Orchid Pathogens

Before we start on orchid pathogens, keep in mind that orchids are sensitive plants. If an orchid is well taken care of, it will be strong and thus have high resistance against pathogens. Regular routine of feeding, watering and chemical application on the plant will help keep pathogens away. So take good care of your orchids and in turn they will flower well for you.

Most of the time, one disease can lead to another in a cascading effect if the primary issue/disease is not taken care of. Growing orchid takes a lot of care, observation and dedication.

Bacteria / Fungal Ailments

Browning due to over-watering

Browning due to over-watering

Brown Spot

Brown spots can be caused by mechanical injury to the plant, over-watering and mechanical pest attacks. The ruptured epidermal layer of the orchid leaves provide wet substrate for opportunistic pathogens to colonize.

To remedy, first apply fungicide to the brown spot to prevent fungal growth. If the fungal/bacteria growth continues spreading, cut off the infected portion of the plant. Dip the cut portion in fungicide, dry it before transplanting it.

Burnt black/ash spot with secondary bacteria infection

Burnt black/ash spot with secondary bacteria infection

Black/Ash Spot

Black spots are usually due to chemical burns. When mixing your fertilizers, fungicide or pesticide. Ensure that mixing is done well in a container before applying them to the plants. Uneven mixing can result in crystals burns during hot afternoons resulting in small black spots on the leaves.

Black spots may also happen due to too much sunlight. Orchids are picky plants, always remember to provide yours with the right amount of sunlight for the type of orchid that you are growing. If an orchid leave starts turning yellow, this might be due to too much sunlight, provide the plant with some shade and the leaves should turn back to green. Prolong period will end up in burnt spots. Burnt spots can result in further chemical burns as the innards of the plants are exposed on the edge of the burns when treated with chemicals. If fresh burnt spots are kept wet due to rain and watering for prolong periods, secondary bacteria infection can set in.

Basal root rot

Basal root rot

Root Rot

Root rot occurs due to incompatible basal media or over-watering. This usually happens for epiphytic orchids (e.g. Dendrobiums) as they grow naturally on trees and thus their roots should never be waterlogged.

Root rot also attracts opportunistic microbes and subsequently snails and slugs as the wet substrate provides a good meal for them.

Stem rot

Stem rot

Stem Rot

Stem rot usually occurs from bottom up from root to stem to leaves. This happens when root rot is not remedied and occurrence increases with secondary pests such as snails and slugs sucking sap out of the soft fleshy tissues colonized by bacteria/fungi.

Secondary fungal/bacterial infection by a different type of pathogen may also occur after the initial colonization. This is common for badly neglected orchids.

Crown Rot

Crown rot usually occurs from waterlogged crown. When watering orchids particularly Vandaceous types, always take note not to allow water retention in the crown. This is also why we frequently advice our customers to water their plants during the morning rather than in the evening as water in crown will dry up in the afternoons.

Crown Rot

Crown Rot

Vandas with crown rot will stop growing vertically as the apical meristem has been damaged. It is advisable to perform a top cut below the rot to produce keikis from the axillary buds if you wish to salvage the plant.

Mechanical Injury

Movements in your garden due to children, pets or even yourself can caused damage to orchid leaves unknowingly particularly for terrestrial orchids (e.g. Vanda). The exposed areas from the broken leaves will be susceptible to bacteria/fungal infection.

Mechanical damage to orchid leaf due to pet movement

Mechanical damage to orchid leaf due to pet movement

Mold/Soot

Mold or sooty black fungi may grow along basal axillary joints between the stem and leaves of Vandaceous orchids, commonly due to accumulation of water in these axillary joints. This is usually not serious if the epidermal layer is not damaged. The mold/soot can be easily wiped off with a cloth dabbed with very diluted detergent to clean up the leaves. However, if left for prolong periods, this may result in epidermal necrolysis and develop into similar condition as described for crown rot.

Other factors

If you have other plants grown within your garden, e.g. this banana tree, you may have more problems with pests like snails and slugs.

