The Online Gardener's Handbook 2010
Chapter 6: Ornamental Plants
Insect Control on Ornamental Plants

Table of Contents

  1. Introduction
  2. Aphids
  3. Bark Beetles
  4. Birch Leafminers
  5. Black Vine Weevils, Taxus Weevils and Strawberry Root Weevils
  6. Borers
  7. Emerald Ash Borer
  8. Birch Dieback (Birch Borers)
  9. Caterpillar Family
  10. Leaf Beetles
  11. Learn More

Introduction

In this chapter, a description of various pests of ornamental plants will be provided along with suggested management options. These management options will not include the use of pesticides. Some biopesticides and certain reduced risk pesticides are still available to the homeowner for controlling weeds and pests in lawns and gardens. For more information, refer to Chapter 2 of this handbook and the Ministry of the Environment's website. For suggestions on managing specific weeds and pests, consult local horticulturalists, Master Gardeners or your local garden supply centre.

NOTE FOR TREE OWNERS: There is an exception under the ban that allows you to hire a licensed exterminator authorized to use commercial pesticides to maintain the health of your tree. This exception applies only to pests that threaten the tree's health. For example, the exception cannot be applied to a pest that impacts the quality of the fruit but will not kill the tree itself. To obtain this exception, licensed exterminators are required to obtain a written opinion from a professional tree care specialist that a pesticide is necessary to maintain tree health. For more information, contact the Ministry of the Environment.

Note that many trees can tolerate some damage, particularly to the foliage, without suffering lasting impacts. Pest descriptions below include suggestions for cultural controls however in many situations these may not be necessary.

Aphids

Aphids or plant lice are small soft-bodied pear-shaped insects. Colours range from green to red, brown or black. They weaken the host plant by sucking its sap, usually at the tips of shoots and on the underside of young branches. Infested leaves often become cupped and misshapen. Many species also leave a sticky deposit called honeydew on the plant, which encourages the development of black sooty mould. Most aphid species have several generations per growing season.

Many plants are susceptible to aphid infestations, especially birch, chrysanthemum, flowering cherry, crabapple, honeysuckle, Norway maple, linden, rose, spirea, snowball viburnum, willow and flowering annuals.

The honeysuckle aphid is a 2 mm long, pale green to cream coloured aphid, with a fine powdery wax covering its body. It attacks the honeysuckle plant, causing stunted growth, witches brooming, and curling of the pale green leaves. The honeysuckle aphid overwinters as eggs on the twigs, hatching in the spring at bud break.

Management Options

To control the honeysuckle aphid, prune out infested branches well below the witches broom, before the buds begin to break in the spring. You should also consider applying dormant oil at this time. If possible, replace susceptible varieties with more resistant strains. For other management options, refer to the Aphids section under Apples.

Bark Beetles

Bark beetles bore into the trunks or branches of trees and deposit their eggs. Once hatched, the larvae feed on the wood, creating vertical or horizontal tunnels eventually girdling the stem. Pupation also occurs under the bark, and the adults tunnel out to move to a new site.

Bark beetles are attracted to old trees or trees weakened by transplanting shock, mechanical injury or poor soil conditions. Pine, spruce, eastern white cedar, eastern red cedar, linden, maple, hawthorn, ornamental cherries and mountain ash are most susceptible.

Thinning and dying back of leaves and the presence of wood dust are the first signs of a problem. Closer inspection reveals small holes about 2 mm in diameter on the trunk and branches. Tunnels of the ambrosia beetle are also covered with a black fungal stain.

Management Options

Transplant trees should be placed in well-prepared soil, and established trees should be protected from abiotic injury, especially to their bark. A proper fertilization program will also improve the tree's vigour by reducing competition with surrounding turf. Remove and destroy all infested trees and shrubs.

Birch Leafminers

In mid-May and again in early July, small black sawflies emerge from the soil and lay eggs on leaves. Larvae hatch and soon enter leaf tissue where they are protected against insecticides. The injury shows as large brown blotches on leaves. Badly mined leaves turn yellow and fall in mid-summer. This problem is very common on birch trees, particularly the European white birch.

Management Options

For smaller trees, leafminers can be killed by crushing the mines. Collecting and destroying damaged or fallen leaves can help reduce insect numbers.

Black Vine Weevils, Taxus Weevils and Strawberry Root Weevils

Black vine or Taxus weevils are non-flying black snout beetles 9-13 mm long. The adult black vine weevil feeds at night, making notches on edges of needles or leaves. By day, it hides in dark places under litter or mulch. The weevil is an insidious pest because the most serious damage is done by the larvae, and occurs below the soil surface. Azalea, Euonymus, hemlock, rhododendron, yew and eastern white cedar are most susceptible to black vine weevil.

