People are often used to seeing insects hop, crawl and fly around. That’s why when they see a scale insect they don’t recognize it as one.
Indian wax scale is a type of soft scale.
Photo Credit: ©2005 Buglady Consulting
Florida wax scale is found along the leaf veins of holly.
Photo Credit: ©2006 Buglady Consulting
Black sooty mold was found on these magnolia leaves.
Photo Credit: ©2002 Buglady Consulting
What does a scale look like, and what type of damage do they do?
Typically, female scales attach themselves to a branch (looking like little bumps) and don’t move for most of their life. They can basically be divided into three groups: armored scales, soft scales and mealybugs (which are covered in another article).
Armored scales make up the largest family of these types of insects, but they’re the smallest in physical size, only measuring 1-3 millimeters. Females are hidden under a scale covering not attached to the insect’s body, but to the plant. This covering is formed by the insect’s ability to secrete a waxy substance in combination with molted skins. Armored scales don’t have mouthparts, they come in a variety of colors and vary in shape from circular to teardrop. Male scales are smaller and more elongated then the female in the immature stage. Some examples are oystershell scale, tea scale, false oleander, cycad aulacaspis scale and white magnolia scale.
Female armored scales keep their eggs under their scale coverings for protection until they hatch. Called “crawlers,” these immature, freshly hatched scales are only about the size of a pinhead. (They get their name from the fact that they crawl to new growth to settle.) Once a location is selected, female crawlers attach themselves to a plant, losing their legs in the first molting. They remain sessile for rest of their lives. The immature males also feed on plants, but then they pupate into mobile adults. Some develop wings (looking similar to flies), while others just crawl.
While soft scales may not come from as large a family as armored scales, they’re larger in size. Soft scale females are elongated – measuring 2-6 millimeters – oval and sometimes flattened with a waxy covering. This covering is attached tightly to the insect’s body, not the plant. Antenna, legs and mouthparts are not visible from above, but if the insects are flipped over, these body parts can be seen with a microscope. Some examples are brown soft scale, hemispherical scale, green scale and Indian wax scale.
Soft scale females don’t have to mate to produce progeny. This enables them to build populations very quickly. Once the female has mated – or not – she layers her eggs or gives live birth, depending on the species. The crawlers then select a site to begin feeding and complete development.
Unlike armored scales, soft scales excrete large amounts of a sticky waste substance, called honeydew, while they’re feeding. This sweet, sugary liquid adheres to leaves and promotes a black mold (known commonly as sooty mold) that colonizes and grows on the leaf surface. Sooty mold eventually covers leaves and stems. It inhibits infected portions of the plant from photosynthesizing, as well as causes aesthetic damage. Ants are often present as well – they feed on the sugary honeydew waste droplets.
Whether armored or soft, scale insects are often found on the undersides of leaves or on branches. Each species of scale has specific plants they are associated with. The scale blends in well, so the actual insect may not be very apparent. When scales feed underneath the leaves, yellow spots often appear on the tops of the foliage. Over time, the plant can become more chlorotic-looking, and new plant growth can be stunted. And if you’re dealing with soft scale, another symptom is the appearance of sooty mold. (Be aware, however, that sooty mold can also be caused by whiteflies and aphids.)
How do you control scales?
Treat scales when they’re young and in the crawler stage. Horticultural oil sprays work the best for scale control, but soaps can be used, too. These types of products don’t have systemic properties, which means when spraying the product, it must come in contact with the pest. So know where your pest is. A word of warning: You can burn leaves with horticultural soaps and oils. These products need to be applied when the air temperature is cool. Make sure your plants were watered well the day before you apply your control – never spray wilted plants. Following labeled rates also reduces the risk of leaf damage. More is not better. Always follow label instructions! Also make sure beneficial insects are not present when you spray. (Insecticides can kill the good guys, too.)
Beneficial insects can help with the scale problems as well. A few of the good guys are wasps, lacewings and ladybird beetles. You can attract these beneficials to your garden by planting a variety of plants. Herbs like dill, yarrow and calendula are especially attractive to these good guys. Even just planting different kinds of plants around will make the habitat more hospitable for the beneficials. Beneficials don’t like monocultures, but pests seem to love them.
Once you treat the scale problem in your garden, you can tell if the insects are dead by the “squish test,” where you just squish the scale and see if there’s moisture present. This isn’t always foolproof, though. Since scales are covered by a waxy coating, this can help hold in moisture after the insects are dead, so they may still be juicy a month after death.
Because scales don’t often look like insects, they’re often missed. It’s important to know your host plant and know if it’s prone to scale problems. Also check your plants when you bring them home – this is how most people get insect problems in the first place.