Banana leaf

Banana leaf

Snail

Snail

 

 

 

 

 

 

Basic remedy for damaged plant parts

  1. Cut off the infected portion of the leaves, stems, roots or pseudobulb and discard them.
  2. Wash any remaining dirt off and dip the plant into fungicide (e.g. Thiram).
  3. Leave the plant out to dry off the fungicide before transplanting the plant.
  4. Observe. If root rot occurs again, you probably didn’t remove the infected portion of the roots or treat the plant properly.
  5. Repeat process if required.

 

Orchid stem infected with Ringspot Virus

Orchid stem infected with Ringspot Virus

Viral Ailments

The main virus that affects orchid are Cymbidium Mosaic Virus, Cymbidium Necrotic Ringspot Virus, Tobacco Mosaic Virus and Odontoglossum Ringspot Virus. Infection can be very common in Dendrobium and Oncidium orchids in the tropics. This virus is transmitted from cell to cell through their plasmadesmata and impedes the orchid from growing properly. The virus forms a distinct circular pattern on the orchid leaves.

When the virus spreads dominantly across the leaves, they will start to yellow and die off together with the virus.

Dendrobium Ringspot Virus

Dendrobium Ringspot Virus

This infection is usually a considerably slow process as compared to bacterial/fungal infection, especially if the plant is well taken care of.

It is not possible to completely rid the orchid plant of viruses; however the infection can be gradually contained in young plants. Notice in the first picture that this virus is more prevalent on the older leaves. This virus replicates itself in the cells of the orchid leaves and gradually gets transmitted to newer leaves.

To contain the virus in a young plant, simply strip off all infected leaves by pulling them downwards or making a clean cut at the base of the leaves. Dip the plant in fungicide to prevent any fungal growth and allow the plant.

 

Infected orchid leaves pulled off

Infected orchid leaves pulled off

New leaves produced will be more resistant to the virus. Continue removing any infected leaves overtime as the plant grows and the prevalence of the virus will gradually decrease. This can be a long process but if done correctly, the viral infection will be kept low gradually.

The virus will lay dormant in strong plants and may surface again as the plant senesce. Plant resistance, similar to human, grows weaker over time as it accumulates damages, diseases and infection throughout its growth. However, do not fret when your orchid gets old. You can always produce keikis or produce seedpods from them to have new orchid plants for growing again.

Mutated mokara orchid with variegated leaves

Mutated mokara orchid with variegated leaves

Genetics Ailments

As the name suggests, genetic ailments can never be corrected. Not all genetic mutations are bad, those that results in the plant having slower growth, lousy flowers and disease prone are bad. Sometimes in genetic mutations can produce beautiful effects like Dendrobium Liberty Mutation, splashes on the petals and petal fusion that results in rare prized collectible orchids.

Common Insect Pests

Insect pests that affect orchids include spider mites, thrips, slugs, snails and midgets. These are large pest, that can be easily observed and removed by applying insecticides.

Spider mites, also commonly known as red spiders, hide on the underside of orchid leaves and suck sap out of its host. Severe pest infection can result in dwarf plants, reduced in flowering and small and deformed flowers due to their feeding on the plant’s sap. This pest spreads fast and can be persistent.

Thrips and midgets are common pest for Dendrobium orchids. These insects use the buds of orchids, particularly Dendrobium to house their eggs. When their young hatch, they feed on the sap of the plant from within the buds, resulting in the buds falling off prematurely or having poorly formed flowers. Thrips/midgets can be killed and warded off using pesticides such as Imidacloprid.

Slugs and snails feed on wet substrates of the plant. Aside from being secondary pest after primary plant infection by microbes, snails/slugs are also common after a heavy rainfall. The Oncidium and its alliance are particularly vulnerable to snails/slugs after rain due to their soft petals. After heavy rain, often the soft lips of the Oncidium flowers will go missing where snail/slugs are rampant. Snails/slugs can be remedied by throwing snail/slug pellets (molluscicide) around the vicinity of your orchid. These molluscs will dissolve into liquid with a uric smell upon consuming these pellets.