The strawberry root weevil adult is a dark brown, slightly smaller (6 mm) non-flying insect that is a more common problem on herbaceous ornamentals, eastern white cedar, spruce and juniper. The adults feed at night on leaves and needles.

The weevil grubs, about 1 cm in length, have white, legless, C-shaped bodies with brown heads. They can be found at a depth of 2-25 cm around the roots. They feed on the fibrous roots and strip the bark off the larger roots, causing the plants to grow poorly, dry out and loose colour, resulting in eventual death.

Management Options

Spread a sheet of plastic under the tree and shake the branches. Adults will fall onto the sheets and can be destroyed. Remove and destroy all fallen fruit. Burlap bags laid at the base of the tree may attract beetles looking for hiding spots. Check frequently and collect and destroy the beetles. Parasitic nematodes are commercially available and may help to suppress populations of larvae. Apply in late summer/early autumn and in mid-spring to target the larval populatons. Follow label instructions closely.

Borers

Borer larvae tunnel into wood. Over the years, they can weaken and kill a plant. Signs of infestation include holes in the wood with sawdust underneath or gummy substance on ornamental cherry, plum and peach trees. Young trees, especially those recently transplanted, are very susceptible to attack by borers. Weak or old plants are also vulnerable. For more information see the section on Borers in Chapter 1.

Management Options

Protect young or transplanted trees by wrapping strong paper or burlap around the trunk from ground level to the lowest branch. Do not use tar paper as the fumes may be injurious. Continue wrapping for at least two years after transplanting. This method is not practical for shrubs. Instead, borer-infested stems should be removed. Remove any grass sod from around the trunk, either by herbicides or mechanically, and provide a thick layer of mulch, adequate fertilizer and water to promote healthy growth. When planting a white birch, provide mulch 1 m in diameter around the base of the tree and continue to enlarge as tree grows to reduce stress. Wounds in the bark make it easier for the small borer larvae to enter. Avoid wounding with tools or lawn mowers. Scrape any wounds clean. If borers are already tunnelling in the tree, poke a flexible wire into each hole, then seal with putty or similar substance. Do this in early spring and again in fall.

Emerald Ash Borer

The Emerald ash borer (EAB) is an invasive alien borer that has received a lot of media attention due to its destructiveness. It attacks and kills all species of ash. It is native to Asia, and was first discovered in Windsor, Ontario and Detroit, Michigan in 2002, and has since spread to other parts of Ontario and the northeastern United States. In Ontario it has been reported from the Cities of Hamilton, Toronto and Welland; the Municipalities of Durham, York, Peel and Halton; the City of Sault Ste. Marie, Huron County, Chatham-Kent and Elgin, Essex, Lambton and Middlesex Counties; Norfolk County, the City of Ottawa. EAB is a quarantine pest regulated by the Canadian Food Inspection Agency. To prevent the spread of EAB, the CFIA restricts movement of ash tree materials, firewood, tree trimmings, yard waste and vehicles use to transport these materials.

Emerald Ash Borer adults are small (8-14 mm), metallic green beetles that emerge through tiny D-shaped holes in the bark from sprin to summer. The larvae bore into the tree, making serpentine tunnels just under the bark, causing dieback and tree mortality.

Management Options

Keep trees well watered and fertilized. Inspect trees regularly and report any signs and symptoms of infestation to the Canadian Food Inspection Agency at 1-800-442-2342. Never move firewood from your home to another area as you could be transporting these and other invasive species to non-infested areas of the province. Consult your local professional arborist for potential treatment options.

Birch Dieback (Birch Borers)

Birch trees under stress attract bronze birch borers, which in turn can lead to dieback fungi. This is particularly true of the European birch tree, which is relatively short-lived (15-30 years) and shallow-rooted. In home gardens, it often grows under conditions of poor soil and inadequate moisture. Once the borer enters the tree, the upper and outer branches are girdled first, causing them to die, before the main stem is affected. The elongated white larvae, which develop over two years, make long winding tunnels just under the bark, appearing as spiral ridges around the branches and trunk. Yellowed, sparse leaves are early symptoms, and the tree gradually dies from the top downward.

The adult borer is a slender, olive-bronze, 12 mm long beetle that emerges from June to August through holes in the bark and feeds on leaves.

Management Options

Cut and destroy dying branches before late May. Improving the vigour of the tree will reduce the risk of infestation. Birch roots do not compete well with lawn grasses. Water the root zone deeply several times during the growing season. Control birch leafminer to reduce stress.

Caterpillar Family

The damage caused by insects in this family is predominantly defoliation. Larvae feed on the leaves of trees and shrubs, and if the infestation is serious and repeated over several seasons, the plant will be killed.

In most cases, however, plants can withstand considerable defoliation before they are seriously harmed. The effects of early season defoliators such as spring cankerworms, for example, are often overcome by a new burst of growth in late spring. Late season defoliators such as the fall webworm also cause little damage, because most growth, food storage, and bud production has already occurred.

