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Plant Diseases and Pests of Orchids


Before I get to telling you about plant diseases and pests of orchids, let me tell you a story.  One day I was at a local box store and found their discount plant material.  As I picked through the plant material I found a treasure.  This treasure was not just one but two. What was it?  Well, it was two orchids.

The first orchid looked wonderful.  The leaves were healthy, green, and the blooms were colorful and fresh but…..the other orchid looked sad.  Frankly, I am a sucker for an underdog and this plant seemed to be an underdog that had been cast aside without a care.  In doing so, I could not just buy the healthy one.  No, I had to get both.  I knew I could “save” the sick orchid or I thought.

While I am very familiar with plant disease and pests, I never took the time to really and I mean really examine the new plant material.  So, when I got my plants home, I watered them and placed them in their new home.  Oh, I was so excited.  The two new plants fit in perfectly with the other orchids I had but…….all my excitement disappeared a few days later.

The morning started off as usual.  I turned the computer on and got to work but I noticed a few ants on the plant stand where I had the orchids.  When I got up and walked over to the planters, I knew what the problem was and I had brought it into my home.  What was this pest?  Well, it was aphids with their little ant helpers.  While I am going to be talking about aphids and orchids later, the story above is a cautionary tale.  It does not matter what plant material you may be purchasing, always make sure it is plant disease and pest free.  Never feel that you can save the plant along with money.  I promise you, this never really works out. 


Aphids are truly little suckers and when I say suckers I mean they suck on the plant to harvest the plant’s juices.  These little insects feed on new growth, buds, flowers, and on the underside of leaves.  As they grow, they will drop their white skins, which can be seen on the top of leaves. 

Another sign that you have an aphid problem is the sight of honeydew or sooty mold.  The honeydew is a sticky substance that can be seen on leaves and stems.  This honeydew is created as a byproduct of the aphids eating.  As honeydew appears on the leaves, so does the sooty mold, which grows on the honeydew.  This sooty mold can be seen as a black substance on the leaves.

The final way to tell if you have aphids is the appearance of ants.  Ants love the sweet tasting honeydew.  In exchange for the honeydew, ants take care of the aphids. 

If you find that you have aphids, the best approach is to get rid of the ants.  This must be done completely to eliminate the aphids without chemicals.  To do this, place sugar based baits out for the ants.  This will take care of the problem over time.

Fungus Gnats

Fungus gnats are another pest that many orchid growers find in their home and greenhouse.  The cause of this pest is love and not really understanding how orchids grow.  Many hobby orchid growers feel that watering and fertilizing is the way to go but the orchid plant has a different idea.  If you think about how and where orchids grow, you will realize that they really grow in poor conditions.  This includes very little growing medium and very little nourishment.  This is not at all what you will find in many greenhouses.  The orchids can be found planted in a lot of planting medium, overwatered, and over fertilized.   This latter environment is like a welcome mat for fungus gnats.

Prevention is the key and starts with the planting medium.  The type of planting medium that orchids require is one that breaks down quickly, which in turn reduces aeration and creates a soggy soil.  To prevent this from happening, repot your orchid often and select the ingredients of your planting medium carefully.  To extend the life of your planting medium, pick ingredients such a charcoal and coconut that is in fiber or chunk form.  Using a chunk type of medium will slow down the decomposition and settling process.

The second thing you can do is to allow the planting medium to dry out between watering and fertilize sparingly. 

The last think one can do is to simply put out a yellow sticky trap.  This will catch the flying fungus gnats and will kill them without insecticides.


Viruses do attack orchids but there is a big problem when it comes to diagnosing and treating an orchid virus.  One of the reasons why viruses are hard to treat is the fact that there are over 30 different viruses that attack orchids.  The second reason that viruses are hard to control is the fact that their symptoms are so vast.  To put this in perspective, let’s just take a look at what some of the symptoms are.  This includes yellow strips, lesions of different sizes, purple splotches, yellow to red lesions, and downward curled leaves. 

When it comes to viruses, one of the approaches is to test for viruses in a laboratory.  While these tests do look for vectors that can indicate a virus, most of the time the test if for Odontoglossum ring spot (ORSV) and Cymbidum mosaic virus (CyMV), which are the common viruses of orchids around the world.  These tests are not available to the hobby gardener but do not give up if you see some of the symptoms listed above.  There are things you can do to take care of a virus infestation even if you do not know what it is.

The first thing to do is the hardest for an orchid lover.  What is this?  Well, it is to throw away any orchid that appears to have a virus.  Once that is done, the next step is to separate out the orchids by age.  You may wonder why this is important.  The fact is that the older orchids have had more time to be exposed to viruses compared to younger plants.  Next, commit to pristine garden sanitation.   What this actually means is that you prepare to work with your orchids like a surgeon would get ready for surgery.  For an orchid gardener, what this means is to first clean your hands with soap and water.  If you really want to be careful, consider wearing gloves but if you choose this approach have a set of gloves for every orchid you may have.  You will also need to sterilize pots and tools that will be used in and around your orchids.  This sterilization is easy to do and only requires one to fill a basin with water and a capful of bleach.  Once that is done, add your pots and tools to the water and scrub.  Rinse the containers and tools in clear water and allow to dry.  After the equipment has dried, you are ready to start working with your orchids in a safe and virus free approach.


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