Scale Insects
Tending to my leafy friends became a meditative activity for me during quarantine. Mark and I had just finished up lab work, and I felt the need to unwind. I made a visit over to my potted outdoor plants. My neglection caused a potted heuchera (Coral Bells) to become pest bait. As I plucked away the withered and old leaves, my attention became focused on numerous wriggling bodies crawling along the heuchera’s remains. I also noticed a trail of ants circling two distinct types pests: long-tailed mealybug and an unidentified soft-scale species.
What to Look For
Scale infestation signs:
circular flat bodies (usually females or nymph stages), winged insects under leaves (this is usually the male), crawlers (nymph stages)
Scale infestation symptoms:
honeydew drippings (indicator of soft scale), black sooty mold, poor growth, yellow regions on the surface of leaves, branch dieback, white fizzy material (indicator of whitefly or mealybug)
The video and images below were taken using a loupe held near the camera lens of an iPhone 11. Notice how the mealybug crawling eerily along the stem!
Scale Damage
Scales use their piercing-sucking mouth parts to feed on sugary plant fluids. At a high density, these pests will decrease your plant’s and tree’s health. Learning more about these pests will help you prevent pest populations from causing harm to your plants.
It is also important to note that piercing-sucking pests are capable of spreading plant disease. This is comparable to mosquitos transmitting diseases within the humans species.
Here is an abundance of whitefly found on our client’s citrus tree. The “stippling” (see pointed arrow) is caused by the feeding,
Notice the winged adult compared to the younger life stages (the small white bodies covered in white material). These are the same species of whitefly although their appearance is vastly different.
Also, check out the ants! The ants quickly became alert as I held the leaf. Their main priority was to protect their precious whitefly from me: a potential threat.
Black Sticky Stuff & Soft Scale:
In Southern California one of the most obnoxious of scales is the notorious tulip tree scale. Despite the tulip tree scales’ common name, our southern magnolia trees are hit extremely hard by tulip tree scale populations. These soft scales excrete great amounts of honeydew, causing streets, sidewalks, and cars to be covered in a sticky mess. A fungus called black sooty mold will grow on the honeydew.
When an abundance of black sooty mold covers a large quantity of surface area, photosynthetic processes may be reduced. What I find to be even more annoying than the sticky black sooty mold is the symbiotic relationship between most soft-bodied insects and ants. Insects including aphids, soft scales, and tree hoppers become “farmed” by ants. The sweet sugary honeydew produced by the leaf-sucking pests is collected by the protective ants. Ants will defend their precious farmed insects from other predacious insects.
Scale Biology
Life cycle: including; egg, crawler, several instars (number depends on species), adult. Some species also contain a pupae stage in their life cycle.
The male adults do not usually cause damage. They exist only to reproduce. Crawlers and females extract nutrients, causing damage to the plant.
Scale species are known to be sexually dimorphic (male and female appear different).
Symbiotic Relationship: Ants are an indicator of soft-bodied pests. Soft scales feed on plant tissues which eventually leads up to the disposal of plant sugars. Ants will feed on this sugary excrement also known as “honeydew”.
Scale Lineage
Order: Hemiptera* (true insects) are common plant feeders (phytophagous).
*Hemiptera species are an important order of insects affecting ornamental and agricultural crops. Majority of Hemiptera species have “piercing sucking” mouthparts. This type of mouthpart is often associated with plant feeding, meaning their main source of nutrients come from plants.
Suborder: Sternorrhyncha
Family: Diaspididae (waxy and armored scales), Coccidae (soft scales), Aleyrodidae (whitefly)
Plant Preference: There are numerous species of both scale and mealybugs. Scale and mealybug species are genetically selective when it comes to the species of plants they feed on. Some species have a wide range in diet which makes them polyphagous.
The mighty Cryptobug (Cryptolaemus montrouzieri ) feasts on pesky mealybug!
Treatment Options:
Biocontrol-Contact your local insectary. While employed at a horticultural pest control company, I regularly worked with Rincon Insectary, an operation located in Ventura, CA. Every phone call I had made resulted in great customer satisfaction. The employees are kind and willing to answer any questions relating to biocontrol.
Spray-Scales excrete a waxy substance on their backs which makes them more resistant to pesticides. Physically removing a reasonable amount of pest is a good way knock down a heavy population. After the removal it is spray time! I like using a neem oil mixture. We apply several applications about two weeks apart (depending on the pest, pest density, threshold, environment, etc.). Make sure not to spray during warm days (average of 80 degrees Fahrenheit or warmer). Spraying oils during high humidity and high temperatures days will cause damage to plants. Some plant species are more sensitive than others. Always read and follow the label!!!
Scale species are extremely diverse. Their individual life cycles must be studied thoroughly to ensure the effectiveness of our pest management programs. Some stages of the life cycle are more susceptible to being controlled than others. Knowing when to take action and when your efforts would be deemed as pointless is extremely important. You never want to apply pesticides when it’s not appropriate. Refer to university and government programs for accurate information.
Plant Pest Identification
If you happen to see anything alarming or mentioned as an important agricultural pest species, it is best to contact your county’s agricultural commissioner’s office, local university agriculture extension, or other official agencies. Most public entities will accept samples of the insect. They usually have an entomologist on staff or the sample is sent to an identification lab.
I also like using the iNaturalist app. You can download this identification app on your iPhone or Android device,
Please feel free to email us for any questions regarding treatment options. We are here to help improve our urban environment.
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