Canker Worms, Loopers

Fall and spring canker worms and loopers are long, thin green caterpillars that move by extending forward and pulling the hind body up in a characteristic inchworm loop. Insects are most apparent in the spring, feeding on unfolding leaves. They are sporadic, however, and may be prevalent in one year, only to disappear for several years before again becoming a problem. The females are wingless moths; they crawl up the tree in fall or spring and lay egg masses on the bark. The insects feed on a wide range of plants including apple, oak, linden and beech.

Management Options

If trees are isolated, bands of sticky material such as Tack-Trap or Stick'em can be placed around the trunk in the spring and fall to trap the moths as they crawl up the tree.

Tent Caterpillars, Webworms, Leaf Rollers

The presence of these caterpillars often goes undetected until the tell-tale webbing, tents or dropping frass appear, yet it is the defoliation that is most damaging. Birch, crabapple, flowering cherry, hawthorn, juniper, privet, and linden are common host plants but many others may also be attacked.

In the spring, the eastern tent caterpillar spins a silken tent in the branch forks of apple, hawthorn, flowering cherry and other deciduous trees and shrubs. The tent is for shelter, from which the caterpillars venture out during the day to feed. The caterpillars are black and hairy, with brown and yellow lines and blue spots along the sides, and a white stripe down the back.

The forest tent caterpillar is also hairy and black, but with blue, orange and pale yellow stripes on the sides, and white footprints along the back. It prefers ash, birch, oak, poplar and sugar maple, but also attacks a wide variety of deciduous trees and shrubs. Its tents are flat mats on the bark of trees, not in the forks of the branches, and so are less obvious than those of the eastern tent caterpillar.

Spiny elm caterpillars are black-bodied, covered with small white flecks and spines, with a row of large red spots down the back. Preferring elm and willow, they will feed on birch, maple and several other deciduous trees, becoming obvious during mid-to-late spring.

Leafrollers are caterpillars that typically tie a leaf inwardly, feeding inside in a protected rolled up chamber. In Ontario, fruit tree leafroller and red banded leafroller attack many ornamental trees, shrubs and fruit trees. They can be controlled only if insecticides are applied in early spring before the caterpillars enter the protection of the rolled leaf.

White-marked tussock moths are redheaded, black and white tufted caterpillars that feed on a wide variety of deciduous and coniferous trees and shrubs, skeletonizing leaves. The larvae have reddish-orange heads and yellow bodies tufted with distinctive hair.

Satin moths, named because of their white satin sheen, are present in July and are reportedly becoming prevalent in the greater Toronto area. The brightly coloured, orange and white spotted larvae overwinter in silken cocoon-like structures, beginning to feed after leaves have developed.

Fall webworms are hairy, pale yellow caterpillars that spin large webs over branch tips of ash, birch, box elder, crabapple, cherry, linden, poplar, oak, walnut and many others in August and September.

Juniper webworms are light brown caterpillars about 12 mm long that feed at the base of juniper needles. Needles are webbed together during early fall and again the following spring.

Pine webworms are yellowish-brown larvae with two dark stripes along the length of each side. In midsummer, larval colonies feed on needles enclosed in coarse webbed frass masses on twigs and branches.

Management Options

Removal or breaking of the tents exposes the caterpillars to predators and the elements. This is particularly effective on cold evenings. During periods of warm weather, twigs with tents should be pruned out and destroyed. Hand-pick light infestations of pine webworm. Tent caterpillars produce brown, hard, foam-like egg collars on twigs, which can be pruned out or removed in winter or early spring before the eggs hatch. Tent caterpillars are often naturally controlled by a wide variety of predators, parasites and pathogens.

Gypsy Moths

Gypsy moths are a major pest of trees and shrubs in the late spring and early summer in Ontario. The larva is a dark, hairy caterpillar with a double row of five pairs of blue and six pairs of red spots on its back. The young emerge from a buff-coloured egg-mass that was deposited the previous fall, and move or are blown to suitable host vegetation. They feed voraciously on nearly any woody plant except juniper, reaching up to 7 cm long before pupation in July. The flightless female moths lay egg masses on nearly any object. Vehicles, camping equipment and similar objects, therefore, regularly carry infestations to new regions. They consume the leaves of many trees and shrubs but prefer basswood, birch, hawthorn, oak, poplar and willow.

Management Options

Before the eggs hatch, scrape gypsy moth egg masses into a container of dish detergent, which will kill eggs. Once the young have emerged, trap them by tying a band of burlap around tree trunks, and destroy any caterpillars found within. This is only practical for a small number of trees, and you must be sure to inspect the burlap daily. Gypsy moths are often naturally controlled by various predators, parasites and pathogens.

