The Online Gardener's Handbook
Chapter 6: Ornamental Plants
Insect Control on Ornamental Plants
Table of Contents
- Bark Beetles
- Birch Leafminers
- Black Vine Weevils, Taxus Weevils and Strawberry
- Emerald Ash Borer
- Birch Dieback (Birch Borers)
- Caterpillar Family
- Leaf Beetles
- Learn More
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 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
Many plants are susceptible to aphid infestations, especially birch,
chrysanthemum, flowering cherry, crabapple, honeysuckle, Norway
maple, linden, rose, spirea, snowball viburnum, willow and flowering
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.
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 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.
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.
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.
For smaller trees, leafminers can be killed by crushing the mines.
Collecting and destroying damaged or fallen leaves can help reduce
Black Vine Weevils, Taxus Weevils and Strawberry
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.
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.
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.
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.
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
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
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
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
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
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
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.
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 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
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
European pine sawflies have dark-greenish bodies
with longitudinal stripes and black heads and appear in late May
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
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.
Remove individual colonies by hand and destroy whenever possible.
Some of these insects have natural enemies which help keep populations
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
Clip hedges and individual plants before June, and destroy the
clippings. This reduces the insect population before adult moths
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.
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 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.
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 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.
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.
In most cases, no control is recommended beyond removing the galls
and destroying them.
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.
Trap grasshoppers in jars partially filled with molasses.
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.
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.
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.
If populations are not too high, crush leaves between fingers to
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.
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.
Hand pick and destroy adults and larvae. Inspect undersides of
leaves for eggs and crush. Inspect transplants for signs of beetle
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.
Twigs where eggs have been laid can be pruned out in fall or early
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.
Not usually required.
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
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.
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
Leafminer populations vary from year to year, and may not be significant
enough to warrant control.
Follow proper sanitation procedures. Remove and destroy all prematurely
fallen leaves and any leaves where symptoms are evident.
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.
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
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.
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 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.
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.
Whenever possible, remove infested shoots by hand in late May and
early June and destroy them. Young trees less than 20 m are the
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
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.
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.
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
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.
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.
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.
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.
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
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.
Pick off and destroy. Spittlebugs can be washed off plants with
a strong jet of water.
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.
Not usually required.
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.
Remove and destroy flowers with thrips present. Damage may be less
severe when bulbs are planted early.
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.
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
For management options, refer to the White Grubs section of Chapter
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.
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.
Remove larvae from pitch masses in June and July. Prune damaged
shoots and remove heavily infested trees.