IPM Prescriptions for Some Common Invertebrate Pests

Copyright 1995 IPMPA

Following are general IPM prescriptions for some common insect and other invertebrate pests, including aphids, scales, spider mites, root weevils, slugs and snails, rhododendron lacebugs, tent caterpillars, fall webworms, leafminers, pearslugs, winter moths, thrips, mealybugs, whiteflies, and yellowjackets.


Aphids

Description and Biology
Aphids are small, soft-bodied insects and are most commonly light green, brown, gray, and black. Thousands of species of aphids exist and, consequently, vary considerably in color, size, response to environmental conditions, and host preference. They are typically found clustered on the undersides of leaves and on stems. The most common group of aphids lays eggs in protected places on their preferred hosts near the growing season's end, which overwinter and hatch as females in the spring. From then until near the end of the growing season, only females are present, giving live birth to more females, which already have partially formed females within them. At the end of the growing season males are produced and females are then born with eggs rather than live young inside, which are fertilized by the males during mating. Excess sap, called honeydew, is secreted as they feed and is sweet and sticky. Other insects, such as ants and honeybees, feed on the honeydew. Some ant species guard aphid colonies, killing natural aphid predators. The group known as wooly aphids is seldom a problem, and in fact rarely noticed, due to chalcid wasp predation. This is true unless populations of the parasitoid have been reduced as a result of broad spectrum pesticide use, unfavorable environmental conditions, or guarding by ants.

Target/Host
Numerous plants, especially those with tender leaves and stems which facilitates feeding. New, succulent growth is preferred.

Symptoms/Typical Damage
Aphids suck sap from soft leaf and stem tissue, causing the leaves to curl. Leaves are often able to outgrow the damage but sometimes become stunted and deformed. The honeydew often causes sooty mold to develop on infested plants. Aphids don't typically cause long term damage to trees. However, they can become a severe nuisance problem when infested trees are located over parking, picnicking, and other such areas where the honeydew falls onto vehicles, pavement, seats, etc.

Potential Natural Controls

"Forces of Nature"
Because some species alternate between two hosts during the growing season, a common situation is for large colonies to develop on a plant species and then virtually disappear as they migrate to the other host. In the case of feeding on new growth, as the leaf cuticle hardens it is more difficult for aphids to feed and they move to another host. Plant leaves are often able to outgrow damage to young leaves. Many species experience large population declines in hot weather.

Natural Predators
Aphids have many natural enemies (i.e., predators, pathogens, and parasitoids). Predators include lady beetle adults and larvae, brown and green lacewing larvae, syrphid (hover) flies, gall midges, etc. Primary parasitoids are various species of parasitic wasps. Also, during humid conditions, aphids are very susceptible to fungal diseases.

Potential Indirect Treatment Strategies

Cultural Management
Do not overfertilize plants. Aphid reproduction is accelerated when nitrogen levels are high. Avoid heavy pruning of highly susceptible plants in late winter and early spring because this encourages a flush of new growth high in nitrogen before natural controls are present. Instead, schedule pruning of these plants later in the growing season but well before fall arrives. When aging annual plants are infested but show evidence of sufficient natural enemies, either allow the plants to remain in place or cut and use as mulch underneath other plantings, especially those susceptible to aphids. When ants are observed in and around aphid colonies apply a barrier (e.g., Tanglefoot) around the trunks of woody plants and make sure other access is restricted, such as from branches touching the ground or other plants. Ant baits (e.g., Combat, Maxforce, boric acid) may also be used if necessary in the greenhouse.

Habitat Modification
Flowering plants can be introduced to provide food for parasitic wasps, which need pollen and nectar in order to reproduce. Plants that experience debilitating aphid infestations regularly should be replaced with less susceptible species.

Design and Construction
Avoid using plants that are known to be particularly susceptible to aphid infestation (e.g., lupine) as a major design component. If trees prone to aphid infestation are used, avoid placing ornamental plants underneath to prevent sooty mold problems. Such trees would best be used in a large grassy area away from other plants and paved areas, especially where cars park.

Potential Direct Treatment Strategies

Manual
Waterblasting is effective in the case of a few, localized populations. This method usually requires repeated, frequent applications (every 3 or 4 days). Small colonies can be wiped off by hand. Severely infested areas of a plant may be pruned off and dropped in a bucket of soapy water to prevent migration to other plants.

Biological
Commercially available biocontrols for aphids include the green lacewing, predatory gall midge, and lady beetle.

Introduced predators cannot be counted on to eliminate aphid populations entirely and in some cases, not even significantly because they have a tendency to devour a small percentage of a large colony and then move on to a more abundant population. However, aphid midges do not readily leave the site where they are introduced and are the most promising of the commercially available aphid biocontrols. Lady beetles have been observed to migrate quickly from the area where they were released and other problems have been experienced with their artificial release as well. Therefore, introduced lady beetles are not particularly effective. Lacewings that are released as eggs or newly hatched larvae have also shown good results. Although introduced biocontrol agents can be used effectively for aphids, it is considered preferable to rely on native predators by providing habitat for them and not using broad spectrum insecticides on a wide-scale basis. It is also important to note that small populations of aphids are actually necessary so that populations of these natural predators can be supported.

Chemical
Insecticidal soap is effective for aphid control when access is sufficient to allow for good coverage of the population. Spot treatment with a silica aerogel/pyrethrin mix, pyrethrin/rotenone mix, malathion, and diazinon is also an option. These treatments are damaging to natural predators and parasitoids and should not be used if natural controls can adequately control the population. With very severe infestations of large trees in areas where extensive honeydew cannot be tolerated, bark or injection system treatment with a systemic insecticide such as dimethoate is least disruptive to natural enemies, other beneficial insects, and the evironment in general.