Sawflies and Larvae

These insects feed in colonies, defoliating one branch then moving to the next. Many species exist, and they attack both coniferous and deciduous trees and shrubs.

The larvae of sawflies that attack conifers feed on needles and mine buds, or bore into the pith of young shoots. Fir, larch, spruce, pine and hemlock are most susceptible. The larvae look like caterpillars but have more than 5 pairs of prolegs and lack hooked spines.

Sawflies that attack broad-leaved trees are usually defoliators but can be leaf rollers, web formers, skeletonizers, stem borers or gall makers. Dogwood, birch, mountain ash, oak, locust, privet and rose are most commonly attacked. June is a critical period for sawfly larvae development, though their presence on privet is usually seen later.

European pine sawflies have dark-greenish bodies with longitudinal stripes and black heads and appear in late May and June.

Redheaded pine sawflies have yellow bodies with six rows of black spots and reddish heads. They feed on older leaves in July and August. Multiple generations can be present at one time and will attack all leaves.

Dogwood sawflies emerge as adults from late May through July to lay eggs on the underside of dogwood leaves. The larvae feed in colonies eating all but the mid-vein of the leaf. Larvae, initially covered with a white powder-like material, are yellow with three rows of large black spots along the length of their body.

Mountain-ash sawflies are yellow larvae with four lines of black spots along the length of the body. They appear from June to early August and feed in colonies. A second generation can appear from late August to early September. Mature larvae pupate and overwinter in the soil.

Pine false webworms are the most common web-spinning sawflies, attacking red, white, Scots' and mugho pine. Adults emerge from mid-April to mid-May laying eggs on one-year-old needles. The larvae spin loose webs at the base of needles, cutting off needles to feed and producing large webbing and frass. Large bare areas remain where larvae have fed.

Rose slugs and the spiny rose sawflies attack roses. The first resemble pear slugs, slime-covered larvae, about 1 cm long, that skeletonize leaves. The second cut slits in young shoots and insert their eggs. The shoot responds by curving toward the injured side, which turns black. The larvae that emerge during June and early July are green and yellow-orange with black dots. The mature larvae fall to the ground, burrow into the soil, and overwinter as prepupa.

Management Options

Remove individual colonies by hand and destroy whenever possible. Some of these insects have natural enemies which help keep populations in check.

Cedar Leafminers

The larvae feed inside the leaves of white cedar, causing the tips to turn brown. They also overwinter here. In June and July, the adults appear as tiny grey moths that take flight in clouds when cedars are disturbed. Damage is often conspicuous in the spring, but can be confused with other causes such as winter tip injury and salt injury. Leaves are hollowed out and if held up to the light, the caterpillars can be seen in their feeding tunnels. Cedars can withstand considerable injury from leafminers before significant damage occurs.

Management Options

Clip hedges and individual plants before June, and destroy the clippings. This reduces the insect population before adult moths emerge.

Corn Rootworm Beetles

Though corn is the principal host for this pest, the corn rootworm beetle can also cause significant damage to ornamental flowers. Many beetles fly considerable distances from cornfields to feed on ornamental flowers in gardens. They can damage the petals and stamens of chrysanthemums, roses and others.

The beetles emerge in the first week of August and are light green or yellow with black stripes, about 6 mm long. There is only one generation a year.

Management Options

Flowers intended for show competition should be bagged to keep beetles out. Cut flowers should be shaken to dislodge the beetles before they are taken indoors.

Cutworms

Cutworms are various different soft hairless caterpillars ranging in colour from light cream to bronze and black; they can be spotted or striped. The adults are variously coloured moths. They feed at night on plants with soft stems. Some kinds feed below ground; others feed above, cutting the stem or eating leaves.

Management Options

Protect bedding plants by placing partially sunken cylinders made from tar paper or empty tin cans around each plant. When chewed-off plants are found, scratch the soil to find and remove the worm to avoid losing other plants. Cutworm adults are attracted to weeds to lay eggs, so good weed control can help reduce cutworm populations. Cultivation will also expose cutworms to predators. Cutworms are likely to be a problem in new gardens. Thoroughly cultivate new gardens prior to planting.

Earwigs

Earwigs are reddish-brown and about 2 cm long with a pair of forceps-like appendages at the hind end. They are active at night and hide by day in the soil or under stones or debris. They feed on many flowers.

Management Options

Place damp burlap or boards on the soil as hiding places to attract the earwigs. Remove in the morning and destroy earwigs.

Gall Forming Insects and Mites

Galls are abnormal growths that plant tissue develops in response to insect feeding, saliva, or egg-laying. They are rarely harmful, and should be seen as biological curiosities. Some of the most common are the reddish, felt-like patches that appear on maple leaves, the pouch-like galls on the honeylocust or the galls that form on various species of spruce. Damage might be unsightly, but rarely harms the tree.

