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Plant Pests
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Aphid
Borers
Lacebug
Mealybugs
Mites
Pod Gall Midge
Scale Insects
Snails
Thrips
Weevils
Whiteflies
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Aphid
Description: Aphids are small soft-bodied insects that tend
to cluster on leaves or branch tips. They can be pink, pale
green, yellow, black or other colors. Some species are covered
with white fluffy wax. Because female aphids can produce young
without asexually, populations can increase rapidly. Winged
stages may occur, which disperse to other plants. aphids usually
over-winter as eggs.
Damage: Aphids damage plants by sucking
sap from them. This may result in curling of leaves and stunting
of growth. In severe infestations, branches may die. Because
they injest more sap than they can digest, they often excrete
a sticky sugan substance called honeydew that drips onto objects
underneath. Sooty mold fungus may grow on the honeydew, resulting
in an unattractive blackish coating on the plant that reduces
photosynthesis. Ants are often attracted to and feed uon the
honeydew. In addition to the direct effects of feeding, aphids
may transmit plant viruses that can injure plants.
Management:
Aphids have many natural biological control agents that help
keep them under control. These include lady bird beetles, lacewings
and parasitic wasps, among others. Conserve these natural enemies
by avoiding the application of non-selective applications of
insecticides, where possible.
Aphids are easily controlled
with applications of insecticidal soap or horticultural oil.
These have a minimal effect on beneficial insects.A dormant
oil spray can be used to destroy over-wintering eggs. A number
of other insecticides, such as neem, pyrethrins, acephate, diazinon
and malathion also control aphids.
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Borers
Description: Borers are
larvae of beetles or moths that burrow into the wood of trees
and shrubs. The tunnels interrupt the flow of water and nutrients
through the conducting tissue. The larvae develop and pupate
in their tunnels. Adult insects then leave the plant through
emergence holes that may be visible on trunks or branches. Plants
may ooze sap mixed with sawdust through holes in their bark.
Damage: Attack by borers causes sparse foliage and low plant
vigor. When the burrowing of borers results in girdling of branches
or the trunk, branches or the entire plant may die.
Management:
Plants under stress are more susceptible to borer attack because
healthy plants are often able to defend themselves with pitch
or sap. Borers are attracted to weakened plants. The best control
is to keep plants healthy by providing adequate water and fertilizer.
Painting or wrapping the trunks of young trees may reduce sunburn
damage and borer attack. Insecticides can be applied to the
bark of the trunk and branches to prevent entry of borers. However,
insecticides are ineffective against borers once they are inside
the tree.
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Lacebug
Description: Lacebugs are small insects with transparent lacy
wings. The immature lacebugs are smaller, wingless and spiny
in appearance. Lacebug feeding is accompanied by dark specks
of excrement on the undersides of leaves. Lacebugs are usually
most active in summer.
Damage: Lacebugs feed by sucking
sap from plants. The feeding creates stippled or speckled spots
on leaves that appear bleached because of loss of chlorophyll.
The entire leaf may become bleached. Small brown or black tarlike
spots of excrement are present on damaged leaves.
Management:
If lacebugs have been a problem in the past, eggs and young
nymphs can be destroyed by spraying horticultural oil early
in the year. Lacebugs can be controlled with applications or
insecticidal soap or other insecticides, such as acephate. The
spray should be applied to the undersides of leaves where the
insects congregate. Repeat application may be required.
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Mealybugs
Description: Mealybugs
are insects related to aphids and scale that are covered with
a white cottony or waxy coating. Egg sacs are also covered by
a cottony coating. Mealybugs tend to feed in protected places,
such as on roots, at the base of leaves and in crevices and
are sometimes difficult to detect.
Damage: Mealybugs feed
on plants by sucking sap from them. They excrete a sugary fluid
called honeydew on which sooty mold fungus may grow. Heavy infestations
of mealybugs may cause plant stunting or may kill branches.
Management: Over-wintering mealybugs can be controlled on trees
and shrubs with an application of an oil spray. During the growing
season plants can be treated with insecticidal soap or an insecticide
such as acephate, malathion or diazinon.
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Mites
Description: Spider mites
are small, almost microscopic relatives of spiders that damage
plants by sucking sap from them. They can be detected by the
presence of fine webbing that they make on the undersides of
leaves and small green, red, black or yellow specks that can
be seen moving around when an infested leaf is tapped over a
piece of paper
Damage: The feeding of spider mites produces
small stipple-like yellow spots on leaves. In severe cases,
the entire leaf may become bleached or bronze-colored. Leaves
may turn brown and fall off. Feeding on new leaves may cause
them to curl and become distorted.
