Update: Common Orchid Pests

orchid pests

Compared to other plants, orchids are resistant to pests. But once one orchid is infected, it can quickly spread to other plants in your collection. A bad infestation can wipe out months of careful cultivation. Watching your porcelain beauties being sapped of vitality is upsetting. But if you take precautions and act quickly, your orchids will generally recover. Here's everything you need to know on preventing and recognizing common orchid pests. 

Preventing pests

Dinkum https://commons.wikimedia.org/wiki/File:Arrangement_d%27orchidées.jpg

Prevention is better than cure when it comes to fast-multiplying orchid pests. You can take precautionary measures the moment you introduce a new orchid into your collection.

Once it arrives home, look at stems, flowers, buds, the base of the plant where it meets the soil, and roots using a magnifying glass if necessary. Don't forget to check the undersides of the leaves. Look under dried sheaths too. Orchid sheaths are the leaves that cover flowers buds - a pest delicacy.

Another crucial moment for orchid inspection is when you bring them back indoors after any period outside. You can combine pest inspection with a grooming session - remove dead leaves, flowers, and any weeds that might have sprung up in the soil. Check under the rims and at the bottom of the pots. 

Incorporate pest inspection into your regular care regime. inspect the tips of new growth and undersides of leaves and sheaths each time you water. 

Keep the area you keep your plants clean. Anything in the process of decay can incubate bacteria. Hoover up loose dirt and fallen leaves. Always sterilize any gardening tools you use.

Water during the day rather than just before night-time. This will allow excess moisture to evaporate off - damp conditions can attract pests and fungus. 

Common Orchid Pests

Aphids 

Fir0002 https://commons.wikimedia.org/w/index.php?search=aphids&title=Special:MediaSearch&go=Go&type=image

Aphids are usually green but they can also be brown, black, cream, or peach. They tend to cluster together on areas of the newest growth and flower buds. They survive by sucking plant sap, releasing saliva that is toxic to the plant. 

Aphids are particularly attracted to plants that have been overfertilized with nitrogen. Another sign of aphids is the honeydew they leave behind. This will be similar appearance to the waste of other sucking insects like scale. This honeydew may also turn black and sooty. You may find these insects on your indoor orchid collection if you have left them outside for any period. 

Aphid populations can quickly explode if left untreated. They can also spread from plant to plant easily. More worryingly, aphids can transmit the bean yellow mosaic virus which poses an even greater threat to your plants. 

An organic spray for aphids is Derris. Derris is taken from tropical plants and it is a strong, long-lasting organic pest control. It is harmless to plants but controls aphids, beetles, and caterpillars. The most common form of Derris is rotenone, made from the root of the Derris plant and cube plant. It comes in a powder that you dust over the affected areas. Make sure you wear gloves and a mask on application because it can be an irritant.

You can also spray insecticidal soap or horticultural oil. Alternatively, you can hose down your plant with a strong stream of water. 

Mealybugs

Forest & Kim Starr https://commons.wikimedia.org/wiki/File:Starr_060721-9537_Plumeria_rubra.jpg

Mealybugs show up on your plant as white pieces of fluff that cluster on stems, branches of stems, and leaves. Like the aphid they secrete a sticky honeydew substance. 

Use diluted rubbing alcohol on a cloth to wipe off the mealybugs, repeating every 5 to 7 days. Alternatively, spray weekly with insecticidal soap like carbaryl, orthene, diazinon, or malathion. 

Armored scale (diapsid boisduvalli) 

Frederick Depuydt https://commons.wikimedia.org/wiki/File:Scale_insect_on_Sarracenia_leaf.jpg

This is the most destructive orchid pest. Check under dried sheaths and leaves. Like the aphid, they suck on plant sap and poison the plant. Females look flat and yellowish-white but are covered with a thick shell. These pests are often called the oystershell scale as the color and shape of the female's shells resemble that of the mollusk. Males are football-shaped and covered in white fluff, resembling mealybugs.

Adults are not mobile like aphids, preferring to cling to their chosen spot on the plant. Once the offspring have hatched from the females, they will move around to find their forever home. This is how the infestation spreads. Eggs usually hatch in spring.

All treatment methods are most effective when applied just after the crawling young have appeared and before they have developed a protective shell. The young, mobile offspring can be identified as moving specks of dust.

You can scrape away the adults with a cotton swab dipped in rubbing alcohol (Isopropyl alcohol) diluted with three parts water. Use diluted alcohol or horticultural oil spray if you need to treat many plants at the same time. Do this every 2 to 3 days. If the infestation is severe, spray using a strong insecticide. 

Soft scale (Coccus hesperidum)

Mokkie https://commons.wikimedia.org/wiki/File:Scale_insects_on_Sansevieria_1.jpg

These creatures are similar to the armored scale but have a softer shell and are brown in color. Soft scale infestations can look very similar to mealybugs once the females hatch - they incubate their eggs in a white fluffy substance. They are found on the midribs of leaves and on stems.

Scale can also infest roots. Symptoms of root scale are harder to identify except for a general loss of vigor in your plant.

Like armored scale and aphids, the waste they produce is a sticky honeydew substance. These can turn into black sooty mold. Yellow spots on the leaves are another sign of soft scale.

This pest is less destructive than the armored scale but can multiply quicker and can be more resistant to insecticides.

Treat in the same way as you would armored scale.

Red spider mite 

Mokkie https://commons.wikimedia.org/wiki/File:Spider_mites.jpg

These tend to attack soft-leaved orchids like Cymbidium. Outbreaks are likelier when the air is dry and warm.

Symptoms of red spider mite infestation are leaves with pale patches that turn black and fall off. Silk webbing on your plant indicates a severe infestation. 

To treat your orchid, spray weekly with insecticidal soap or Isopropyl alcohol. Spray the undersides of leaves too. Continue this for several weeks to kill hatching mites. Dilute the alcohol with three parts water. 

Thrips

Maximilian Paradiz https://commons.wikimedia.org/wiki/File:Thrips,_eggs_and_nymphs._(3976052605).jpg

These tiny creatures suck sap from your plant. This causes leaves to develop brown streaks, flower drop, and distorted flowers and buds.

The adults of most species are brown or black and adults are winged. As they are so small, you will have to recognize symptoms of infestation. You might find small silver marks on flowers and leaves. They are more common in summer during long periods of dry weather. 

Thrips are soft-bodied insects making them easier to kill than armored scale. To treat, spray the plant with horticultural oil like SunSpray, isopropyl alcohol, or insecticidal soap. Alternatively, swab the treatment substance onto affected areas. You can prevent infestations by increasing humidity (which your orchids will love).

A note on insecticides 

Botanical insecticides made from plants are generally less toxic than chemical pesticides. If you use any insecticide, botanical or otherwise, wear gloves and wash hands after use to prevent skin irritation. 

One is pyrethrum, derived from the chrysanthemum. It is effective on aphids, whiteflies, mites, and thrips. A downside is that it is also toxic to beneficial bugs like ladybugs and lacewings. Be careful with storage and disposal: it is also toxic to some plants, animals, and fish.

Derris is another botanical insecticide, advised for aphids but effective on other sap-sucking pests.

Neem biodegrades easily and is extracted from the seeds of Azadirachta indica. It is effective on juvenile insects and affects the feeding of mealybugs, whiteflies, aphids, and thrips. As a bonus, it does not harm beneficial insects whilst also repelling insects.

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