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SCALES Integrated Pest Management for Home Gardeners and Landscape Professionals Scale insects can be serious pests on species of scales and their tree and trees, shrubs, and other perennials. shrub hosts are listed in Tables 1–3. The impact of infestations depends Excellent color keys for scale insects on the scale species, the plant species in California are available from the and cultivar, environmental factors, California Department of Food and and natural enemies. Populations of Agriculture; see References for titles. some scales can increase dramatically within a few months, such as when It is important to correctly distinguish honeydew-seeking ants or dusty the scale family to which your pest conditions interfere with scale natural species belongs. For example, a popular enemies. Plants are not harmed by a systemic insecticide (imidacloprid, few scales, and even high populations discussed below) controls European of certain species apparently do not elm scale and most soft scales but damage plants. Soft scales and some does not control armored scales or Figure 1. Armored scale infestation on twig. other species excrete honeydew, a sweet, cottony cushion scale. Imidacloprid sticky liquid produced by insects that can dramatically increase cottony scales feed in the fluid-conducting ingest large quantities of plant sap. cushion scale populations because it is phloem tissue of the plant and excrete Sticky honeydew and the blackish sooty very toxic to one of its natural enemies, abundant honeydew, which is sugary mold growing on honeydew can bother the vedalia beetle, Rodolia cardinalis. water that drips from their bodies. Soft people even when scale populations are This important cottony cushion scale scales include black scale, brown soft not harming plants. predator is poisoned by feeding on scale, European fruit lecanium scale, scales that have ingested the insecticide. and various Pulvinaria species. IDENTIFICATION Armored Scales. Scales are unusual looking and many Armored scales, Other Species of Scale. Species people do not at first recognize them as family Diaspididae, have a flattened, in other insect families include 1 insects. Adult female scales and most platelike cover that is less than /8 inch cottony cushion scale and sycamore immatures (nymphs) are immobile, in diameter. The actual insect body scale (the woolly sac scales, family wingless, and lack a separate head is underneath the cover. The covers Margarodidae), European elm scale or other recognizable body parts. often have a differently colored, slight (felt scales, Eriococcidae), and oak pit Immature scales and adult females protuberance (exuviae, or “nipple”). scales (Asterolecaniidae). have a characteristic round or oval Concentric rings form as each nymphal to elongate and flattened or humped stage (instar) secretes an enlargement Scale Look-Alikes. Various other appearance. Immature males are often a to its cover (Fig. 1). Armored scales organisms may be confused with scales. different color and shape than females, do not excrete honeydew. Damaging These include California laurel aphid especially in later nymphal stages species include California red scale, (Euthoracaphis umbellulariae), coconut (instars). Adult male scales are tiny, euonymus scale, oystershell scale, and mealybug (Nipaecoccus nipae), cypress delicate insects with one pair of wings. San Jose scale. bark mealybug (Ehrhornia cupressi), Adult males are rarely seen, do not feed, parasitized whitefly nymphs, and and live only a few hours. Soft Scales. Soft scales, family Coccidae, psyllids such as lemongum lerp psyllid can be smooth, cottony, or waxy and (Cryptoneossa triangula) and redgum Scales insert a tiny strawlike mouthpart are 1⁄4 inch long or less. They are lerp psyllid (Glycaspis brimblecombei). into plants and suck fluids. Scales can usually larger and more rounded and Diamond “scale” infesting palms occur on bark, fruit, or leaves. Armored convex than armored scales. Their is actually the fruiting bodies of scales and soft scales are the most surface is the actual body wall of the Sphaerodothis neowashingtoniae, an common groups (families). Common insect and cannot be removed. Soft Ascomycetes fungus! EST OTES Publication 7408 PUniversity of California N Agriculture and Natural Resources revised March 2007 March 2007 Scales LIFE CYCLE 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 second-instar virgin female gravid female female adult (underside) into tiny crawlers (mobile first-instar nymphs), which are yellow to orangish crawler white cap in most species. Crawlers walk over nipple stage the plant surface, are blown by wind to other plants, or can be inadvertently moved by