Monitoring Frequency
Monitor susceptible plants often (at least once a week) while actively growing in the spring because they are more difficult to control after large numbers of leaves become curled. Observe most carefully in upwind areas and places near other infestations. Check undersides of leaves. Look for evidence of natural predators and disease-killed aphids.


Scales

Description and Biology
Scales are sucking insects and are closely related to aphids, mealybugs, and whiteflies. Newly hatched nymphs, or "crawlers", are mobile for a brief period of time but after they find a preferred location the females become sedentary and then build a protective covering where they develop into adults. The first stage nymphs are pale, flat, six-legged, and have prominent eyespots. Adult males are winged but are very weak fliers and only live long enough to mate. Although numerous species exist, those most commonly found on ornamental plants in the Pacific Northwest are the brown soft scale, oystershell scale, San Jose scale, and lecanium scale. Scales can be classified into two basic groups, soft scales and armored scales. Despite their name, soft scales have a hard shell which is generally larger and darker than armored scales. Unlike armored scales, the shell does not lift off the body when the protective covering is lifted up with a sharp knife. Armored scales are about 3 mm long and remain attached to the host plant. Soft scales typically have only one generation each year while most armored scales produce several generations.

Target/Host
Many woody plant species.

Symptoms/Typical Damage
In small numbers scales do little damage. However, severe infestations can cause yellowing of leaves, dieback of individual branches, overall decline of the plant, and even death. Soft scales can excrete significant amounts of honeydew when population levels are high. Armored scales do not produce large volumes of honeydew but can be carriers of some plant diseases and are capable of doing much greater damage to trees than soft scales. The presence of honeydew typically results in the occurrence of sooty mold.

Potential Natural Controls

Natural Predators
Populations are often sufficiently kept in check by natural enemies, most important of which are lady beetles and parasitic wasps. Parasitic wasps often reduce severe infestations to very low numbers. Evidence of parasitization is seen as holes in the outer covering where adult wasps have exited. Major scale infestations often occur after application of broad spectrum insecticides which kill natural enemies. Some ant species guard scale colonies and kill their natural enemies.

Potential Indirect Treatment Strategies

Cultural Management
Avoid overfertilization, providing only enough nitrogen to keep plants healthy, because scale populations increase significantly where nitrogen levels are high. Proper cultural management should be given to susceptible plants to ensure they are adequately healthy to withstand minor infestations and recover from damage that may occur.

Design and Construction
Avoid using plants that are known to be particularly susceptible to scale infestation as a major design component. If trees prone to scale infestation are used, avoid placing ornamental plants underneath to prevent sooty mold problems. Such trees would best be used in a large grassy area away from other plants and paved areas, especially where cars park.

Potential Direct Treatment Strategies

Manual
Severely infested branches can be pruned off if practical. Where just a few scales are present, rubbing off the adults with a gloved hand, toothbrush, or alcohol-dipped cotton swab will prevent further generations and often keep populations at sufficiently low numbers.

Biological
Releases of green lacewings, Chilocorus and Lindorus lady beetles, the Aphytis parasite, and others can help keep scale populations in check, however, biocontrols are not sufficient for initial reduction of large infestations. Where large volumes of honeydew are present on the affected plants, the beneficials can become impeded by the honeydew and it is helpful to hose it off with water if an application of insecticidal soap or oil doesn't reduce it sufficiently. Releases may be necessary once or twice a year but providing this is done, scale populations should be able to be kept below tolerance levels with biocontrols only. When ants are observed in and around scale colonies apply a barrier (e.g., Tanglefoot) around the trunks of woody plants and make sure other access is restricted, such as from branches touching the ground or other plants. Ant baits (e.g., Combat, Maxforce, boric acid) may also be used as necessary in the greenhouse.

Chemical
Insecticidal soap or superior-type oil treatments are necessary in the case of large infestations. Dormant season application of superior oils are effective against several scale species, especially San Jose and lecanium scales. If applied as a delayed dormant (i.e., just prior to budswell), overwintering mite, aphid, and caterpillar eggs can also be partially killed. If oils are used during the growing season, care should be taken to avoid injury to plants, including testing small areas of a given species before spraying the entire plant. Water stressed plants should not be treated with oil. In the case of oystershell scales, oil sprays are not effective during the dormant season because susceptible stages do not exist at this time. Oils are effective against both immature and adult oystershell scales when applied between July and September, with one application usually being adequate. Application of superior oils during the growing season should be made under moist conditions when the temperature is below 95F to avoid phytotoxicity. Insecticidal soap is only effective against immature scales and therefore timing is important. Treatments with either soap or oil can be made up to a day or two prior to release of biocontrols. Good coverage is important, especially with oils. Although organophosphate and carbamate insecticides are effective against crawlers, their use is rarely necessary for control of scale due to availability and effectiveness of the other, less toxic methods.

Monitoring
Scale populations often appear more numerous than they actually are because the shell remains for some time after the insect has died. To monitor population levels, lift a given number of scale coverings off to see how many contain a live scale. Egg masses and newly hatched crawlers still enclosed within the covering will also be present if the population is increasing.


Spider Mites

Description and Biology
This group of mites, also called webspinning spider mites, include the Pacific spider mite, twospotted spider mite, strawberry spider mite, and several other species. Species identification is not necessary because the damage caused and control measures are the same. They look like tiny moving dots to the naked eye but can be easily seen with a 10x hand lens. Adults have eight legs, an oval body, two red eyespots near the head, a large dark blotch on either side of their body (females), and are covered with long bristles. The eggs look like tiny water droplets. They live in large colonies primarily on the undersides of leaves and produce a silk webbing on infested leaves, which is a primary way to distinguish them from other mites.

