Pests
Pests
There are many kinds of pests. Each structure, crop, or animal have
pests. You must recognize or be able to identify the common pests that you work
with and their hosts. Otherwise, you may use the wrong method of control, choose
the wrong pesticide, or treat too early or too often and do more harm than good.
(See Chapter XI, IPM)
If you know the general pattern of the pest's life cycle, the damage it does,
and when it does the damage, it will help you to:
- know the best time to control the pest.
- use less pesticide, or use other methods of control.
- avoid injury to the host (plant or animal).
- avoid injury to non-target areas.
Never guess at your pest problems.
Goals of This Chapter
- Be able to recognize pests by identifying physical characteristics and damage.
- Understand how different pests reproduce and develop.
- Be familiar with how diseases affect plants.
Pests
Human civilization has been competing with insects, rodents, diseases, and weeds
for survival throughout its history. Historical records of plagues, famine, and
pestilence fill volumes of texts. Modern man has, through his technology,
created tools to combat these pests. The use of a tool, such as a pesticide,
depends on the applicators ability to know when they are needed. Proper
identification of the problem is the first step to proper application.
A pest is considered to be anything that:
- injures humans, animals, crops, structures, or possessions.
- competes with humans, domestic animals or crops for food, feed, or water.
- spreads disease to humans, domestic animals, or crops.
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The certified applicator must know the pests that are most likely to be
encountered. To be able to control these pests, you need to know the following:
- the common features of pest organisms.
- characteristics of the damage they cause.
- the biology and development of the pest.
Pests can be placed into four main categories:
- insects and closely related animals
- plant diseases
- weeds
- vertebrates
Insects
Insects, as a class of animals, outnumber all other living animals on earth.
There are three times as many insects as there are animals in the rest of the
animal kingdom. Insects are found everywhere; in snow, water, air, soil, hot
springs, and in or on plants and animals. They compete with man and animals for
food and are also considered food for a significant number of other animals.
Some insects survive solely by feeding on man, for example human lice, and
cannot survive for long if removed from the human body. Insects are an extremely
important part of the earth's ecosystem, and despite our dread of insects we
could not survive without them.
The certified applicator controlling insects must be more knowledgeable of
insects than the average person. Insects can be divided into three groups by
their importance to man:
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Insect Body Characteristics
All adult insects have two characteristics in common; they have three pairs of
jointed legs, and they have three body regions - the head, thorax, and abdomen.
Head. Attached to the insect head are the antennae, eyes, and mouthparts.
All of these parts vary in size and shape, and can be helpful in identifying
some pest insects.
Antennae are paired appendages usually located between or below the eyes.
Antennae vary greatly in size and form and are used in classifying and
identifying insects. Some of the common antennae types are:
- filiform - threadlike; the segments are nearly uniform in size and shaped like
a cylinder (ground beetle, cockroach).
- moniliform - look like a string of beads; the segments are similar in size and
round in shape (termites).
- serrate - sawlike; the segments are more or less triangular (click beetle).
- clubbed - segments increase in diameter away from the head (Japanese beetle).
- plumose - feathery; most segments with whorls of long hair (male mosquito)
Mouthparts are different in various insect groups and are often used in
classification and identification. The type of mouthpart determines how the
insect feeds and what sort of damage it does. It is important that the
applicator have some knowledge of the these types of insect mouth parts:
Thorax. The thorax, or middle body segment, has three pair of legs and
sometimes one or two pair of wings (forewings, hindwings).
Legs come in many sizes, shapes, and functions and are helpful in
identifying insects. Used for walking, running, jumping and climbing, legs have
become very specialized in some insects like the large jumping leg in the
grasshopper. Crickets and long -horned grasshoppers have an eardrum at the base
of one of their leg segments.
Wings also vary in size, shape, and texture. The pattern of veins on the wings
of an insect are often used to identify insect species. Forewings in some
insects are hard and shell-like, as in beetles. The grasshoppers have forewings
that are leathery. The forewings of flies are thin, clear, and like membranes.
The wings of moths, butterflies, and mosquitoes are membranous and are also
covered with scales.