people or birds. They settle first instar down and begin feeding within a day or two after emergence. second-instar third- and fourth-instar male male (underside) male adult Settled nymphs may spend their entire life in the same spot without moving as they mature into adults. Nymphs Figure 2. Life stages of a typical armored scale, the California red scale. of other species can move slowly but rarely do, such as when species scales (Margarodidae), and some that feed on deciduous hosts move scorched appearance. Several years other species produce distinct external from foliage to bark in the fall before of severe infestations may kill young cottony or wax-covered egg masses. leaves drop. For species with multiple plants. Certain armored scales may be generations, all scale life stages may more likely to kill plants. Soft scales DAMAGE be present throughout the year in reduce plant vigor, but seldom kill trees When plants are heavily infested areas with mild winters. Life cycles or shrubs. and stages for scales are illustrated in with scales, leaves may look wilted, Figures 2 and 3. turn yellow, and drop prematurely. MANAGEMENT Scales sometimes curl leaves or cause Scales are often well controlled by deformed blemishes or discolored Armored Scales. Most armored scales beneficial predators and parasites, have several generations a year. halos in fruit, leaves, or twigs. Bark except when these natural enemies are Armored scales overwinter primarily as infested with armored scales may disrupted by ants, dust, or application of first-instar nymphs and adult females. crack and exude gum. Certain armored persistent broad-spectrum insecticides. Except for crawlers and adult males, scales also feed on fruit, but this Preserving (conserving) the populations armored scales spend their entire damage is often just aesthetic. Soft of parasites and predators (such as by life feeding at the same spot. Settled scales infest leaves and twigs but rarely controlling pest-tending ants) may be armored scales lose their legs, molt, and feed on fruit. A major concern with soft enough to bring about gradual control form their characteristic covers, which scales is their excretion of abundant of scales as natural enemies become they gradually enlarge as they grow. honeydew, which contaminates fruit, more abundant. If scales become too leaves, and surfaces beneath plants. numerous, a well-timed and thorough Soft Scales. Most soft scales have one Honeydew encourages the growth spray using horticultural (narrow-range) generation each year and overwinter of black sooty mold and attracts ants, oil applied either during the dormant as second-instar nymphs. The multi- which in turn protect scales from season or soon after scale crawlers are generational brown soft scale is an natural enemies. active in late winter to early summer important exception Brown soft scale should provide good control. Complete females and nymphs of various size When numerous, some scale species spray coverage of infested plants (such can be present throughout the year. weaken plants and cause them to as the underside of leaves) is needed to Most immature soft scales retain grow slowly. Branches or other plant obtain good control. Thorough spray their barely visible legs and antennae parts may die if they remain heavily coverage is especially critical when after settling and are able to move, infested with scales. If plant parts die treating armored scales and oak pit although slowly. At maturity, females quickly, dead brownish leaves may scales, as these scales are generally less of certain soft scales, the woolly sac remain on branches, giving them a susceptible to pesticides than soft scales. ◆ 2 of 8 ◆ March 2007 Scales spring/summer Central Valley of California. This mature females pruning increases scale mortality as a crawlers result of heat exposure. eggs beneath female scale When landscaping, choose plants that are relatively pest-free and well adapted to local conditions. Consider settled replacing problem prone plants. Most first females before instars pests are highly host specific. Scales egg laying that can feed on many different plants second instars on twig usually damage only certain of these fall/winter plant species and though present, do not damage other species or cultivars in the same plant genus. Notable exceptions include California red scale Figure 3. Life cycle of a typical soft scale insect (family Coccidae). (which can severely infest and damage situations. Honeydew dropping from all Citrus species) and San Jose scale Monitoring plants can be efficiently monitored (which damages many different fruit Inspect plants to determine whether using water-sensitive paper, which and nut trees). female scales, nymphs, honeydew,