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Treating Orchid Pests and Disease

For your orchids' sake, I hope you won't ever need this info., but here it is anyway - just in case.

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treat spots on orchid leaves

At one time or another, all orchid growers will have to treat orchid pests and disease. Find out how to identify problems and what action to take. The good news is that bacterial infections and pests are usually not serious and are easy to treat. 

What you’ll learn: how to treat orchid pests and disease, including: bacterial and viral infections as well as pests such as scale and mealybugs.

While attending an orchid show at the Red Butte Garden in Salt Lake City I was warned the bacterial infections are quite common on orchid leaves. I was reassured to learn that these infections are also easy to treat. Sure enough, it wasn’t long until the tell-tale black spot showed up on my orchid’s leaf. Luckily, I knew what to do.

This-totally-worked-the-black-spots-on-my-orchid-leaves-are-gone - treat orchid pests and disease

The First Line of Defense is Prevention

4 Tips for Preventing Disease

  1. Buy healthy plants.  Before making a purchase inspect leaves for reddish-brown to black spots. Do not buy plants with spotted leaves (like those in the above photo). 

    Choosing an Orchid

    Winning Strategies

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  2. Provide air circulation.  Orchids love humidity, and so does bacteria.  To prevent diseases that thrive in a humid environment, turn on a fan. Air circulation will do wonders in preventing bacterial growth. 

    Temperature + Air Circulation = Healthy Orchids

    These tips will help your orchid bloom and avoid bacterial leaf spots.

    Read
  3. Avoid over watering.  Besides killing your orchid’s roots, standing water is like sending an invitation to unwanted bacteria to come live in your orchids. 

    Watering Orchids: Find Out What Works

    Learn how to water correctly and you'll avoid the #1 cause of orchid death

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  4. Isolation.  As an extra precaution isolate new plants for a week or two, just to be sure that it didn’t bring any hitchhikers, in the form disease, along. This advice has saved my orchids. Sometimes we may overlook bacterial spots, that somehow become glaringly obvious once at home.

Identification

If you do notice something unusual, the first step is to identify the problem so that you can apply proper treatment.

Treating Black Spots on Orchid Leaves

Bacteria can be identified by a reddish brown, or black spot on the orchid leaves.  The spot may be quite tiny, like little freckles sprinkled on the leaf, or larger, with a lighter ring around the edge.

Hydrogen Peroxide

Full strength hydrogen peroxide can be used and will kill the bacteria that causes black spots on orchid leaves.  Simply soak a Q-tip with hydrogen peroxide and dab affected area(s). Avoid swabbing underneath the leaf, as this may kill the leaf. (Having bathed the underside of an orchid leaf in hydrogen peroxide, I know the truth of that statement.)

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Cinnamon

Another, or additional, option to treating black spots on orchid leaves is to make a cinnamon paste.  Cinnamon possesses antibacterial properties, making it a natural choice to treat bacteria. Plus, it’s something that’s on-hand. Mix powdered cinnamon with water until it forms a paste consistency.  With a Q-tip, swab the paste onto the affected area. Once again, swab just the topside of the leaf.

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Cut it Off

Trimming off the affected are with a pair of sterilized scissors is another option.  To sterilize scissors, wipe them down with a cotton ball soaked in rubbing alcohol. When making the cut, be sure trim about 1 cm. past the black spot.  If the entire leaf is affected, cut off the whole leaf at the base. The black spot on the below leaf was quite large and near the crown of the orchid. I trimmed the entire leaf off as close to the crown as I could.

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Identifying Sunburn

I am including a photo of an orchid leaf with a sunburn so that you will be able to distinguish a sunburn from a bacterial black spot. Note the rosy tint and the light yellow leaf color. The only thing to do here is to move your plant a little further from the window 🙂

sunburned-orchid-leaf.png

Virus

This is the bad news: Viruses can be difficult to diagnose and almost impossible to cure.  Viruses can be identified by a color break in blooms.  The best course is to throw out such plants. If you don’t want to throw out your orchid, keep it away from your other plants. Use caution and keep all tools (watering cans, razor blades etc.) away from the infected orchid. If you do use a razor blade, be sure to throw it out after use.

Now You’ve Got Black-Spot Removal Know-How

Now that you know what those little black spots are, you are ready to take action if ever the need arises. Black spots on orchid leaves are easy to treat and can be taken care of with items you probably already have on hand, no need to run to the store. Just for the record, I have had more success with treating black bacterial spots with hydrogen peroxide than I have with cinnamon.

Pests: Mealybugs and Scale

Just the words scale and mealybugs give me a shiver of distaste! These little beasts can easily spread throughout an entire collection if you’re not careful. The first step is to identify these bugs. If you notice any sort of pest, immediately remove the orchid away from the rest of your orchid collection.

Mealybugs

If you notice a cottony, web-like substance around the base of the plant on psuedobulbs, rhizomes,  or on the underside of leaves you may have mealybugs. Another tip-off is the presence of ants. Mealybugs excrete honeydew that attract ants. 

Scale

Scale, particularly armored or boisduval is considered the worst of orchid pests. Unlike mealy bugs, you can’t simply use your fingers to brush the scale away. The scale has a thick detached shell that is practically cemented to the orchid. Look on leaves, and all around the base of the plant, for signs of this pest. Scale can be difficult to get rid of because they hide in every imaginable nook and cranny. Repeated treatment is recommended.