Reproduce rapidly in hot weather, typically reaching their highest populations June through September. Under favorable conditions a generation can be produced in less than a week. Prefer hot, dusty conditions and are therefore often first detected in these areas. Disperse themselves to other host plants on wind currents. Can feed and reproduce year-round in warmer areas; otherwise overwinter as red or orange females underneath rough bark and ground litter. Feeding and egg-laying resumes in spring as warm weather returns.

Target/Host
Many species of woody and herbaceous ornamental plants.

Symptoms/Typical Damage
Damage is caused when the mites suck juices from the leaves; first observed as a stippling of light-colored dots on the leaves; with; with further feeding individual leaves turn yellow and drop off. Severely infested plants often have leaves and twigs covered with webbing. Water stress exacerbates damage due to more favorable conditions for spider mites and a drought-stressed, less vigorous plant.

Potential Natural Controls

"Forces of Nature"
Populations typically decline rapidly in late summer due to predation, cooler temperatures, and deterioration of host plants.

Natural Predators
Many natural predators, including predatory mites, six-spotted thrips, spider mite destroyer beetle, larvae of some "flies", and various general predators (e.g., lacewings, minute pirate bugs, bigeyed bugs).

Potential Indirect Treatment Strategies

Cultural Management
Irrigate plants to avoid water stress. Frequent overhead irrigation for longer than usual has provided effective control in some instances. This method should not be applied to plants susceptible to fungal diseases favoring moist conditions (e.g., black spot on roses) due to likelihood of infection to these plants.

Avoid applying nonselective insecticides, particularly in areas known to have spider mite problems. "Spider mites frequently become a problem after application of insecticides . . . Such outbreaks are commonly a result of the insecticide killing off natural enemies of the mites, but also occur when certain insecticides stimulate mite reproduction. For example, mites exposed to carbaryl, methyl parathion, or dimethoate in the laboratory reproduce many times faster than untreated populations. Carbaryl, some organophosphates, and some pyrethroids apparently also favor mites by increasing the level of nitrogen in leaves. Insecticides applied during hot weather usually appear to have the greatest effect on mites, causing dramatic outbreaks within a few days." (Flint)

Habitat Modification
Minimize dry, dusty conditions where susceptible plants are growing to the extent possible.

Design and Construction
Avoid use of susceptible plants, especially in hot, dusty, unirrigated areas.

Potential Direct Treatment Strategies

Manual
Water blasting of affected plants often sufficiently reduces populations. Good coverage, especially on undersides of leaves is important.

Biological
Predatory mites (e.g., Metaseiulus occidentalis, Phytoseiulus persimilis, Amblyseius californicus). For best results, a combination of species may be released. Concentrate releases in areas of most severe infestation. More than one application may be necessary. With severe infestations, treatment with insecticidal soap or a selective miticide may be necessary to bring the population to levels that can then be further reduced and kept in check with biocontrols.

Chemical
Insecticidal soap, avermectins, and neem have shown effectiveness in controlling spider mites.

Avermectins have a systemic mode of action, are applied at lower rates than conventional insecticides, have a low potential for the mites to develop resistance, and exhibit long residual activity (e.g., two applications at a seven day interval has provided 79% control for up to 35 days). (Menzies) If necessary, selective miticides (e.g., propargite) are less toxic to natural predators.


Root Weevils

Description and Biology
Adults are 6-12 mm long and dark brown or black. They are nocturnal and hide in mulch, leaf litter, ground covers, and in dark places on the stems of very dense plants during the day. During September to May the larvae are found in the soil around host plants to a depth of 2-40 cm; pupation and emergence as adults occurs from May through August; peak adult population levels occur in July. On average, only one generation is produced annually.

Target/Host
Rhododendron, viburnum, yew, hemlock, and some other broadleaf evergreens. Some rhododendrons are resistant to root weevil feeding.

Symptoms/Typical Damage
Adults make notches on leaf margins, which is the primary indicator of the presence of root weevils; however, adult feeding is difficult to detect on coniferous hosts. Adult feeding can cause extensive aesthetic damage but usually does not have a significant impact on plant health. Extensive leaf notching suggests a high population of larvae in the soil.

Larvae are legless, grublike, C-shaped, white with brown heads, and approximately 10 mm long. Larvae feed on feeder roots, root bark, and stems at or below the root crown causing girdling, wilting, decline, and even death if infestation is severe and not controlled. The most extensive larval feeding occurs just before pupation in the spring.

Potential Indirect Treatment Strategies

Cultural Management
Proper cultural management should be given to susceptible plants to ensure they are adequately healthy to withstand minor infestations and to aid in recovery from damage that may occur.

Habitat Modification
Adults need litter, ground covers, etc. in which to hide. Where feasible, keep litter cleaned up and remove ground covers altogether or at least in a one meter diameter area around bases of susceptible plants.

Design and Construction
Avoid using plants that are known to be particularly susceptible to root weevil infestation as a major design component. With rhododendrons, use species/varieties that have shown resistance to root weevil feeding.

Potential Direct Treatment Strategies

Physical
Exclusion and trapping with a sticky substance (e.g., Tanglefoot) around trunks of affected/susceptible plants will help exclude adults from the canopy and reduce leaf notching. Where practical, keep branches from touching the ground or other objects that could provide access for adult weevils. This is most practical where susceptible or infested plants are located singly or in small groups. However, it may also be feasible for particularly susceptible species/varieties within larger plantings. When in groups, place the sticky barrier around the trunks of all plants to be protected; canopies may grow together but prevent lower branches from touching the ground.