Moult left behind by emerging butterflies on orchid stem

Exuviae left by emerging butterflies on an orchid stem

Caterpillars can also appear on poorly maintained orchids. Caterpillar attacks the flowers and soft chewy parts of the plant, e.g. the crown or spiny tip of a Vanda teres. This can end up with parts of the leaves dying and drying up as the sap were sucked out by the caterpillar or flowers damaged. Caterpillar eggs are usually laid on the underside of the leaves as it provides shelter for them, and also making them not easily visible. Where infestation is low, caterpillars can be removed manually using a pick or pointy petiole of a leaf to transfer instead of killing them with pesticide. Personally I don’t think caterpillars are that bad for private garden as they will moult and change into a beautiful butterfly later on. =P

Precautions for Treatment

  1. After using an orchid shear to cut off infected portion, remember to sterilize it by flaming the blades with a lighter, dipping in fungicide solution etc before cutting the next piece to reduce transmission.
  2. When cutting off infected portions, always cut an extra bit more of the healthy plant so as to ensure that the remaining portion will never be incontact with the infected portion.
  3. Be careful not to damage other plant parts with the sharp edge of the scissors, open wounds are susceptible to infection by microbes. Expose areas should always be minimize and treated with fungicide where required.
  4. Never use old media for transplanting as it’s likely to be contaminated.

32 Responses to “Orchid Pathogens”

  1. Hi,

    May I know how to get rid of spider mite?

    Thanks,
    Nwe

  2. Hello Nwe,

    You can get rid of spider mites by spraying miticide on the orchid leaves. Most spider mites will reside on the bottom side of the orchid leaves, thus if your orchid is infected with spider mites, always remember to spray your miticide on the underside of the leaves.

    Cheers
    silverelf

  3. Could you recommend a miticide that you sell? Does Malthion

    kill Red Spider Mites?

  4. Does Malathion 84.3% kill spider mites? How about Dimethoate or

    Diazinon? Which do you sell and what’s the price. I read that

    Kelthane is very effective but was banned from usage in Singapore.

    Is it true?

  5. Dear Mr Teo,

    The miticide that we use are in commercial packs for farm use.
    At the moment, we do not sell miticide or other chemicals but will look into this as, like you, many customers has requested for them.

    Yes Malathion eliminates red spider mites. For a non toxic alternatives, you can use summer oil instead. Its ecologically friendly and has minimal toxicity to human. You should be able to get these in horticulture section of supermarkets like NTUC and cold storage.

    silverelf

  6. Hi Mr Teo,

    Apologies for the belated reply.
    Yes the chemicals that you’ve mentioned are all pesticides.
    Kelthane is probably banned as DDT is one of the intermediates used in its production.
    DDT is banned due to several reasons, you can read more on wiki here: http://en.wikipedia.org/wiki/DDT
    We do not sell chemicals at the moment but they can be easily purchase from supermarkets near your home.

    silverelf

  7. I spray fungicide after every rainfall, even if it meant everyday.

    Is this correct because I feel that once the residue on the leaves

    has been washed away by rain the plant is exposed to pathogenic

    attack.

  8. I spray fungicide after every rainfall even if it meant everyday. I

    feel that once the residual powder is washed away, the orchid plant is

    unprotected against fungal attack. Is this reason to spray the chemical

    correct?

  9. Hi Mr Teo,

    Yes that is the correct method. You can also add neem oil/white oil to your fungicide as it helps to adhere to the plant surface.

    silverelf

  10. My orchids are always exposed to the elements. I don’t have

    a place to prevent rain from destroying their roots.

    So, what should I do to compensate for the root destruction?

    How does one go about saving them if rainfall is too frequent?

    Thanks!

  11. Hi Silverelf, firstly like to thank you for such informative site for orchid lovers! Most relevant to me since I m from Singapore too.
    Need advice abt my Vanda. I got one abt 3 weeks ago and everything seems fine with all buds flowering. Suddenly 1 leaf (7th from the crown) turn splotchy and yellowing almost overnight, much like an over ripen banana. All other leaves are fine. I had snipped it off in case it spread. That leaf was still firm to touch. I have fertilised the plant twice so far with 63 sprayed lightly on whole plant.
    If there is a way I could attach a picture…

  12. Hi Wong,

    Its okay to snip off the leaves.
    Its probably due to mechanical damage.
    The leaves may have been accidentally folded or damaged resulting it to turn yellow. The plant will still grow but aesthetically, it may not be as nice looking as with full leaves.