Gall makers attack oaks wherever they are planted, forming galls of various shapes, sizes and colours on leaves, twigs, flowers and acorns. Oak apple galls, located on the petiole of red oak leaves, are one of the most common gall makers and cause no damage to the tree. Twig galls, however, can cause serious damage.

Maple bladder gall and spindle gall mites cause small bladder and spindle-shaped swellings on maple leaves. Another mite causes felt-like, reddish patches on leaves. These mites overwinter on the bark and buds of host trees, emerging to feed in spring as buds break. As they feed on newly expanding leaves, the plant responds by producing these galls, in which the mites live and multiply throughout the growing season.

Eastern spruce gall adelgids cause pineapple-shaped galls to form at the base of new shoots on Norway, white and occasionally blue spruce. Eggs are laid in early spring at the base of the buds. Upon hatching, the nymphs crawl to developing needles and begin feeding. Their continued feeding causes abnormal cell growth to form a series of bulb-like hollows forming the gall. Shoots are weakened and growth reduced. The galls are initially green, but turn brown later in the season. When the galls open in late July, winged immature females emerge and mature in early spring to lay eggs on the terminal needles in a mass of white cottony wax just as the new buds begin to break.

Cooley spruce gall adelgids attack mainly Colorado Blue and Engelmann spruce. They usually alternate between spruce and Douglas fir but may complete their life cycle on either host. The immature females overwinter near twig terminals. These mature in early spring and deposit eggs under masses of cottony wax. The nymphs move to the base of developing needles near the tip of new shoots and begin feeding, stimulating the formation of cone-like galls which develop rapidly and envelop the nymphs. The galls are blue to purplish and mature to brown by early June.

Management Options

In most cases, no control is recommended beyond removing the galls and destroying them.

Grasshoppers

When a lush garden is located near weedy areas, abandoned fields or woodlots, grasshoppers are often a problem. This is particularly true during dry seasons, when normal food plants are less attractive and the grasshoppers migrate into the garden.

Management Options

Trap grasshoppers in jars partially filled with molasses.

Iris Borers

The larvae of these borers feed inside iris leaves, leaving visible tunnels and watersoaked areas. They tunnel downward to the rhizomes (underground stems) and destroy the inner tissue. Infestation is often accompanied by bacterial soft rot.

Management Options

To reduce overwintering insects, gather and destroy all old iris leaves in the fall. Divide old plants soon after flowering, and remove and destroy all infested parts of rhizomes.

Lacebugs

These small bugs have scalloped, ornamental bodies that resemble lace. They feed on asters, chrysanthemums, ash, oak and other host plants, causing bleached flecking of the leaves. Lacebug infestations are also evident by small dark spots of excrement on the leaves.

Management Options

If populations are not too high, crush leaves between fingers to kill lacebugs.

Leaf Beetles

Elm and Willow Leaf Beetles

These small dark brown adult leaf beetles chew holes in leaves. The black larvae are even more damaging, as they skeletonize leaves. Elm leaf beetle attacks American and Chinese elm, while the willow leaf beetle attacks Lombardy poplar and willow.

Management Options

Hand pick and destroy adults.

Lily Leaf Beetles

The lily leaf beetle is an invasive pest first found in Montreal in 1945. It has since been reported throughout Ontario, feeding on lily, lily of the valley, Solomon's seal and fritillary. The adult beetle is distinctively shiny and red, with dark head, antennae, legs and underside. The adults overwinter in soil and plant debris, laying their eggs underneath leaves in early spring. The young larvae feed on leaf undersides while the older larvae can be seen feeding on the upper portion of the leaf.

Management Options

Hand pick and destroy adults and larvae. Inspect undersides of leaves for eggs and crush. Inspect transplants for signs of beetle before planting.

Viburnum Leaf Beetles

Viburnum leaf beetles, commonly found in Southern Ontario, attack American cranberry bush, arrow wood viburnum, European cranberry bush, mapleleaf viburnum, and nannyberry. Both larvae and adults devour the leaves, leaving only the major veins. The females deposit eggs in holes in the bark of twigs, and these are covered with a black cap of excrement in mid-summer. This provides protection but makes their presence detectable if the branches and twigs are carefully examined before leaves emerge in the spring. Eggs hatch in May and larvae begin feeding gregariously when leaves are about half expanded, completing their development in 8-10 weeks. The larvae pupate, fall to the ground, and emerge as adults in mid-to-late July.

Management Options

Twigs where eggs have been laid can be pruned out in fall or early spring.

Leafcutter Bees

The work of leafcutter bees is usually little more than a curiosity or nuisance. The small black female cuts holes in the leaves of rose, azalea, Euonymus, crabapple and other plants to line her egg cells. The bee is solitary, nesting in hollow twigs.