Biological
Parasitic nematodes have been effective in keeping populations at tolerable levels. Apply as a soil drench when soil temperatures and moisture are sufficient. Timing of applications is less critical than when using conventional insecticides for larval control. Applications should be made quarterly as necessary or more frequently if environmental conditions have not been conducive to nematode survival.

Chemical
Pyrethroids, rotenone, and other plant-derived insecticides are effective against adults. Spray foliage at night, beginning 3-4 weeks after adults are first detected in the spring and before eggs are laid.

If infestation is very severe, use of a broad spectrum insecticide as a soil drench may be necessary to gain initial control of larvae; spot treat. Mature larvae in the spring cause the greatest damage and are least susceptible to insecticidal control. Therefore, if insecticidal control of larvae is deemed necessary, treatments should occur before larvae mature. Neem products may also be systemically effective when applied as a soil drench.

Monitoring
Monitor for notching by adults in early May through early summer. In order to observe actual populations on a particular plant and identify adults, either place a rolled-up piece of burlap around the base of the plant and examine during the day; or use lights at night and a light colored sheet or canvas, shaking insects from foliage. Also, adults can usually be found around infested plants by digging in the surrounding soil and litter during the day. When determining treatment thresholds, remember that adults have a large egg laying capacity, and in some cases even small numbers of larvae can cause significant damage to small and/or stressed plants.


Slugs and Snails

Description and Biology
Species of slugs and snails are numerous. Introduced species are most troublesome due to lack of natural enemies and tend to be colonial whereas native species are solitary. They require moist conditions and are active at night and on cloudy days, hiding in moist, sheltered locations during the day. Snails can seal themselves inside their shells during dry conditions and can remain dormant for up to four years.

Target/Host
Primarily annual and perennial flowers and bulbs as well as ground covers. Some species are more preferred than others as food, particularly English ivy, succulents, and some bulbs.

Symptoms/Typical Damage
Serious damage can occur on seedlings, newly emerging perennials and bulbs, and in some cases, established annual and perennial flowers. Flowers can also be disfigured and flower buds either deformed or destroyed.

Potential Natural Controls

"Forces of Nature"
Rarely a problem when microclimate conditions are hot and dry, but the slugs/snails return when conditions become moist again. High populations of ground beetles and garter snakes also keep slugs and snails in check.

Potential Indirect Treatment Strategies

Cultural Management
Dense vegetation of susceptible plants can be thinned out to allow for air circulation and sunlight penetration. Thick mulches can then be placed in thinned areas to discourage weed invasion. Some types of mulches (e.g., rough cedar chips) have been observed to discourage slugs and snails.

Habitat Modification
Keep moist, shady areas to a minimum in and around flower beds. Dense foliage around the bases of plants can be removed when practical. Boards, bricks, and other such hiding places laying on top of the ground should be avoided or removed.

Design and Construction
Avoid using plants that are known to be particularly susceptible to slug and snail damage as a major design component.

Potential Direct Treatment Strategies

Manual
Hand picking can significantly reduce numbers of immature and adult slugs and snails. Hand picking is most successful at night when slugs are most active. A combination of hand picking, trapping and barriers usually provides sufficient control.

Trapping
Various trapping methods include using overturned clay flower pots (these are especially attractive to them if crushed slugs and snails are kept on the sides of the pots), inverted grapefruit halves (they are attracted to the citrus and moist, shady conditions), and beer or a mixture of water and yeast in homemade or commercial traps.

Barriers
Several materials have been used as barriers with varying degrees of success. These include copper, zinc, and salt-impregnated strips; and dry wood ashes, sawdust, and diatomaceous earth. For barriers to be effective, care must be taken to keep vegetation, soil, and other materials from forming "bridges" that allow slugs entry to the protected area. Barriers are most practical around small planted areas, particularly raised beds and containers. Excellent success has been reported with salt impregnated barriers.

Biological
Research and field trials have been conducted regarding the use of rove beetles, protozoans, decollate snails, and ducks and other animals as biocontrol agents. These are either not yet available or impractical for effective use as slug and snail biocontrol on large scale landscape plantings.

Chemical
Baits are preferred to broadcast applications of commercially available poisons for slugs and snails. Baits should be placed in areas of preferred habitat and well-hidden from children, dogs, and other pets. Use poisons only where/when other options are not feasible.


Rhododendron Lacebugs

Description and Biology
Adults are small (3-6 mm) with netlike veins in the wings which gives the insect a lacelike appearance, somewhat flattened, and dark brown or black. The insect overwinters as eggs which are laid in the midrib on undersides of leaves. Eggs usually hatch sometime in May to early June, depending on climate and yearly climatic variation. Nymphs are spiny, dark, and move with a strange sideways motion. Anywhere from one to three or more generations are produced each year, also depending on location; one generation per year is most common in the Pacific Northwest.

Target/Host
Rhododendron spp. and Kalmia latifolia.

Symptoms/Typical Damage
Top surfaces of leaves show a yellowish speckling as adults and nymphs suck sap from underneath; most prominent on rhododendrons grown in full sun. Brown and black varnishlike "tar spots" from fecal matter will be present on the undersides of leaves, which is what distinguishes the presence of lace bugs from other mites and insects that cause similarly appearing damage to the tops of leaves. It is also typical for the "skins" of molted nymphs to remain on the undersides of leaves. Affected leaves retain their yellowed appearance for a year or more and are less functional. Therefore it is preferred to treat the problem before it becomes too apparent, particularly in high profile ornamental plantings.

Potential Indirect Treatment Strategies

Cultural Management
Proper cultural management should be given to susceptible plants to ensure they are adequately healthy to withstand minor infestations and recover from any greater damage that may occur.

