Armored scales. Hemiptera: Diaspididae

Scale insects are a diverse group of mostly-sap sucking insects with at least 30 families and around 8,000 species. These insects feed on leaves or branches of many ornamental plants grown in landscapes and nurseries. They attach themselves to a plant and feed by sucking fluids through straw-like mouthparts.

Scale insects can be divided into two broad categories: armored scale and soft scale. The distinction is important because behavior and management of the two groups are different. Both groups live beneath waxy covers that protect them from predators, parasitoids and pesticides. Soft scales secrete a waxy layer over themselves that cannot be separated from their body. Soft scales also excrete sugary honeydew and may move from branches to leaves during their life cycle.

In contrast, armored scales live beneath a waxy cover that is not attached to the adult body. Thus the cover (also called a “test”) can be removed to reveal the scale insect hidden below. Armored scales typically do not move once they begin to feed and do not produce honeydew.

The most species-rich family of scale insects is Diaspididae, the armored scales, with more than 2,400 described insects. Armored scales are also some of the toughest nursery pests around, because they cause severe plant damage and their “armor” makes them difficult for growers to manage effectively. They have colonized every continent except Antarctica, and are among the most invasive insects in the world. Some of the most common armored scale species in nurseries are euonymus scale, tea scale, oystershell scale, Japanese maple scale, false oleander scale, poplar scale and juniper scale. The list will vary based on your region and the crops you grow.
 

The Guide

Follow these best practices in your nursery to control scale insects.

Which scale?
It’s important to distinguish armored scales (family Diaspididae) from scales in other families such as soft scales (family Coccidae). This is because armored scales are less vulnerable to contact insecticides than soft scales. More importantly, the systemic insecticide imidacloprid does not kill armored scales but does kill soft scales. Luckily, there are two easy ways to determine if the scales frustrating you are armored.

Flip ‘em off
Use the tip of your pocketknife to flip the test off the scale. Armored scales will remain on the branch after you have removed their tests. Soft scales cannot be separated from their test so the whole insect will flip over with the cover.

Honey do, honey don’t
Armored scales do not produce honeydew but soft scales do. Thus, if the leaves below your scale infestation are covered in sticky honeydew or sooty mold you do not have armored scales.
 

FOR MORE: http://bit.ly/NMarmscales

Life Cycle

Most species of armored scales have several generations a year and overwinter primarily as first instar nymphs and adult females. Eggs hatch into legged, mobile nymphs known as crawlers, which wander around looking for new places to feed. These crawlers attach themselves to the host plant— in the case of females, permanently. Males, upon maturity, seek out females to mate with. Crawlers are the only life stage that is mobile and it is during this brief period that they colonize plants. Except for crawlers and adult males, armored scales lack obvious appendages and spend their entire life feeding at the same spot. Reproduction may be sexual or parthenogenetic. Some species are oviparous (laying eggs), others are viviparous (giving birth to living young).
 

Favored crops

Many popular ornamentals, notably roses, hydrangeas, dogwood, rhododendron, viburnum and azalea, as well as many herbaceous perennials like dahlia, phlox and zinnia are hosts.
 

Appearance

Armored scales have a flattened, platelike cover that is less than ? inch in diameter. The covers often have a differently colored, slight protuberance, and concentric rings may form as nymphs (immatures) grow and their cover enlarges. Adult female scales and nymphs of most species are circular to oval, wingless, and lack a separate head or other easily recognizable body parts. Some change in appearance as they grow, and some species have males and females that differ in shape, size and color. Adult males are rarely seen and are tiny, white to yellow insects with one pair of wings and a pair of long antennae. Some species lack males and the females reproduce without mating.
 

Chemical control

Most contact insecticides cannot penetrate the waxy covering on scale nymphs and adults, so the crawler stage is the only life stage that these insecticides control. However, systemic products containing dinotefuran, acetamiprid or thiamethoxam will aid in armored scale control.

/ HORTICULTURAL OILS / Horticultural oils are safe to use and are especially good choices for sensitive areas, such as where people are present soon after treatment. Because of their short residual, they help to conserve beneficial insect species. If possible, time spray applications to coincide with the scale crawler stage, which is most susceptible to all insecticides.
 

Symptoms

Some armored scales damage only branches, while others infest foliage or fruits. A severe infestation of armored scales may weaken or kill a tree or shrub. Some scale species, when abundant, weaken a plant and cause it to grow slowly. Infested plants appear water stressed, leaves turn yellow and may drop prematurely, and plant parts that remain heavily infested may die. The dead brownish leaves may remain on scale-killed branches, giving plants a scorched appearance. If the scale produces honeydew, this sticky excrement, sooty mold, and the ants attracted to honeydew can annoy people even when scales are not harming the plant.