SOFT SCALES

There are several kinds of soft scales from the family Coccidae that attack houseplants, but they all have a few similar characteristics that easily differentiate them from hard scales. Soft scales produce large amounts of honeydew which can lead to black sooty mold, hard scales do not produce honeydew. 

If you try to remove a scale from the plant by prying up the protective covering you will find that the covering is part of the body of soft scales while hard scales are small, soft bodied insects separate from their armored shields. Eggs hatch for a period of several weeks under the protective cover of the mother scale. After hatching the crawler stage is mobile and typically moves a short distance looking for feeding sites. After they settle in, they begin to form the armored covering and start to excrete honeydew. They continue to grow for the next two to four months.

Non pesticide options:

  • Manual removal – When there is only a small infestation soft scales are easily removed by rubbing or picking them off. Any disturbance of the scale can break its fragile mouthparts causing it to starve. Scales killed this way may appear the same as live scales

  • Insecticidal soap – kills crawler stages but is not very effective on adults

  • Horticultural oil – This is a mechanical pesticide. It kills scales by suffocating them and is active on both the crawler and adult stages. It requires direct contact and has no residual action.

    Horticultural oil and other oil-based pesticides can damage leaves. They can cause burning or other damage if applied when temperatures are high (80-85F or higher) or if the leaves are sensitive. Always test it on a couple leaves first before spraying a whole plant.

    Horticultural oil can also be mixed with many other pesticides to increase their effectiveness

Insecticides 

  • Bifenthrin – Bifenthrin – a synthetic pyrethroid with a broad range of controlled pests including termites and spiders. Pyrethroids are effective for controlling soft scales but coverage must be maintained for the entire 2-4 month lifecycle to prevent further infestations. Bifenthrin is an excellent choice because it has very long residual activity. One of my favorites, bifenthrin is effective at controlling most common pests and even suppresses spider mites. In addition to plant applications it makes a good barrier spray for around the home. It is inexpensive too, you can buy it as Bifen I/T in a 16oz bottle for about $22

  • Permethrin – another synthetic pyrethroid with a smaller range of controlled pests. It is the active ingredient in dog flea collars and human lice medicine but it is a neurotoxin to cats so if you have cats keep them away from treated areas until dry (~12 hr). It can be found at home depot or lowes under the brand name Bonide eight in a 32oz container for about $20

  • Azadirachtin – Azadirachtin is a limonoid chemical derived from neem seeds that acts as an antifeedant and insect growth regulator (IGR). It is significantly more effective as a pesticide than cold pressed neem oil. Since it is oil based it should be applied early morning or late evening to avoid burning leaves plus it is safe for pollinators once dried. It has a short-term residual effect. It is effective on both adult and crawler stages of soft scales. Azadirachtin is sold in the US under the brand name Azamax from General Hydroponics. You can find it on amazon in a 4oz bottle for about $25

  • Imidacloprid – Imidacloprid is a systemic neonicotinoid that kills everything except for spider mites and hard scale. It is the most extremely effective against soft scales but since it’s a systemic it takes some time to start working and is best used as a preventative or in conjunction with a knockdown pesticide. It is available in granular form that is applied to the soil and provides protection for 90 days. I highly recommend this for all indoor plants. See “Imidacloprid” in the mealybug section for more information