Design and Construction
Provide optimum growing conditions for plants; avoid planting most Rhododendron spp. in sunny areas. "High populations of lace bugs, and consequently higher degrees of damage, occur on azalea and rhododendron when they grow in sunny rather than shady locations." (Johnson and Lyon)

Potential Direct Treatment Strategies

Manual
If affecting small areas only, thumb and forefinger can be drawn along affected leaves to destroy the insects.

Chemical
Treat when necessary in late spring when young nymphs are present. Insecticidal soap has been demonstrated to be effective. In the case of contact insecticides more than one application may be necessary. If infestation is very severe a systemic insecticide such as Orthene may be necessary for initial control. Neem products may also be systemically effective when applied as a soil drench.


Tent Caterpillars

Description and Biology
Overwinter as eggs, with larvae hatching when wild cherry leaves are unfolding. Young caterpillars move to a major branch fork or crotch and build a web where they feed on newly opened leaves. After larvae mature, they leave the host tree and spin a cocoon, where they develop into reddish brown moths in early to midsummer. One generation occurs per year.

Target/Host
Maple, alder, hazelnut, hawthorn, ash, apple, cherry, currant, rose, willow, and other hardwood species. (Prefers apple and cherry.)

Symptoms/Typical Damage
Trees can be completely defoliated during very severe infestations and may be killed, but this is not common. New foliage is usually produced and long term damage is rarely serious, only aesthetic.

Potential Natural Controls

Natural Predators
A variety of natural control agents attack the immature stages. The most important parasitic wasps are Tetrastichus malacosomae and Bracon xanthonotus.

Potential Indirect Treatment Strategies

Cultural Management
Proper cultural management should be given to susceptible plants to ensure they are adequately healthy to withstand minor infestations and recover from damage that may occur.

Design and Construction
Avoid locating species known to be particularly susceptible to tent caterpillars in high profile ornamental areas.

Potential Direct Treatment Strategies

Manual
If accessible, tents and caterpillars can be easily removed with pruners and destroyed; removal should be timed during cool, rainy weather - the larvae do not leave the nest then. Egg masses may also be removed during the winter.

Biological
Bt (Bacillus thuringiensis) can be used in severe infestations. Repeat in short cycles to control new larvae as they emerge over time.

Monitoring
Monitor susceptible species in late spring and early summer. If large populations are observed, remove tents on cool, wet days to prevent even larger populations the following year.


Fall Webworms

Description and Biology
Adult moths emerge late spring to midsummer and deposit eggs in hair-covered masses on undersides of leaves. After hatching, larvae build silken webs at the ends of branches and feed within them. Disturbed larvae make jerky movements in perfect rhythm.

Target/Host
Alder, madrone, honeysuckle, apple, poplar, cherry, willow, viburnum spp. and other hardwoods.

Symptoms/Typical Damage
Primarily aesthetic; rarely serious, partly because defoliation occurs late in the summer when deciduous plants are preparing for winter dormancy.

Potential Indirect Treatment Strategies

Cultural Management
Proper cultural management should be given to susceptible plants to ensure they are adequately healthy to withstand minor infestations and recover from damage that may occur.

Design and Construction
Avoid locating species known to be particularly susceptible to fall webworms in high profile ornamental areas.

Potential Direct Treatment Strategies

Manual
Tents are easy to prune off since they are built on the ends of branches. Other control measures are rarely necessary.

Monitoring
Monitor susceptible species in late summer. If large populations are observed, remove webs and larvae to prevent even larger populations the following year.


Leafminers

Description and Biology
Numerous species whose immature and/or adult stages tunnel and feed between the upper and lower leaf surfaces are known as leafminers; each species makes a characteristic pattern of blotches or winding gallery mines. Species identification is generally not necessary for control as they are all treated similarly.

Target/Host
Various ornamental trees, including gray and paper birch (European, river, black, and yellow birches are rarely bothered), elms, alder, hawthorn.

Symptoms/Typical Damage
Heavy infestations can inhibit plant growth, but leafminers are primarily aesthetic pests on trees. Outbreaks often occur following insecticide treatments for other pests; treatment is usually not necessary where wide scale applications of broad spectrum insecticides have not occurred.

Potential Natural Controls

Natural Enemies
Parasitic wasps and natural predators (e.g., ants, true bugs, flies, lacewings, birds, spiders) usually provide adequate control.

Potential Indirect Treatment Strategies

Cultural Management
Proper cultural management should be given to susceptible plants to ensure they are adequately healthy to withstand minor infestations and recover from damage that may occur.

Design and Construction
Avoid using plants that are susceptible to leafminer damage as a major design component.

Potential Direct Treatment Strategies

Biological
A chalcid wasp (Diglyphus isaea) and a braconid (Dacnusa sibirica) are two commercially available parasitoids for greenhouse situations and may be useful in outdoor settings.

Chemical
Avermectin (e.g., Avid) is a microbially derived insecticide effective against leaf miners and has little toxicity to their parasites. Neem oil acts as a repellant to adult leafminers when applied as a foliar spray and a systemic insect growth regulator (IGR) on larvae when applied as a soil drench, remaining active within the plant tissue for three weeks. Minex (methoprene) is an IGR but is only effective within new plant growth and does not affect adults. Research has also indicated positive results for leafminer control with horticultural oils. Conventional chemical insecticides have become largely ineffective due to development of resistance as a result of overuse.


Pearslugs

Description and Biology
Larvae are yellow; 11 mm long and tadpole-shaped with widest part of body at head end; covered with slimy olive-green secretion. Adults are shiny black sawflies with shaded wings; 7 mm long; and they first appear shortly after cherries and pears are in full leaf. Two generations per year are produced with adults emerging in early spring and laying eggs in leaf tissue; eggs hatch within two weeks; immature larvae feed on upper leaf surfaces for about three weeks; mature larvae drop to the ground and pupate in soil; and a second generation in late July to early August is produced with these pupae overwintering.