Management Options

Not usually required.

Leafhoppers

Both adults and nymphal leafhoppers can transmit virus diseases to host plants while feeding. Many annual and perennial plants are affected, especially delphinium, hollyhock, honeylocust, lupine, marigold, roses and zinnia. For more information, see the leafhopper section of Chapter 1.

Management Options

Wash nymphs (the more sedentary stages) off plants (especially leaf undersides) with a strong jet of water. Setting out yellow sticky traps near infested plants may trap some incoming adults, although it will also attract and trap beneficial insects (e.g. predators). Leafhoppers have a number of natural predators and parasites which can help keep populations in check.

Leafminers

The larvae of many flies, beetles, moths, and sawflies feed by tunnelling between outer leaf surfaces. Some create blotch-shaped or serpentine tunnels that can, if severe and repeated, reduce the aesthetic value and life of trees, shrubs, and herbaceous plants. Leafminers are common on birch, basswood, white cedar, crabapple, columbine, lilac, elm, oak, black locust, mock orange, spruce, and other ornamentals.

Leafminer populations vary from year to year, and may not be significant enough to warrant control.

Management Options

Follow proper sanitation procedures. Remove and destroy all prematurely fallen leaves and any leaves where symptoms are evident.

Millipedes

These animals are dark brown worms about 3 cm long with 100 or more legs. They are usually found curled up like a coil spring. They feed on manure and decaying organic matter and do little or no harm to ornamental plants; hence they should not be controlled. The millipede is often mistaken for wireworm larvae, which are cylindrical, reddish-orange insects with six pairs of legs and a hard outer skin. These larvae cause severe damage to roots of plants.

Management Options

None required.

Mites

Mites are small and spider-like, living mostly on the underside of leaves, where they suck plant sap. When numerous, the leaves turn a dull bronze colour, later becoming yellowish. Several different mite species attack ornamentals. Hot dry weather is favourable for two-spotted mite and European red mite. These mites attack crabapple, buddleia, mountain ash, rose, potentilla, viburnum, spirea, spruce, white cedar, and many herbaceous flowers. Spruce spider mite attacks juniper, spruce and white cedar and is considered a cool season mite.

Pearleaf blister mites cause serious injury and frequently brown and curl nearly all the leaves on infested trees and shrubs including cotoneaster, serviceberry, hawthorn, pear and mountain ash. Blister mites overwinter under bud scales and migrate to the young leaves to feed and lay eggs. Heavy feeding results in large patches of damaged tissue which become distorted or crinkled, brown or black and dry out.

Management Options

Mite populations can be reduced considerably by a forceful stream of water from the garden hose, directed at the underside of leaves. Repeat every several days if mites are numerous. Water stressed plants will be less tolerant of damage, so ensure irrigation is adequate. Mites have numerous natural enemies which help to keep populations in check. Predatory mites are also available for purchase and may help to provide some control.

Pear Slugs

Pear slugs are the larva of sawflies and are not true slugs. They are slime-covered, about 1 cm long, and are first dark green, later turning to orange. They skeletonize the leaves of hawthorn and cotoneaster, Amelanchier, rose, ornamental flowering cherry and plum.

Management Options

Dusting with talc or fine, dry soil helps control this insect by causing it to dry out. It may also be possible to dislodge them using a strong jet of water.

Pine Shoot Moths

Damage to pine trees is done by the larvae of these moths. They overwinter at the base of the terminal whorl of buds, and feed inside the buds in May or early June. The larvae have a light brown body and black head. The adult is a small moth with rusty orange forewings marked with irregular bands of silver. It emerges in early June to begin laying eggs near the tips of the current year's shoots. Austrian, mugho, red and Scots pines are susceptible.

A flow of resin from the bud indicates the presence of larvae. Young shoots developing at this time take on a hook-shaped appearance or are killed. The death of the shoots stimulates the development of latent buds below the point of injury, producing a witches broom.

Management Options

Whenever possible, remove infested shoots by hand in late May and early June and destroy them. Young trees less than 20 m are the most susceptible.

Pine Pitch Mass Borers

Pine pitch mass borers are the white and pink larvae of several clear-winged moths with yellow and black bodies. The larvae have a 2-3 year life cycle and affect established pines. Large pitch resin masses appear on the trunks. Stressed and wounded plants are most susceptible.

Management Options

The larvae and pupae are found under the pitch masses in May and June. They can be picked off and killed. Maintain good tree health to reduce susceptibility.

Plant Bugs

Weedy areas nearby provide food and shelter for plant bugs that migrate into the garden. Plant bugs cause shoots and flowers to become distorted, or leave round bleached spots on the leaves where they feed for sap. A large variety of ornamentals and herbs are affected, including ash, chrysanthemum, honey locust, marigold, zinnia, daisies, and mint.

