Scale Insect Pests of Connecticut Trees and Ornamentals

Dr. Hugh Smith, Dr. Richard Cowles, and Rose Hiskes Department of Entomology The Connecticut Agricultural Experiment Station 123 Huntington Street, P. O. Box 1106 New Haven, CT 06504 Phone: (203) 974-8600 Fax: (203) 974-8502 Founded in 1875 Email: [email protected] Putting science to work for society Website: www.ct.gov/caes Scale Insect Pests of Connecticut Trees and Ornamentals Scale insects are among the most difficult mealybug pests of Connecticut ornamentals pests of woody ornamentals to manage. include the taxus mealybug on yew, and the There are several types of scale insect, apple mealybug and the Comstock although the most common scale pests for mealybug, both of which attack many hosts. Connecticut growers are armored scales Common scale pests of Connecticut and (Diaspididae), soft scales (Coccidae) and their hosts are presented in Table 1. mealybugs (Pseudococcidae). Armored scales tend to be smaller (2-3 mm) than soft Life cycle. Depending on the species, scale scales (5-10 mm) and often appear as though insects can overwinter as eggs, immatures, they are part of the plant, making them or adults. Females lay eggs beneath the difficult to detect. Armored scales secrete a scale covering or in a cottony mass. Some hard covering that helps protect them from scale species have one generation per year; insecticides and natural enemies, and some species have a few or several prevents them from drying out. This generations per year. First stage immatures, covering can be pried away from the scale called crawlers, emerge from eggs in spring body with the tip of a blade or an insect pin. and move to a feeding site. Crawler Common armored scale pests in Connecticut emergence usually lasts 2-4 weeks. For include elongate hemlock scale on hemlock species with multiple generations per year, and fir trees, white prunicola scale on many there are repeated emergences in the warmer hosts including almond, cherry, lilac and weather. Once scale crawlers settle to feed, privet, and euonymus scale on euonymus, they become immobile. When the crawler privet and other hosts. Soft scales produce a molts into the second stage immature, it hard layer of wax on their outermost skin begins to produce the protective scale that provides protection. Unlike armored covering. Mealybugs are distinct from most scales, this outer covering cannot easily be other types of scale insect in that they removed from soft scales. Common soft remain mobile throughout their scale pests in Connecticut include the development. Adult male scales and cottony camellia scale on holly, yew and mealybugs are delicate fly-like creatures that euonymus, Fletcher scale on arbor-vitae and live a short time and are rarely observed. yew, and tuliptree scale on linden, magnolia and other hosts. Mealybugs are covered Damage. Even low density scale and with cottony waxy filaments. Common mealybug infestations cause aesthetic damage and can make plants unmarketable. foliage by hand onto a light-colored surface Scale insects have piercing-sucking, straw- will dislodge crawlers and make them easier like mouthparts which they use to feed on to detect. Plants and crawler traps should be plant fluids. Heavy infestations can checked at least once a week. A hand lens is debilitate plants, causing yellowing of useful for observing crawlers. leaves, leaf die-back and death of the plant. Soft scales and mealybugs can produce When scouting for scales insects it is copious amounts of honeydew, a sugar-rich important to look for evidence of natural excretion which makes plants sticky and enemies. Scales have many naturally- serves as a substrate for sooty mold. In occurring enemies, including predators such extreme cases, the sooty mold interferes as ladybird beetles and lacewings, and tiny with photosynthesis and trees shed the parasitic wasps that lay eggs inside the blackened leaves. Ants are attracted to scale. Ragged remnants of scales are good honeydew, on which they feed. Certain ant evidence of predation, while neat circular species will tend and protect colonies of holes in the scale are evidence that a scales in order to make use of the honeydew. parasitoid emerged. While parasitic wasps Because ants will move scales from infested are not often observed, it is not unusual to to uninfested plants, and will protect scales see ladybird beetles and other predators from their natural enemies, the first step in associated with scale infestations. Beating managing honeydew-producing scales is to samples are useful for finding scale eliminate their associated ants. Armored predators, parasites, and even scale crawlers. scales are often associated with decline or If scouting reveals the activity of natural dieback of their hosts, which may be enemies on scales, it is advisable