Target/Host
Prunus spp. and mountain ash.

Symptoms/Typical Damage
Top surfaces of leaves are eaten, causing pinkish or brown patches. Leaves may be skeletonized with continued feeding. Entire tree appears scorched during heavy infestations. Young trees are preferred. Second generation larvae cause the greatest damage.

Potential Indirect Treatment Strategies

Design and Construction
Avoid using plants that are susceptible to pearslug damage as a major design component.

Potential Direct Treatment Strategies

Manual/Physical
Small numbers can be hand picked if accessible (small trees) and water blasting may also be effective. Ash, road dust, etc. has been applied to foliage to desiccate the pest; wash off after five days to prevent spider mite infestation.

Mechanical
Shallow cultivation (5 cm maximum) in spring when cherries and pears come into full bloom helps reduce first generation larvae and fall cultivation will minimize overwintering larval population. Cultivation after the larvae drop to the ground will also help reduce population. Local practitioners and government agents can give more detailed timing information for the local area. Practical on a limited scale where affected trees are planted in a mulched area.

Chemical
Rotenone. Insecticidal soaps may also be effective. Diazinon and Sevin should only be necessary with very severe infestations. Systemic tree injections may be more desirable than canopy sprays.

Monitoring
Monitor most carefully for population levels and damage caused by second generation in late July to early August; they do the most damage.


Winter Moth

Description and Biology
A looper; fully grown larvae are light green with dark brown heads, three yellow stripes along each side of the body, a dark mid-dorsal longitudinal line, and are about 2 cm long; they crawl in the same manner as "inch worms".

Male moths have fully developed wings; light brown-gray forewings; paler hind wings; and have a wingspan of approximately 3.2 cm. Female moths are wingless and grayish brown. Eggs are laid on tree trunks and limbs in late fall where they overwinter, hatching in late winter to early spring. Newly hatched larvae crawl to feeding locations or are carried on silken threads by wind currents. Larvae hatch in late winter and feed on buds, leaves, and flowers. Pupation occurs in June and July with adults appearing in late October. A single generation is produced each year.

Target/Host
Many trees and shrubs, including birch, flowering cherries, maple, plum, poplar.

Symptoms/Typical Damage
Larvae begin feeding in early April to late May. Defoliation may occur with severe infestations.

Potential Indirect Treatment Strategies

Cultural Management
Proper cultural management should be given to susceptible plants to ensure they are adequately healthy to withstand minor infestations and recover from damage that may occur.

Design and Construction
Avoid using plants that are susceptible to winter moth damage as a major design component.

Potential Direct Treatment Strategies

Physical
Females can be trapped as they crawl up trunks to lay eggs by placing two 15 cm wide sticky bands 30 and 60 cm above the ground in late October. Replace lower band as it gets filled with debris and moths or dries out. Remove all bands in February and burn.

Biological
Two parasites have been introduced into Canada and are providing control - Cyzenis albicans, a tachinid fly, and Agrypon flaveolatum, an ichneumonid wasp. (Davidson and Lyon) Both were released in British Columbia in the early 1980's and are now well-established. An augmentation program to increase populations of native predators on Vancouver Island has also been reported.

Chemical
Insecticidal soap, methoxychlor, or Ambush are effective in early April when apple blossom buds are in the pre-pink stage. For heavy infestations a second treatment may be necessary after apples bloom.

Monitoring
When sticky bands on tree trunks are used, monitor periodically throughout the winter to make sure they are still in place and functional. Determine if chemical treatments are necessary in the spring during vulnerable periods (see chemical strategy above).


Thrips

Description and Biology
Thrips are barely visible, 5 mm or less long, insects that cluster along veins on the undersides of leaves. Their fecal spots and plant damage are usually more apparent than the thrips themselves. Adults have two pairs of wings that are fringed and normally held over and parallel to the body. Active feeding occurs during the adult and larval stages.

Most species spend prepupal and pupal stages in the ground during a resting period. Species feed on either plants or other insects and mites. Some plant-feeding thrips are also predaceous and play a beneficial role in reducing spider mite populations.

Target/Host
Various greenhouse plants.

Symptoms/Typical Damage
Thrips scrape leaf surfaces and feed on the juices, causing white or brown scars and distorted leaves.

If infestation is heavy, entire leaves become brownish or silver and look dried rather than wilted, similar to damage from windburn. Some species produce large amounts of black, soot-like specks of fecal matter on the leaves.

Potential Indirect Treatment Strategies

Cultural Management
Vigorous, healthy plants are normally capable of outgrowing damage by thrips. Dry plants are most likely to be attacked; ensure plants have adequate water and irrigate from overhead.

Habitat Modification
Periodic flooding of greenhouse floors will drown thrips that are pupating in the ground. Maintain a diversity of vegetation outside greenhouses and don't allow these plants to dry out. This provides habitat for thrips outdoors and decreases the likelihood of migration and the development of large populations inside.

Potential Direct Treatment Strategies

Manual
Waterblasting knocks thrips off of infested plants and increases inside moisture.

Physical
Research has indicated that aluminum foil mulches placed closely around plant stems both disorients them due to the bright, reflective light and also act as a barrier to species that drop to the ground to pupate. Other materials such as plastic, roofing paper, and kraft paper can be placed underneath benches to decrease pupation also.

Biological
Commercially available biocontrols for thrips are predatory mites, lacewings, and Orius spp. It may take a few months to see evidence of control with predatory mites. Lacewings are particularly useful for controlling thrips that do not pupate in the ground. Orius spp. are reported to be quite effective.

