a try are lemon juice and one of the new horticultural oils such as Sunspray. Too much scrubbing may damage the leaves. Personally, I look at overlarge plants of any type with some skepticism, especially if they have what appears to be a poor blooming history. - by Ned Nash, courtesy of the AOS
Erwinia on Paphiopedilum
Q. What is going on with this plant? We just got it at the JAX show a few weeks ago, and the leaves all of a sudden began to look like leprosy. Any ideas?
A. That is a sick puppy, probably a bacterial infection caused by Erwinia known as Bacterial Brown Rot. That bottom leaf looks pretty bad, I would cut it off with a sterile single edged razor blade. Then decide what to do with the top leaf, perhaps treat the plant and then watch the spot. If the spot continues to enlarge, cut if off one inch below the obviously infected area and treat again. To treat, you can pour hydrogen peroxide on the infected parts or better, spray with Physan, Consan, or 10% pool algaecide (2 tsp/gallon) or best spray with a copper compound like Kocide (1 tbsp/gallon). But pour peroxide on it until you locate the other chemicals. The bacteria are spread by splashing water, so you may also want to disinfect the area 2 ft or so around the plant.
Repot Just Before New Roots Emerge
Q. I am through with ‘over wintering’. Most of the plants have great color and some are showing new growth but not much in the way of new roots. Is that what I should expect after this cold winter. I am tempted to repot many but remember hearing that one should not repot if there is no new root growth.
A. You should be seeing lots of new root growth on your cattleyas. It is best to repot when those new roots are less than ½ inch long. If they are longer than that, they will likely be damaged during repotting and if they are less than 4 inches long, the root will not rebranch and continue to grow. The unifoliate cattleyas (single leaf above the pseudobulb) are much more forgiving and can be repotted anytime.
The bifoliate cattleyas (double leaf above pseudobulb) are much more susceptible to transplant shock so you should wait for the roots to just begin to emerge before you repot. Wait until your phals are done blooming and plan on repotting them annually in the June/July time frame. Dendrobiums do not like their roots disturbed so repot them only if the potting mix has deteriorated (soft and feels like dirt) or they absolutely can't go another year in the pot. (Apr-10)
Black Rot on Vanda Keikis
Q. Today a Vanda keiki turned black where the keiki attaches to the lower part of the plant. What is this? The rest of the plant and the four other keikis are green and happy.
A. That is black rot, very deadly and fast killing. Get a sterile tool and cut away whatever is left on the plant to the base of the keiki and then pour some hydrogen peroxide on the wound. You'll never know whether it was caused because it had water accumulating in the new growth or it has just been this funky fall and winter. Banrot and Subdue are more powerful chemicals to combat rot although they are also more toxic with more side effects.
Aerial Roots on Phalaenopsis
Q. I bet a bunch of us have these 4+ year old phals that have roots growing up instead of downward. Totally gorgeous, healthy roots, but the plant looks like a freak. These are not keikis and the plant is not rootbound, just roots growing against gravity. How do you repot these monsters? It can't be buried that high up, won't the plant suffocate? Should the wild upward roots be removed if the plant has a healthy rootball or just enjoy it as is?
A. Do not worry if your phal has aerial roots, phals just seem to have fun with their roots growing every which way. Enjoy your plant until it has bloomed out. By the end of June, it'll be time to repot all your phals (except those summer bloomers). Phals are monopodial and grow upward rather than horizontally along a rhizome the way cattleyas do. Every year they'll add one or two or maybe three leaves on the top of the plant and lose one or two leaves on the bottom of the plant.
The bottom of the plant (the stem and roots) will gradually die but new growth continually forms at the top of the plant. So when your phal is bloomed out, you'll cut away all the dead stem and root material at the base of the plant until you reach vibrant tissue. You'll repot your orchid while it still has enough of the growing season to reestablish and gather strength for next year’s bloom.
Microfungus or Phalaenopsis Chlorotic Spot Virus
Q. I asked Tom Nasser what caused the spotting, he told me to be afraid, very afraid. He said it is a microfungus, apparently a fungus with a virus attached to it. After a little research, it may be a Potyvirus, Phalaenopsis Chlorotic Spot Virus. It is very infectious and can destroy an entire greenhouse in short order. Tom said that the microfungus likely has spread to other sections of the leaf or nearby plants and the chlorotic spotting may not yet be visible.
In the order of appearance, the leaves display yellow chlorotic spots, then more defined yellow spotting that can grow into elongated yellow streaking, then pitting, and finally large areas of grayish tissue collapse. It can be confused with mesophyllic cell collapse caused by watering with cold water, although this weathers to dark rather than light sunken spots in phals. Paph infections weather to darkish sunken spots. Tom recommended that infected plants be destroyed and the remaining plants treated with the copper fungicide phyton 27, a chelated copper fungicide that permeates the leaf more effectively than the more available copper fungicide Kocide.
From Bob Gordon Culture of the Phalaenopsis Orchid: "sometimes a condition prevails that is caused by a systemic infection of microfungi. As there are literally hundreds of these, the symptoms vary from plant to plant.
Some of the more common are a spotty, ill-defined chlorosis; a streaky chlorosis beginning at the edge of the leaf where it looks as if the leaf edge had been burned with a match or candle; a red-brown coloration appearing at the apical third or half of the lower leaves followed by a dehydrated and senescent (old) appearance and also mesophyll tissue collapse where deep pitting becomes apparent on the surface of the leaves. This latter condition can also be caused by cold water and by virus infections. However, in the latter instance, the pitting is usually dark-brown to black in appearance rather than the white to light fawn caused by fungi."
Deciduous vs. Evergreen Dendrobiums
Q. How do you know if a dendrobium is a nobile dendrobium? Is it due to the cluster of flowers as opposed to elongated spikes? Are nobile dendrobiums subject to different winter watering habits? If so, what keeps them happy? Are Den. lamellatum, bracteosum or purpureum nobiles? Do these need special winter care besides bright light?
A. Dendrobiums are a huge, diverse group of orchids that grow under a wide variety of conditions, so there are no simple cultural guidelines that apply to them all. In spite of their habitat variability, there are several common rules to good culture from Dendrobiums Demystified courtesy of the AOS:
- Use the smallest pot possible, do not overpot this genus
- A well-drained potting mix promotes good root growth and minimizes breakdown
- Most do not appreciate root disturbance - repotting can lead to shock
- No fertilizer for most species Halloween through Easter
- Hang tall plants to control top heaviness or place small pots inside much larger pots and weight down with rocks
- Do not use copper based fungicides with dendrobiums
- Repot only when roots start to grow (usually spring) so re-establishment is fast
In addition to the common rules, the whole genus can be broken down into 7 or 8 general groups with similar culture, the key being in their winter dormancy requirements. Check out Dendrobium Culture
and books in the SAOS library for more information.
To answer your specific question, Den. purpureum and bracteosum are Pedilonum section dendrobiums and Den. lamellatum is a Platycaulon section dendrobium. Both types like to be a little drier in the winter but do not like to dry out completely. Restrict fertilizer during the winter, but otherwise treat them like your cattleyas giving them bright light and watering once every 7 to 10 days.
The nobile dendrobiums are mostly pendulous and deciduous and they bloom from leafless canes in the spring after they have been given an extended dry, bright winter dormant period.