to delay triggered by their injection of toxic saliva the application of insecticides, and to while feeding. The beech scale causes long- continue monitoring to determine if natural term changes in the bark which leads to enemies will suppress the infestation. eventual fungal infection causing an often- Options most compatible with integrating lethal canker. biological and chemical control of scales are (1) to apply a root- or trunk-absorbed Monitoring. Incipient scale infestations can systemic insecticide to limit the insecticide be monitored by visual inspection of the exposure of the beneficials, or (2) to apply a plant. Depending on the host and the selective, insect growth regulator class of behavior of the scale species, scales can be insecticide registered for control of scales found in bark crevices, twig crotches, leaf (see below). veins or other locations on the plant. Black electrical tape can be placed around twigs or Management. Cryptolaemus montrouzieri branches near a scale infestation in order to and Lindorus lophanthae are species of track the emergence of crawlers. Wrap the ladybird beetle that are commercially tape with the sticky side facing in and available for the suppression of soft scales double back to expose the adhesive on the and mealybugs. Naturally-occurring and outer surface, then double the tape over on naturalized species of Chilocorus ladybird itself one last time to leave a small handle to beetles will attack armored and other scale permit unwrapping the trap to observe the insects. Parasitic wasps are also available trapped insects. Crawlers will appear on commercially for suppression of scales. tape as yellowish, flattened insects about the However, naturally occurring populations of size of a period on printed text. Beating parasites usually will colonize sizable scale Scale Insects, Dr. Hugh Smith, Dr. Richard Cowles, and Rose Hiskes 2 The Connecticut Agricultural Experiment Station (www.ct.gov/caes) populations without having to make adequately covered, insecticidal soap may artificial releases. Under favorable only be effective against those scales that conditions, natural enemies can help keep are less protected by a well-developed scale scale populations below economically- cover. Some armored scales are not damaging levels. Natural enemies adequately controlled with horticultural oil, purchased from commercial suppliers tend possibly because there may be an air gap to work best in enclosed environments, such between the scale cover and the live insect, as greenhouses, and when pest populations which would protect it from suffocation. are low. Natural enemies are easily decimated by many commonly used Residual broad-spectrum insecticides insecticides. Broad spectrum insecticides (carbaryl, chlorpyrifos, and malathion) are such as acephate, bifenthrin, carbaryl, generally not compatible with integrated chlorpyrifos, cyfluthrin, dimethoate and management of scale or mealybug malathion are not compatible with an populations, although they may be effective integrated approach to managing scales or on their own. The very long residual other arthropod pests. Low density scale pyrethroids, bifenthrin, lambda-cyhalothrin, infestations that are being kept in check by and cyfluthrin are of special value because natural enemies can flare out of control if one thorough spray can disrupt a season of insecticides are used inappropriately. crawler activity. Cyfluthrin is especially disruptive to IPM programs because it kills The crawler stage is most susceptible to spider mite predators while not being toxic insecticides because it lacks a well- to mites; as a result, use of this product by developed protective scale cover. itself or in a mixture with imidacloprid is Furthermore, the mobility of crawlers can likely to cause rust mite and spider mite bring them into contact with insecticide outbreaks. residues on plant surfaces. For this reason it is crucial to time insecticide applications Systemic organophosphate insecticides with crawler emergence and activity. (acephate and dimethoate) have been Dormant stage horticultural oils are used to supplanted by the neonicotinoid class of suffocate all stage of scale insect, and are insecticides (acetamiprid, clothianidin, typically applied in the late winter or early dinotefuran, imidacloprid and spring when plants are not actively growing. thiamethoxam). The organophosphates are Dormant oils may discolor some species of much more toxic to the applicator, birds, and evergreen tree, and should only be applied fish, and so the U.S. EPA has been gradually when temperatures are above 40° F (4.4° C). limiting their use. The neonicotinoids can A partial list of insecticides that can be used be subdivided into two categories, based in Connecticut

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