Chemical
Insecticidal soap and horticultural oils are helpful in reducing populations before biocontrols are released and for spot treatment of "hot spots". Sulfur dust has also been effective but is phytotoxic to some plants. Western flower thrips frequently become resistant to conventional insecticides.

Monitoring
Bright blue or yellow sticky traps in the form of cards or ribbon are used to detect thrips before significant damage occurs (yellow is most reliable). Place cards on stakes in individual pots or hang ribbons vertically so the top is approximately 0.75 meters and bottom is several centimeters above the plants.


Mealy Bugs

Description and Biology
Soft, oval, and usually covered with a white or gray mealy wax. Closely related to soft scales. Overwinter as nymphs or eggs. Adult males are winged but only live a few days and are rarely seen. Suck plant juices and produce honeydew like scales and aphids. Feed in dense colonies which appear as white, sticky clusters when populations are high. Reproduction can be rapid when natural predators are not present.

Target/Host
Many ornamental tree and shrub species in addition to other greenhouse plants.

Symptoms/Typical Damage
During heavy infestations large amounts of wax and honeydew are produced and coat plants. Black sooty mold is also usually associated with the honeydew. Some plants may drop their leaves and become stunted or even die if the infestation is severe.

Potential Natural Controls

"Forces of Nature"
Populations often drop substantially during summer because mealybugs are sensitive to heat.

Natural Predators
Parasitic wasps, lady beetles, lacewings, and syrphid flies normally keep mealybug populations low outdoors, but these natural enemies are often not present at all or in insufficient numbers in greenhouse environments to do so.

Potential Indirect Treatment Strategies

Habitat Modification
A quarantine area should be established for infested plants to prevent the insects from moving to unaffected plants.

Potential Direct Treatment Strategies

Manual
Pruning of infested parts of plants is feasible if the population is small and not too many plants are affected.

Physical
Screening and sealing of cracks and holes prevents mealybugs and other pests from entering and also keeps biocontrols inside. Construct or modify plant benches or shelves with ant-proof barriers so that ants cannot protect mealybugs from biocontrol agents.

Biological
The mealybug destroyer, or "crypt", is an introduced beetle usually present naturally in warm winter areas and is also available commercially for artificial release. Both adult and larvae feed on all stages and all species of mealybugs; the larvae somewhat resemble mealybugs and should not be mistaken for them. Multiple releases may be necessary.

If the citrus mealybug, the most common mealybug on greenhouse plants, is the primary problem releases of the tiny parasitic wasp Leptomastix dactylopii can also be released along with mealybug destroyers. This parasite is specific to citrus mealybugs only.

Green lacewings will feed on mealybugs but are not preferred. If lacewings are used, it should not be in conjunction with other biocontrol agents because they will prey on them also. It is especially important to keep ant populations low because they feed on the honeydew and prevent mealybug destroyers and natural enemies from destroying the mealybugs.

Chemical
If only a few mealybugs are present, they may be rubbed off with a cotton swab soaked in rubbing alcohol. Insecticidal soap is useful to reduce large infestations prior to releasing biocontrols and for spot treatment of hot spots after biocontrols have been released. Also, a 2% horticultural oil solution in water will provide control.

Mealybugs are difficult to control completely with contact insecticides due to their waxy covering and their habit of hiding in difficult to reach places on the plants. Delayed dormant treatment timing is most effective; young nymphs don't have the protective waxy coating that protects older nymphs and adults.

Monitoring
Monitor for evidence of mealybugs and begin control measures immediately upon observing their presence. Once observed monitor the population regularly to determine effectiveness of control measures and the need for further action.


Whiteflies

Description and Biology
Whiteflies are tiny insects that suck sap from plants and are closely related to aphids, scales, and mealybugs. Warm weather causes rapid development and populations can build up very quickly then if natural enemies are not present. Breeding takes place throughout the year. Eggs are tiny, oblong, and usually laid on undersides of leaves. Crawlers (first stage nymphs) are very tiny and hard to see even with a hand lens.

After molting they lose their legs and antennae, are oval and flattened like small scale insects, and become immobile; these are called scales. They go through complete metamorphosis with a distinct pupal stage. Adults are flying insects and most species are whitish yellow with dull white wings. Clouds of the adults fly into the air when infested plants are disturbed.

Target/Host
Wide range of host plants, especially begonias, coleus, fuchsias, primulas, poinsettias, salvia, and verbena.

Symptoms/Typical Damage
Some plants are able to tolerate considerable numbers of whiteflies while others are very susceptible to damage.

Larvae excrete honeydew which may be produced in large volumes if infestations are severe; plants become covered with the sticky substance along with black sooty mold. Large populations can cause leaves to yellow, wilt, appear dried out, become stunted, and/or drop off the plant.

Potential Natural Controls

Natural Enemies
Many natural enemies keep whitefly populations in check outdoors if they have not been destroyed by broad spectrum insecticides, dust buildup, and other factors. Lacewings, bigeyed bugs, and minute pirate bugs are general predators that consume whiteflies and they also have several naturally occurring parasites. The degree of parasitization can be determined by checking for round or oval holes in empty pupal cases where the parasites have exited rather than a T-shaped hole caused by the emergence of healthy adults. The color of pupae also often indicates whether parasitization has occurred; healthy pupae are evenly white or yellow while parasitized ones are usually black or dark orange. However, some whiteflies of ornamental plants have black pupae.

Potential Direct Treatment Strategies

Physical
Sticky traps are very effective at trapping adults. However, they should be taken down when populations are low and biocontrols are used because the biocontrol agents have a tendency to be attracted to the traps when the whitefly population drops. Place the traps close to affected plants. Commercial sticky traps are available and they can also be easily made with 1/4 in. plywood, masonite, or cardboard painted bright yellow and coated with one part petroleum jelly or mineral oil and one part household detergent. It is important to keep the traps clean.

