Scale insects are one of the nastier bugs that attack the ornamental plants in your garden.
Most scale insects have a waxy cover they use to camouflage their presence, allowing them to dehydrate your plants and become vast colonies before you’ve even noticed their presence.
The armored scale is one of the biggest threats your garden will face. Resistant to a variety of pesticides and difficult to spot until it’s nearly too late, these insects make common aphids look harmless by comparison.
What is Armored Scale?
One of the three largest families of scale, armored scales hail from the family Diaspididae.
Much like their soft scales (Coccidae) kin, armored scale insects produce a waxy covering called a test to shield their presence. Unlike their kin, however, this wax shield isn’t attached to their bodies and may be removed to reveal the insect beneath.
Different species of armored scale can have very different life cycles, but a few things tie them together. Once the eggs hatch, the young armored scales, known as crawlers, spread out in search of a good feeding spot.
This might be as close as a few inches away. Once they’ve found a good spot, armored scales insert their mouthparts and begin to feed.
They never move from this spot and form the armor to hide and protect them from predators and pesticides alike. They’ll generally overwinter in their test, and many species lay eggs before dying in spring.
What Damage Does Armored Scale Cause?
Armored scales harm plants by draining their fluids. A plant’s sap is its blood, and these little vampires slow the transport of nutrients as the host plants dry out.
This can cause leaf drop, disease, higher sensitivity to environmental changes, and the death of branches or even the entire plant.
While armored scale doesn’t produce honeydew (which in turn leads to black sooty mold fungus growth) like their soft scales relatives, their increased resistance to most treatment methods make them a deadly foe.
What makes scale infestations especially problematic is the way they tend to target already damaged plants.
Ornamentals along with trees and shrubs which have been affected by drought, poor planting conditions, physical damage, or sudden temperature changes tend to be compromised, encouraging infestations.
What Plants Does Armored Scale Attack?
Depending on where you live within the United States, you’re more likely to see specific types of armored scale. Many of these species are named for the host plant they most often attack, but infestation of other plants may happen when the preferred food source is unavailable.
Some of the most common armored scale species and their target plants include:
Euonymus Scale – With three to four generations per year, these attack camellias, Euonymus, hollies, and pachysandra. Only the adult female is armored and may sometimes be referred to as oystershell scale. They leave behind yellow spots on the tops of leaves and may result in excess leaf fall.
Gloomy Scale, Japanese Maple Scale – These attack the trunks and branches of red maples, as well as other trees. They have one generation per year, and their tests have a spot (offset for female, and near the edge for male). Signs include dark grey bark, branch dieback, and sparse canopies.
Juniper Scale – With circular white tests that have a yellow center, this scale species focuses on arborvitae, cypress, false cypress, and juniper. They only breed once per year, and infestations can cause needle discoloration or death.
Obscure Scale – These flat, grey pests only reproduce once per year, and their crawlers are often active for longer periods. They most commonly infest hickory and oak.
Tea Scale – Most often infesting camellia and holly leaves, this variety hatches throughout much of the year, making it harder to spot them during the crawler stage.
Infestations tend to be heavier on interior leaves, and the most common symptom is yellow spotting on infested leaves.
How To Control Armored Scale?
The easiest time to spot armored scale is when the “crawlers are active” stage. Once safely under their tent, adults are highly resistant to environmental changes, insecticides, parasitoids, and predators.
Crawler emergence and active time vary based on the species, and more than one species may be infesting your plant.
A close inspection of plants prone to scale infestation at regular intervals can help spot crawlers infestation progresses too far. Another advantage of catching armored scale during the crawler phase is the higher vulnerability they face during this time.
Try using horticultural oil, an insect growth regulator, insecticide soap, Neem oil, or a systemic insecticide. Make sure any insecticides are marked specifically for armored scale, not just for scale insects in general.
Finally, tests aren’t bulletproof. If you manage to locate soft scales or armored scale on a plant, use a good magnifier to examine infested plant surfaces to see if scales have been chewed open or there are holes in the scale covers from parasites.
In such cases, it may be better to simply monitor the situation and let the natural enemies do their job.