    You may also do a top cut the orchid above the damaged leaves if there are roots and replant the orchid so that it can grow new leaves but this is not required.

    silverelf

  13. Hello silverelf:

    How could i control these kinds of snail are eating the rooting system of my dendrobium. Their very voracious feeders. Can please recommend any chemical application. Im leo from the southern part of Philippines. Can anybody out there dare to give comments and advices.

  14. Hello Leo,

    You may control them by applying snail pellets around the perimeter of your orchids.
    The snails and slugs will go for these pellets instead of your orchids. =)

    Apply this over a period of 3 months and you should be able to get rid of most of your slugs and snails.
    You will need to get small pellets for small snails and big pellets for larger ones to be more effective.

    silverelf

  15. Hi silverelf, may I know how to treat black rot on cattleya’s new lead? Should I cut it off? Thank you, Isaac..

  16. Dear Isaac, you can use fungicide to treat them or if serious cut it off. There in a page in our website for Orchid care, https://tohgarden.com/orchid-care/common-orchid-pathogens/

  17. How often should I use fungicide or pesticide on orchids?
    How do I apply them?
    Appreciate your advice. Thank you.

  18. Hi Tracy,

    Once to twice a week will be sufficient.

    silverelf

  19. Hi silverelf, I just discovered that under the leaves of one my outdoor hanging dendrobium are many silverish-white regions, although I don’t see any insects per se, nor any webs. There are small, black “sediments” on the underside though, but non-moving. Then I notice there are similar white regions, but much smaller, on the underside of other dendrobiums nearby too. If I could post some photos it might be clearer.
    Do you have any idea what the problem is and how to treat it? Thank you!

  20. Hi Lynn,

    The white silverish region you observed may be fungicide residues that adhere to the leaves, those are not insect webs. We use fungicide with summer oil to adhere them to the leaves of the orchids. This protects the orchid plant from fungal growth. You may send pictures to [email protected].

    silverelf

  21. Hi silverfish, my orchid collection has been ruined by crown rot. How could such rot be controlled when our orchids are left in the
    open exposed to rain. Could spraying fungicide stop the nuisance?

  22. Hi silverfish, I have thrips problem in my small orchid nursery. I spray insecticide (decis n malathion), once every 2 weeks and I rotate them. But somehow only some of the thrips die and many still survive and multiply very fast. Do you know whats the best way to control this infestation?

  23. Hi Eric,

    Increase the frequency of the insecticide spray to twice a week.
    That should solve the problem.

    silverelf

  24. Hi Silverelf, what fungicide and pesticide (systemic) would you recommend?

  25. Hi Juli,

    We use Thiram and Imidacloprid.
    There are quite a number of options for fungicide and pesticide available locally.

    silverelf

  26. Hi Silverelf,would you recommend a cure for Fusarium,i’ve lost 3 vandas to it.It started with the base of the leaves turning brown while roots were still white, firm and fine,then stem started to turn brown and even the green leaves starts to shiver. I tried to save it by cutting upwards where the stem still green but it did not work at all.Thank you.

  27. Hi Ms Ong,

    Try applying some fungicide to treat the Fusarium first.
    Apply the fungicide and let the plant dry out so that it kills the fungus.

    silverelf

  28. Hi Silverelf,
    Will Captan (Horti) works? i read online to use ‘Daconil or Cleary’s 3336’ but i cant seems to find any of these in S’pore.I’ve even tried cinnamon oil and need oil but is not working and is spreading fast to my other orchids

  29. Hi Silverelf,
    Will Captan (Horti) works in treating Fusarium as i cant find any Thiomyl WP 50% in S’pore, recommended from the internet. I’ve even tried cinnamon oil and neem oil, none is working.

  30. Hi Ms Ong,

    Captan is a pesticide not a fungicide.
    Try using a fungicide instead to cure the fusarium fungi.
    Allow the plant to dry out after application.

    silverelf

  31. Hi silverelf, part of my orchid plants leaves suddenly turned white. Some leaves turned white in between leaving both ends still green. Some about 3/4 of the leaves from the tip. Can the cause be of spraying of insecticides?

    ckh

  32. Hi ckh,

    Yes, it’s possible due to concentrated chemical burns.
    Make sure that you’ve diluted the chemical as specified on the bottle.

    silverelf

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