Manual
Leaves that are heavily infested with larvae and pupae can be removed and destroyed in order to help reduce populations to a level that can be controlled with biocontrols.

Mechanical
Small, hand held vacuum cleaners can be effective at removing adults off leaves and sticky traps. This must be done in early morning or other times when temperatures are cool because the whiteflies are sluggish and unable to move out of the way quickly enough. Placing the used vacuum bag in a plastic bag and freezing it overnight will kill the whiteflies inside.

Biological
Encarsia formosa is a parasitoid specific to whiteflies and has been used effectively for over 50 years. Whitefly populations should be reduced to no more than one adult per leaf prior to releasing Encarsia.

Greenhouses should be screened and other cracks and holes filled to keep the Encarsia inside. Best results are obtained when environmental conditions can be controlled to favor Encarsia over the whiteflies; optimum conditions are 27C, 70% relative humidity, and a light intensity greater than 650 footcandles. In some cases, optimum conditions for the Encarsia have been reported to conflict with optimum conditions for the plants being grown (e.g., poinsettias).

Chemical
Insecticidal soap is effective with good coverage of the plants, including the undersides of the leaves. Insecticidal soaps can be phytotoxic to some plants, especially if applied during hot temperatures; apply when temperatures are cool.

Kinoprene (Enstar) is a growth regulator that affects only whiteflies and aphids and works well in conjunction with the establishment of Encarsia formosa. A 2% solution of horticultural oil in water may also be used. Conventional insecticides are harmful to biocontrols and most are not very effective due to the ability of whiteflies to quickly develop resistance.

Monitoring
Adults are usually found near the tops of plants or the ends of branches and other lighter green foliage. The eggs are visible to the naked eye and are laid in a circle, usually on the undersides of leaves. Larvae and pupae are also found on the undersides of the older, lower leaves. The scale stage is very difficult to see because they are almost translucent unless parasitized, which causes them to turn a dark color.


Yellowjackets

Description and Biology
Yellowjackets can be distinguished from other stinging insects by their appearance, nest construction, and behavior. They have stout bodies with black and bright yellow bands around their bodies. Nests are characteristically formed and multi-layered, covered with a paper-like material, and usually located in the ground, although sometimes aerial. They are rapid fliers and social insects that live in large colonies which are defended vigorously. Any disturbance around the nest can provoke mass swarm attacks, especially late in the summer. They scavenge for meat or other foods rich in protein or sugary and are commonly found around picnic tables, garbage cans, animal carcasses, etc.

Target/Host
People in the vicinity of nests and food sources.

Symptoms/Typical Damage
Can be aggressive towards humans, especially when picnicking or near other food sources. They are most likely to sting away from the nest in late summer to early fall. Individuals are capable of inflicting multiple stings, unlike bees which can only sting once. Yellowjackets are the only aggressive species of the group including wasps, bees, yellowjackets, and hornets. These other species only sting as a defensive measure when they feel threatened.

Potential Natural Controls

Natural Predators
Skunks, raccoons, badgers, and other wildlife help keep populations down in areas where adequate habitat is available. The East Bay Regional Park District in Oakland, California has had some success in intentionally using such wildlife for yellowjacket control by dripping honey around entrance holes to nests at the end of the day to attract the wildlife.

Potential Indirect Treatment Strategies

Habitat Modification
Ensure that food waste is disposed of in garbage cans that have tight fitting and, preferably, self-closing lids. Keep outsides of garbage cans clean and empty garbage regularly. Concessions selling soft drinks may include lids and straws with the cups to minimize attracting yellowjackets and to prevent them from entering the cups and being drank, especially during August and September when yellowjackets are most numerous. Pickup garbage more frequently during this time of year. At Great Falls National Park in Virginia, populations were reduced by 96% just by using lids for soft drinks, using appropriate garbage receptacles, and picking up garbage more frequently.

Potential Direct Treatment Strategies

Physical
Several traps are commercially available. Baits that attract yellowjackets include meat scraps, pet food, and toward the end of summer, spoiled fruit, jelly, and syrups. In areas where populations are high, mass trapping can reduce numbers to levels that do not cause significant problems. A drawback to traps in public settings is the potential for children to play with or near the traps and get stung.

Manual
Locate the nest and remove or destroy. It is essential to wear protective clothing while doing this and is best performed with the help of a professional or someone else skilled in yellowjacket nest removal.

Mechanical
Vacuuming of nests is useful in wall voids and during emergencies when the nest has already been disturbed. Protective clothing must be worn and two people are needed to perform the operation; one to do the vacuuming and another to excavate the nest and look for auxiliary exit holes. Complete removal of the nest should follow. This is also best left to people who have experience in handling yellowjackets.

Biological
Experimentation is being conducted at the East Bay Regional Park District in Oakland, California in using parasitic nematodes in yellowjacket bait, which are then taken back to the nest.

Chemical
Various insecticides can be used to destroy nests if other measures such as physical removal are not chosen. These include pyrethrin/rotenone, pyrenone, resmethrin aerosols, and baits containing carbaryl or encapsulated diazinon (e.g., Knoxout).

Studies also indicate silica aerogel dust and pyrethrin (e.g., Drione, Revenge), methoprene, and avermectin are also effective for use in baits. One baiting method is to treat steel wool with an insecticidal dust and plug holes to nests. The yellowjackets from both inside and out chew on the material and die.

Monitoring
Traps may be placed in safe locations for the purpose of monitoring yellowjacket population levels and locations.


Last Modified: Monday, August 14, 1995 - 3:25:43 PM

Source: IPM Access - An Integrated Pest Management Online Service

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