ARMORED SCALES. Most armored scales have several generations a year.
Armored scales overwinter primarily as first-instar nymphs and adult females.
Except for crawlers and adult males, armored scales spend their entire life feeding
at the same spot. Settled armored scales lose their legs, molt, and form their
characteristic covers, which they gradually enlarge as they grow.
Some examples of Armored Scales are: Hemlock, Juniper, Euonymus, Pine Needle, Oyster Shell and San Jose.
SOFT SCALES. Most soft scales have one generation each year and overwinter as second-instar nymphs. The multi-generational brown soft scale is an important exception Brown soft scale females and nymphs of various size can be present throughout the year. Most immature soft scales retain their barely visible legs and antennae after settling and are able to move, although slowly. At maturity, females of certain soft scales produce distinct external cottony or wax-covered egg masses.
Females of many scale species reproduce without mating (there are no males). At maturity, adult females produce eggs that are usually hidden under her body or cover. Eggs hatch into tiny crawlers (mobile first-instar nymphs), which are yellow to orangish in most species. Crawlers walk over the plant surface, are blown by wind to other plants, or can be inadvertently moved by people or birds. They settle down and begin feeding within a day or two after emergence.
Settled nymphs may spend their entire life in the same spot without moving as they mature into adults. Nymphs of other species can move slowly but rarely do, such as when species that feed on deciduous hosts move from foliage to bark in the fall before leaves drop. For species with multiple generations, all scale life stages may be present throughout the year in areas with mild winters.
When plants are heavily infested with scales, leaves may look wilted, turn yellow,
and drop prematurely. Scales sometimes curl leaves or cause deformed blemishes
or discolored halos in fruit, leaves, or twigs. Bark infested with armored
scales may crack and exude gum. Certain armored scales also feed on fruit,
but this damage is often just aesthetic. Soft scales infest leaves and twigs
but rarely feed on fruit. A major concern with soft scales is their excretion
of abundant honeydew, which contaminates fruit, leaves, and surfaces beneath plants.
Honeydew encourages the growth of black sooty mold and attracts ants, which
in turn protect scales from natural enemies.
When numerous, some scale species weaken plants and cause them to grow slowly.
Branches or other plant parts may die if they remain heavily infested with scales.
If plant parts die quickly, dead brownish leaves may remain on branches, giving
them a scorched appearance. Several years of severe infestations may kill young
plants. Certain armored scales may be more likely to kill plants. Soft scales reduce
plant vigor, but seldom kill trees or shrubs.
Scales are often well controlled by beneficial predators and parasites, except when these natural enemies are disrupted by ants, dust, or application of persistent broad-spectrum insecticides. Preserving (conserving) the populations of parasites and predators (such as by controlling pest-tending ants) may be enough to bring about gradual control of scales as natural enemies become more abundant. If scales become too numerous, a well-timed and thorough spray using horticultural (narrow-range) oil applied either during the dormant season or soon after scale crawlers are active in late winter to early summer should provide good control. Complete spray coverage of infested plants (such as the underside of leaves) is needed to obtain good control. Thorough spray coverage is especially critical when treating armored scales and oak pit scales, as these scales are generally less susceptible to pesticides than soft scales.
Inspect plants to determine whether female scales, nymphs, honeydew, or sooty mold are present. When assessing whether scales or their damage are abundant enough to prompt you to manage them, distinguish live scales from dead or parasitized ones by flipping over the female scale body or cover using a sharp tool. The dead scales from previous generations can remain on plants, and sometimes a large proportion of scales are dead or parasitized by natural enemies. During the growing season, inspect trunks for ants. If the descending ants have swollen, almost translucent abdomens, they are probably feeding on honeydew produced by scales or other insects that suck plant juices. Tracing back trail-making ants can lead you to colonies of the honeydew-producing insects.