Adult tarnished plant bugs (TPB) are brown, while the four-lined plant bugs (FLPB) are greenish-yellow with four black stripes. Both are triangular in front, 6-7 mm long and about half as wide. They are very active, readily flying when disturbed. Young TPB are light green, while young FLPB are bright red, each with dark spots and markings. TPB can be a problem throughout the season, while FLPB is prevalent in late spring and summer.

Management Options

Thorough cleaning of the garden in the fall is important as plant bugs overwinter as nymphs or adults in garden trash and weeds. Removing weeds and mowing grass and weeds around gardens may help reduce breeding sites. Some producers have reported success using Shasta daisies, planted in a border around their fields, as a trap crop. This only works if the daisies are kept flowering, as the bugs move out of the daisies once flowering stops. Plant bugs have a number of natural enemies. Planting nectar-producing plants around vulnerable garden plants can help to increase biological control of plant bugs.

Rose Chafer Beetles and Japanese Beetles

Rose chafers are elongated, fawn-coloured beetles, 1.5 cm long. Japanese beetles are oval-shaped with metallic green bodies and copper-coloured wings.

Rose chafer beetles emerge from the soil in large numbers during late May while Japanese beetles emerge in early July, feeding on the blooms and leaves of trees and flowers. The beetles eat the tissue between the veins, leaving a lace-like skeleton. The larvae cause considerable damage feeding on roots. Rose and peony blooms are prime targets for the rose chafer beetle, but hollyhock, zinnia, and other flowers are also attacked. The Japanese beetle feeds on the leaves of many shade trees including linden and birch, shrubs, garden flowers, wild grape, roses and raspberries during July and August. They are best seen at dusk, when they fly to the ground to lay eggs from nearby trees.

Management Options

If only a few plants are involved, shake or hand pick the chafers or beetles from the blooms into a container or sheet and destroy them. in a bucket of soapy water. If possible, locate susceptible plants away from vinyards or turf or control grubs in lawns. This will help reduce populations in your yard, but will not prevent adults from flying in from other areas. Japanese beetle traps are available in garden centers. Although the lures sold with the traps are very effective and can attract many beetles each day, research has shown that the traps attract more beetles than are caught. As a result, susceptible plants in the vicinity of the trap are likely to suffer more damage than if no traps were used. Parasitic nematodes are commercially available and may help to reduce populations.

Scale Insects

These small insects spend most of their lives under protective caps or scales attached to the bark of branches and trunks, and to pine and juniper needles. The insects suck the sap, weakening the plant. If severely infested, the bark is covered with a crusty layer of scales. One or two generations can occur per season depending on the species.

Cottony maple scales have a cottony, popcorn-like appearance and occur principally on honeylocust and maple but also ash, beech and sycamore.

Euonymus scales not only infects Euonymus but pachysandra and English ivy as well. The males are small white scales, while the females are larger and light brown in colour. Second generation nymphs are often present in late August and early September and can still be controlled.

Fletcher scales appear as large, dark brown knobs mainly on yew but also on cedar and juniper.

Golden oak or oakpit scales are small golden discs on - or slightly sunken into - the bark of oak, especially English oak.

Juniper scales consist of small white, circular specks with yellow centres on twigs and needles of juniper.

Lecanium scales look like round, brown knobs on ash, cedar, crabapple, elm, honeylocust, maple and oak.

Magnolia scales are one of the largest scales in North America. Its primary hosts are Magnolia acuminata (cucumber tree), M. soulangiana (saucer), and M. stellata (star). The mature female is about 12.5 mm long, oval convex, smooth, dark brown and covered with a waxy bloom. It overwinters as a nymph on one and two-year-old shoots and the crawlers emerge in late August and September. There is only one generation per year. Honeydew and sooty mould on the branches and leaves indicate presence of magnolia scale.

Oystershell scales, which resemble small oyster shells, infest ash, beech, cotoneaster, dogwood, lilac, linden, maple, willow and other smooth-barked plants.

Pine needle scales appear as white specks on the needles of pine and spruce, and occasionally hemlock, fir, and yew.

Pine tortoise scales are brown, oval convex scales about 6 mm long infesting several pine species.

Management Options

A light infestation may be kept in check by birds and beneficial insects. Scale biological controls are commercially available, and may help to reduce populations.

Slugs and Snails

Slugs and snails hide by day in dark, moist places and feed by night. Glistening slime trails are often left as evidence of their presence. The use of mulch aggravates the slug or snail problem.

