Beware of scale, a common garden pest

Scale damage on indoor moth orchids. Photo by Kit Flynn.


By Kit Flynn

I have the perfect window in my kitchen where I grow many Phalaenopsis, commonly known as moth orchids. All have been given to me by various family members and friends – and, accordingly, I treasure them.

This summer, however, I noticed honeydew on several of the leaves and upon closer inspection I realized that I was harboring a neighborhood rich in scale infection. Now “honeydew” is the term used to describe the secretions of scales and aphids. It’s shiny, sticky and is not good for the plants as it encourages the growth of the fungal sooty mold, a disease that will eventually kill the plant.

There are more than 8,000 types of scale bugs but it’s not important to determine which kind your plants are supporting. Closely related to aphids, scale bugs primarily fall into two groups: (1) armored scale that produce no honeydew; and (2) soft scale, commonly found indoors and in greenhouses, that secrete honeydew. Both have a significant protective coating that prevents many insecticides from eradicating them.

This pest is not fun to acquire. To prevent its arrival, the first step you should take is plant inspection, something that I failed to do. Before admitting a plant to your collection, go over it leaf by leaf. Scale bugs do not fly so if you find yourself battling this pest, it is probable that you unintentionally introduced it into your house.

Alas, the natural predator lady beetles that enjoyed my hospitality all winter long since have departed. Other natural predators, such as parasitic wasps, really are not welcome in my kitchen. If I opt to spray them with insecticidal soap (this will take care of the baby scale bugs known as crawlers), this cannot be done in the house, much less in the kitchen. Neem oil might smother the hard-shelled females (males have wings and flutter off, leaving the females to do the damage) but you must drench the plants in neem oil. I’m not at all sure I want neem oil around my food.

And, here’s the kicker: Female scale bugs do not need the males to produce more offspring. This means scale bugs easily procreate before dying of old age or sap inundation.

Realizing I had a problem, I quickly scrubbed every leaf to get rid of the honeydew, closely inspecting the underside looking for the hard-bodied females – water spray alone will not get rid of the honeydew. Then I went up the stems to the flowers, inspecting all the nooks and crannies offered by the orchids.

The soft-bodied crawlers will find a spot on the plant so they can start sucking its sap, a process that undermines the lifespan of that particular plant if the scale bugs remain. Once the crawler acquires the hard shell it will remain on that spot for the rest of its life, sucking to its heart’s content.

During my five-week battle with this scourge, I have washed every leaf with the Swedish dishcloth I keep for this purpose. For the hard-scale bugs, I pick them off with my fingernails, rinsing my fingers as I go. For the stems I take a Q-tip dipped in rubbing alcohol and wipe the affected area. This treatment has been required at least twice a week. If a flower is heavily infected, I snip it off.

This is an important time of the year for the orchids as they’re putting out the new leaves essential for photosynthesis; their flowers will appear in late winter and early spring. If I want to save my orchids, I shall have to get rid of the scale so this will be a continual procedure – I am intent on being the winner.

Mealybugs, a form of scale bug, with their soft bodies, are different in that they can flutter off and on the plant. They seem to be partial to phlox and are usually found at the juncture of the stem and leaf. I wipe them away with my gardening gloves or if I have a hose in hand, I will spray them. Insecticidal soap (the only chemical I use in the garden) is very effective in combating them.

Aphids, close cousins to scale bugs, are the other common pest I find in the garden. Insecticidal soap is also effective against an early aphid invasion but if the invasion becomes massive, the plant must come out. I once had an evergreen that turned from green to black due to a heavy aphid infestation and the ensuing sooty mold. The only recourse was to take the tree down so close inspection of the plants in your garden is all-important.

Inspection is the name of the game for pest prevention. If I had closely inspected each orchid as I introduced it to my kitchen window, I would have prevented this scale infestation. For scale bugs to enter the house they have to be brought in. Learn that lesson and you’re on your way to having gorgeous houseplants.

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