Scale insects – techniques and organic treatments to avoid them

Mealybugs are part of the scale insect family and are among the most common parasites on our indoor plants.

They can also be found in the garden at the end of spring, during summer, or in the fall.

The damage they can do is variable, as are also the shapes they can take to hide.

They have an oval shape, and mealybugs cover themselves in a white or pinkish velvet that gives the infestation a cottony appearance.
Shown here on a beaucarnea plant, they can look slightly different depending on the plant they are infesting.

It is also possible to find brown-shelled scale insects that look like small black hulls attached to stems and/or leaves.

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What is the usual season for scale insects to appear?

Scale insects and mealybugs don’t necessarily appear in any given season, but rather emerge when a set of conditions is met. Scale insects like heat and high humidity.

  • They can appear all year round on indoor plants.
  • They are common in spring, summer and until the beginning of fall in our gardens.
  • They cannot develop in winter outdoors, but it is nonetheless recommended to clear infested areas.

What conditions help them to reproduce?

As we’ve just mentioned, scale insects love heat and humidity.

  • They particularly like closed and humid environments, and most of all high temperatures.
  • A high relative humidity indoors or regularly spraying water on leaves will accelerate their development.
  • Also, the end of spring or the beginning or fall are seasons when temperatures are fairly high and outside air is moist.

Having scale insects on a plant will often lead to other plants being contaminated as well.

What are the risks for the plant?

Scale insects and mealybugs must be dealt with immediately because an onslaught can very well kill your plant.

  • The insects feed on the plant’s sap and weaken it.
  • This hinders proper plant development and growth, and can even lead to contamination by a black fungus called sooty mold.
  • On fruit trees, especially citrus trees, scale insects and mealybugs can compromise the entire harvest and even kill a whole tree if they aren’t dealt with early enough.

How to fight scale insects?

Preventive treatment against scale insects and mealybugs

  • For inside plants, treat against scale insects from fall until the beginning of spring, 3 to 4 times in all.

Curative treatment against scale insects and mealybugs

  • As soon as mealybugs appear, destroy their protective shell with a rag dipped in beer, 90-proof alcohol or soapy water, and then treat with scale insect spray.
  • If a major invasion is ongoing, burn or remove all infected branches.

A natural and organic scale insect spray

The best recipe is to mix following ingredients into 1 quart (1 liter) of water: 1 teaspoon dishwashing soap, 1 teaspoon vegetable oil, and 1 teaspoon 90-proof alcohol.

Spray this solution once a day for 3 to 4 days.

  • There are also white oil based scale insect sprays that have proven their worth.
    You can find them in specialized stores.
  • A spray based on fermented stinging nettle tea is also very efficient in case of mealybug attacks.
    It is also possible to slow their spread with a powerful blast of water or by cleaning leaves with a rag dipped in 90-proof alcohol and rinsing afterwards with water.

Take note: it is important to treat quickly, otherwise the plant will be entirely invaded and will die.

Plants often attacked by scale insects and mealybugs

scale insects

Most indoor plants such as ficus trees or hibiscus, orchids, roses, and also citrus, lime trees or basswood, hortensias, oleander, lilac, olive trees, mulberry tree, red currants, peach trees, and also, albeit less often, apple trees.

Note that citrus are particularly vulnerable to scale insects.

An efficient and timely treatment against scale insects and mealybugs will help contain spreading to other plants in your house or garden.