Identifying scale: Hard light, brown bumps that you can not scrape away indicate boisduval scale.

Treatment for both mealybugs and scale:

  • First, isolate these orchids from the rest of your collection.
  • Second, spray plant with horticulture oil. This is most effective when bugs are in the nymph phase.
  • Third, with an old toothbrush and 70% rubbing alcohol, and a pair of surgical gloves scrub every nook and cranny of your orchid. This may seem overwhelming when you first look at your orchid, especially of your orchid is large, with lots of leaves and pseudobubls, but you can do it. Once you get started, it’s not so bad.

I recommend pouring a small amount of rubbing alcohol into a dish so that you can easily dip the toothbrush into the bowl without contaminating the rest of the alcohol.

orchid pests - scale

The orchid leaf of this Miltoniopsis orchid is covered in Boisduval scale.

treat orchid pests - scale

Materials needed to treat scale and mealy bugs: 70% rubbing alcohol, a small dish to use to hold alcohol, toothbrush, surgical gloves..

treat scale and mealy bugs

Dip the toothbrush into the dish with alcohol and scrub every nook and cranny of the orchid.

Keep the toothbrush and alcohol on hand so that you can repeat the process every 10 days, or sooner, if you see signs of the bugs. After scale has been treated the hard shells will dry up and easy flake off, though a scar will remain.

If you suspect that pests are down in the orchids roots and soil you can safely pour hydrogen peroxide in the potting mix. As this will dry out the roots, be sure to water thoroughly water afterwards.

Bugs Are No Fun-But Are Treatable

Bugs are a huge nuisance, but you can take action against them. As soon as you notice them, begin treatment right away. As always, an ounce of prevention is worth a pound of cure: Check new plants for sign of pests before purchasing. Keep new plants away from other plants until you are sure the plant is healthy and pest free.

Now you know how to treat orchid pests and disease. I have confidence that you’ll be able to with the tools we’ve talked about you’ll be able to successfully eradicate these common pests and disease.

Check out my EBOOK: WHAT TO DO WITH YOUR GROCERY STORE ORCHID to learn how to care for you Phalaenopsis orchid.

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16 Comments
  1. maya Hira says:

    where can I get this house happy orchid, without going to nursery.they very expensive in nursery.

    1. Anna says:

      Maya,
      If you happen to have a Trader Joes nearby you can find a selection of orchids at a good price.
      Anna

  2. Anonymous says:

    Many thanks for all your tips. Barbara

    1. Anna says:

      Your welcome Barbara! I’m always glad to help.
      Anna

  3. Jeremy says:

    Hello my Orchid was very healthy and now it is developing black spots. I think my moisture level might have been to high. Would anyone be willing to look at a picture of the plant and add any advice?

    Cheers

    Jeremy

    1. Anna says:

      Jeremy,
      Turning a fan on low, will help prevent bacterial growth on the leaves by adding some air circulation.
      Check out this post for more information:
      https://www.orchidbliss.com/temperature-air-circulation/
      Also some varieties, Oncidiums come to mind, are particularly prone to black spots.
      Email me at anna@orchidbliss.com, I’d love to see a picture of your orchid.
      Anna

  4. Sandi says:

    Where can I find horticulture oil? Speciality store or big box in garden section? Thanks you!

    1. Anna says:

      Sandi,
      I purchased my horticulture oil through Amazon. Here is a link for the oil that I purchased. At no additional cost to you, I will receive a commission if you purchase through that link.
      Horticulture Oil
      I’m so sorry that you are in need of horticulture oil!
      Best of luck getting rid the pests tormenting your orchids!
      Anna

  5. Sinead Louise O'Sullivan says:

    Help!! Never had much luck with orchids and my mum brought me one for mothers day. I inspected the plant the next day and noticed miuld/algae in the pot. The roots still look mostly green but I have noticed on the underside of some of the leaves are some little black mouldy looking spots….not much but enough to worry me. My orchid is in bloom and still has buds so from what I have read they say to avoid replanting. Help….don’t want to loose another one. Do I replant or just treat the algae.

    1. Anna says:

      Sinead,
      Thanks for reaching out. There is an easy fix to getting rid of mold. Apply a bit of hydrogen peroxide, lemon juice or horticulture oil to the mold. Wait a few days and reapply as needed.
      Anna

  6. Jennifer says:

    I have a orchid that was given to me by my next door neighbor who was moving. I noticed this white stuff on the leaves and stems. Any idea what this could be. Its a old orchid

    1. Anna says:

      Jennifer,
      Could you send me a picture? Email me at: anna@orchidbliss.com.
      I’m happy to help you figure this out.
      Thanks,
      Anna

  7. Katiusca Gonzalez says:

    Hola, buenas noches, quisiera enviarte unas imágenes de cuatro de mis orquídeas, las cuales presentan una infección y realmente no se que es, y necesito ayuda, que tengo que hacer para poder mostrártelas? g
    racias

    1. Anna says:

      Katiusca,
      To send me images, email me at anna@orchidbliss.com
      Thanks,
      Anna

  8. Jennifer says:

    I emailed you 3 pictures. Its a very old orchid. She had it outside one her fince for many years.

    1. Anna says:

      Jennifer,
      Thanks for sending me the pictures. Check your inbox for my reply. Pictures are always helpful.
      Have a great day,
      Anna

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START HERE to Learn More About Caring for Orchids

Find Out What I Wish I Knew When I First Started Caring for Orchids

YES! THANK YOU!