Management: Spider mites
are favored by warm, dry, dusty conditions. An occasional misting
or overhead watering may reduce mite numbers. Ladybird beetles,
predatory mites and other beneficial organisms help to control
spider mites. Spider mites can be controlled with an application
of insecticidal soap, horticultural oil or other insecticides
or miticides.
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Pod
Gall Midge
Description: Pod gall midges are tiny flies
whose larvae feed on leaves of honeylocust trees. The small
whitish larvae cause leaflets to develop into podlike galls,
in which the larvae can be found. Adult flies emerge from the
galls.
Damage: The podlike galls turn brown and fall from
the tree. The result can be early defoliation of trees in midsummer.
Repeated attack may cause branches to die.
Management:
Prune dead branches out of trees. Trees can be treated in spring
and again in summer with an insecticide, such as carbaryl.
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Scale Insects
Description: Scale
insects appear as shell-like or waxy bumps on stems or leaves.
They are insects related to aphids, mealybugs and whiteflies
that become attached to plants and suck sap from them. Eggs
are laid under the shell, and when they hatch, the young scale
insects crawl away to a new location, where they become attached
to the plant.
Damage: Though light infestations of scale
may have little effect on a plant, severe infestations may cause
considerable damage to plants. Branches may be killed and the
entire plant may die.
Management: Beneficial insects, such
as parasitic wasps and lacewings help to control scale insects.
Because mature scale insects are protected by their waxy shell,
they are difficult to control with insecticides, and insecticides
may harm beneficial insects. However, an application of dormant
oil during the winter may smother scale. Also, immature crawler
scales can be killed with the application of horticultural oil
or insecticide in spring before they develop their shells.
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Snails
Description: Snails are
mollusks and, like other mollusks, require a moist environment
when they are active. They are usually active at night or during
cool moist periods during the day. Eggs are laid in masses the
soil.
Damage: Snails and slugs are among the most destructive
garden pests. The most damaging snail in the landscape is the
European brown garden snail. In addition to living at soil level,
it will climb up structures and the trunks of trees and shrubs
to feed on foliage. Snails chew irregular ragged holes in leaves,
scar fruits and strip green bark from stems. Entire leaves may
be consumed. Where they travel, they leave slime trails the
may be visible on foliage.
Management: Control snails with
a molluscicide bait. It is most effective when applied to moist
soil. Care must be taken to prevent the bait from being consumed
by pest and wildlife. In small areas, copper strips can be used
as barriers to exclude snails.
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Thrips
Description: Thrips are
tiny elongated insects that can barely be seen on the undersides
of leaves. They may hide in flowers or other protected places
where they are difficult to detect. Adult thrips have wings
and may be brown or black in color. Immature thrips are wingless
and light in color.
Damage: Thrips feed by rasping the
tissue from the surface of plant tissue and sucking up plant
sap. This results in silver-colored, bleached tissue lacking
in chlorophyll, accompanied by black varnishlike spots of excrement.
In addition, feeding by thrips can cause twisting and distortion
of leaves and flowers.
Management: A number of beneficial
insects, such as lacewings feed on immature thrips and help
to keep them under control. They can also be controlled by applying
insecticidal soap, and insecticides, such as rotenone, pyrethrum,
malathion, diazinon and acephate.
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Weevils
Description: Weevils are
beetles with snouts that feed on a wide variety of plants. The
larvae are white grubs that live in the soil and feed on roots.
Some weevils are mainly active at night and are rarely seen
but can be detected by their feeding damage.
Damage: Feeding
damage by weevils may appear as scalloped notches chewed at
the margins of leaves. In more severe cases, leaves may have
many ragged holes or may be sheared off. The feeding by larvae
on roots may result in the slow decline of plants that is often
mistaken for fungal root disease or other problems. Plants may
suddenly wilt and die if grubs girdle the base of the trunk.
Management: Parasitic nematodes are often used to control larvae
in the soil. Foliage can be treated with an insecticide, such
as acephate, and this can also be used as a soil drench around
the base of the plant to control grubs.
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Whiteflies
Description: Whiteflies
tiny white moth-like insects that can be seen feeding on the
undersides of leaves and flying from the leaves when they are
disturbed. The immature form resembles an oval translucent scale
insect and lacks wings. Whiteflies are relatives of aphids,
mealybugs and scale and, like them feed by sucking sap from
plants.
Damage: Feeding by whiteflies causes stunting of
plants and curling and mottling of leaves. They may also transmit
plant viruses. They excrete a sticky sugar substance called
honeydew on which may grow sooty mold fungus.
Management:
Beneficial insects, such as parasitic wasps, help to control
whiteflies. They can be controlled by applying insecticidal
soap, horticultural oil or an insecticide, such as pyrethrum,
neem oil, malathion or acephate.
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