How to Get Rid of Scale Insects on Indoor Plants Organically

Scale insects on indoor plants present a tricky problem in many respects. They can be easily overlooked until the population builds up to a troublesome level. Once detected, repeated efforts are necessary to eradicate them. And now, horticultural experts are advising against the use of the most common ecologically-oriented home remedy: dish detergent.

Scale insects are hard to spot on indoor houseplants because they are immobile for most of their life cycle. You won't notice flying bugs or crawling caterpillars when scale infestations exist. Right after they hatch, scale are called "crawlers" and briefly have the ability to move around. But soon they attach themselves to a plant by means of their sucking mouth parts and begin to do damage, causing the plant to lose leaves and reducing its vigor. At this stage, the scale develop a hard, waxy shell like a tiny armored tank and lose the ability to move. Many experts have compared their appearance to that of a tomato seed, since they are usually brown, oval and about the same size. Here's a great picture from the University of Florida Extension, Houseplant Arthropod Pest Management website.

Scale insects will attack many types of indoor plants, but they are known to love ficus trees, umbrella trees (Schefflera), and many ivies and ferns. Instead of spotting the scale insects, you may notice their residue. They excrete a clear, sticky liquid called honeydew, which can drip onto the floor, the edge of the pot or any nearby household surface. It's especially visible on leaf surfaces. When things get really advanced, black mold will grow on the honeydew.

Wise houseplant lovers know better than to use dangerous chemical insecticides, especially indoors, and a mild dish detergent solution has long been the standard home remedy for scale, as well as many other indoor plant pests. Usually, one tablespoon mixed into a quart of water is recommended.

Dishwashing products have undergone many reformulations recently, however, with the addition of anti-bacterial agents, more powerful grease-cutting ingredients, and other additives. In the Iowa State University Extension News for December 28, 2007, Entomologist Donald Lewis advises against relying on dishwashing detergent since many plants will react with sensitivity to these added chemicals. Commercially available organic insecticidal soaps are a safe alternative.

So what should we use as a safe home made scale insect eradicator for indoor plants? Many people assume Ivory Dish Liquid is soap, not detergent, and therefore it's frequently recommended for houseplant treatment. In fact, according to the Proctor and Gamble website page, History of Ivory, Who We Are, Ivory Dish Liquid is actually a detergent. Still, it remains one of the mildest. Fels Naptha and Dr. Bronner's Pure-Castile Soap are true soaps, and can be used on plants.

Before reading the advisory against dish detergent, I used Ultra Dawn Original Scent and had no problems, but I mixed it in a lower concentration, about one teaspoon, not tablespoon, in two, not one, quarts of water. I used this to clean scale insects off a ficus tree. I was careful not to use one of the many other Dawn formulas, such as bleach alternative, power scrubbers and so on.

To cut down on mess, put the plant in a laundry tub or shower stall and spray the solution thoroughly over the entire surface and then rinse with room temperature water.

My ficus tree is more than eight feet tall and too unwieldy to take to the shower, so I needed to perform the operation in my dining room. I mixed the Dawn and water in a large plastic bowl. I covered a dining room chair with a protective plastic drop cloth and put the bowl on the chair seat. Then I tilted the plant's pot over onto its bottom edge so that the plant trunk was leaning at a 45 degree angle and the leaves could be immersed in the bowl of water. Section by section, I gently swished each group of leaves in the bowl briefly. This procedure is more easily carried out with a helper, so that one person can hold the tree trunk steady, and one can do the dunking. The Dawn solution was so diluted that I didn't need to rinse.

The ficus tree prospered and looked great for about three months, but the scale came back. I neglected to do a follow up treatment.

The University of Illinois Extension Gardener's Corner site points out in its Bugs In Houseplants page that scale also lurks under the soil of infested plants, so even though you might get rid of the visible critters, several repeat applications will be necessary.

Sources:

personal experience

University of Florida Extension, Houseplant Arthropod Pest Management:http://edis.ifas.ufl.edu/LyraEDISServlet?command=getImageDetail&image_soid=FIGURE%209&document_soid=MG004&document_version=1

Iowa State University Extension News for December 28, 2007,http://www.extension.iastate.edu/news/2007/dec/072101.htm

Proctor and Gamble website,History of Ivory, Who We Are:http://www.pg.com/company/who_we_are/ivory_history.shtml

The University of Illinois Extension Gardener's Corner, Bugs In Houseplants:http://urbanext.illinois.edu/gardenerscorner/issue_05/05_winter_03.html