Management Options

Earwigs are reported to keep slugs and snails under control as they eat the eggs and young slugs. Remove materials from the garden which provide daytime hiding sites such as plant debris, rocks, boards and logs. Thin or space densely growing plants. Place shallow dishes of beer or juice as bait in garden; replace frequently. Set out traps of 15 cm square boards and hand pick slugs and snails from under the boards in the morning. Barriers have also been used to keep snails and slugs out of gardens. These include copper screens buried partially in the soil or wide barriers of dry ashes surrounding the garden area. These barriers need to be checked after rain to determine whether they are still intact.

Sowbugs or Pillbugs

These pests have flat, oval, grey-brown bodies about 1 cm long, and seven pairs of legs. They live in damp areas under flowerpots, boards, etc., or in manure and decaying leaves. They seldom cause damage to ornamental leaves and flowers, and are most often beneficial by breaking down organic matter. For this reason, control is rarely recommended.

Management Options

None required.

Spittlebugs

Spittlebugs are sap-sucking insects. In their immature stages, they cover themselves with a frothy saliva-like protective mass. The adults are brown and inconspicuous, and they jump easily when disturbed. Stunting and distorting of new growth are the most common signs of damage. They are present in May and early June with usually one generation per season.

Management Options

Pick off and destroy. Spittlebugs can be washed off plants with a strong jet of water.

Spruce Budworms

Spruce budworm larvae are brown with a lateral yellowish stripe and light spots on the back. These 2.5 cm caterpillars form a small nest of silk in May or early June while they feed on the needles of spruce and fir. The adults appear in July and early August as dull grey moths, the females laying eggs on needles near the periphery of the crown or terminal growth at the top of tree and the end of branches. This insect is rarely a problem in the home garden.

Management Options

Not usually required.

Thrips

Thrips are narrow, 3 mm long insects that hide within the plant and so are seldom seen. They suck plant sap, leaving silvery speckled or streaked marks on leaves and flowers. Both adults and larvae move very quickly when disturbed, hiding deep inside growing shoots or partially opened blooms. Damage is usually serious on gladiolus, but may also occur on iris, day lily, dahlia, rose and flowering annuals. Several species of thrips can be found in Ontario gardens but their appearance and damage are similar.

Management Options

Remove and destroy flowers with thrips present. Damage may be less severe when bulbs are planted early.

Whiteflies

These small white insects are sap suckers, causing leaves to wither. In addition, the production of sticky honeydew by the feeding nymphs usually leads to the growth of sooty mould.

Whiteflies multiply quickly, which makes control difficult. Swarms of whiteflies are noticeable when plants are disturbed, and young nymphs may be found in large numbers on the underside of leaves. Coleus, fuchsia, hibiscus, hollyhock, impatiens, Jerusalem cherry and poinsettia are particularly susceptible.

Management Options

Whiteflies can become a serious problem with indoor plants. For this reason, you should be particularly careful when bringing potted plants indoors for the winter. Examine each plant carefully, prune severely to remove infested leaves; then dip the plant - though not the soil or roots - in a solution of insecticidal soap. Yellow sticky traps, available at garden suppliers, can be used inside to attract and capture adults.

White Grubs and Wireworms

These are the larvae of June beetles, Japanese beetles, European chafers and rose chafers. The larvae are fat and white with brown heads, and are usually found in a curled "C" position. The European and rose chafer grubs are smaller than June beetle grubs. They can become a problem when sod is converted to flower beds. Young bedding plants and seedlings are most severely damaged by root feeding.

Wireworms are the larvae of click beetles, with a hard orange shell, six legs, and a cylindrical body about 2 cm long. As with white grubs, they are often present in new gardens when sod is converted to flower beds. Wireworms cause damage when feeding on the roots of plants.

Management Options

For management options, refer to the White Grubs section of Chapter 4.

White Pine Weevils

A serious pest of eastern white pine, these insects will also attack Norway spruce, Scots and red pine. Open grown white pine (single trees) are particularly susceptible. Evidence of attack first shows in spring as pitch flows from the preceding year's leader. During the summer, new growth is stunted, turns brown and dies; at least two years of terminal growth is killed. As a result, lateral shoots turn upward and the tree becomes forked.

The adult weevil overwinters in litter below the tree, emerging in early spring to lay eggs in the previous season's leader. The white legless grubs feed around the base of the new shoot; larvae pupate and emerge as adults in late summer, feeding on old and new branches until winter.

Management Options

Prune and destroy affected terminal shoots when first noticed in June and July to prevent completion of the life cycle.

Zimmerman Pine Moths

Zimmerman pine moth larvae are grey-green with black heads, and measure 15 mm at maturity. Their feeding causes pitch resin mixed with sawdust-like frass to collect at the branch whorls on the main trunk or on shoots near the terminal branches where the larvae have entered. Individual branches eventually die completely.

Management Options

Remove larvae from pitch masses in June and July. Prune damaged shoots and remove heavily infested trees.

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For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 25 July 2005
Last Reviewed: 28 June 2010