Abdomen. The abdomen of the insect is built of segments. Along the side
of the segments are openings, called spiracles, which the insect uses to
breathe. The abdomen contains digestive and reproductive organs. Parts of the
abdomen used in identification include: the ovipositor, male genitalia, and
cerci.
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Insect Reproduction and Development
Insect reproduction. In most insects, reproduction results from the males
fertilizing females. The females then lay the eggs. This is the pattern of life
for most insects, but there are a few interesting variations. For example, some
parasitic wasps produce eggs without ever mating. In some of these species,
males are unknown. There are a few insects that give birth to live young,
without the egg stage.
Egg hatching is affected by temperature, humidity, and light. Eggs come in
several shapes (round, oval, flat, and elongate) and sizes. They are laid one at
a time, in groups, and in floating rafts. Some insects lay eggs in capsules
containing several eggs, then carry them until hatching to be sure of the
survival of their young (German cockroach). Sometimes eggs are placed inside the
bodies of animals, trees, and green plants. In some species, the eggs are used
to identify the adult. For example, the egg capsules of cockroaches can be used
to identify an infesting species of cockroach.
Insect Metamorphosis (development). Insects go through a series of
changes as they develop from the egg to adulthood. This process of growth is
called metamorphosis.
After hatching from an egg, the young insect is called either a larva, nymph, or
naiad. The young feed for a while and grow. When they grow to a point where the
skin cannot stretch further, the young insect molts and a new skin is formed.
These stages of growth and skin shedding (called instars) differ from insect to
insect and sometimes may vary with the temperature, humidity, and food supply.
Generally, the heaviest feeding occurs in the last two instars. There are four
types of metamorphosis:
The larvae hatch from an egg. As they grow larger they molt and pass through one
to several instars. Larvae come in several forms, shapes, and sizes such as
caterpillars with many legs to maggots which are legless.
The pupa is often called the resting stage, but the insect is doing anything but
resting. While in this stage, the larvae changes into an adult with legs, wings,
antennae, and a fully functional reproductive system.
Insect-Like Pests
Spiders, ticks, mites, sowbugs, pillbugs, millipedes, and centipedes resemble
insects in habit, appearance, life cycle, and size. Although they are not
insects, they are often mistaken for them. The pesticide applicator needs to be
familiar with these pests when evaluating a problem.
Centipedes and Millipedes.
Centipedes are flat, long, worm-like animals, with each body segment having one
pair of legs. They have chewing mouthparts. Some can give painful bites to
humans. Centipedes are found in protected places under tree bark or in rotting
logs. They are very fast and predaceous, capturing and feeding on insects,
spiders, and other small animals. All centipedes have poisonous jaws.
Millipedes have a cylindrical shape, like an earthworm, and have many legs, two
pair on each body segment. The mouth parts are adapted to feeding on decaying
organic material. Thus, they are found in decaying leaf litter, rotting logs,
and near damp debris near foundations.
Millipedes and centipedes have no metamorphosis. They only change in size
between hatching from the egg and reaching the adult stage.
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Insects and Injury
Crustaceans. This class of animals (lobsters, shrimp) are nearly all
aquatic (living in water) but there are members living on land that may become
pests and are often thought to be insects. Sowbugs (often called pillbugs) are
black, gray, or brown and are capable of rolling up into a ball. Sowbugs are
found in damp decaying wood or under objects such as stones, boards, or blocks.
There have been cases when crustaceans have been considered pests of cultivated
plants in some areas, but usually are found living in damp basements or garages
where people don't want them.
Arachnids. This group, which consists of spiders, mites, ticks, and
scorpions all have eight legs and only two body regions. Arachnids are wingless
and lack antennae. They mature through gradual metamorphosis that includes both
larval and nymphal stages. Eggs hatch into larvae (six legs) which molt into
nymphs (eight legs) and then adults. Spiders and scorpions have chewing
mouthparts. Ticks and mites have a modified version of piercing -sucking
mouthparts. Ticks are of particular interest because they sometimes transmit
diseases such as Lyme disease and Rocky Mountain Spotted fever to man during
feeding.
Plant Diseases
A plant disease is any harmful condition that alters a plants growth,
appearance, or function. Diseases are caused by biological agents called
pathogens. They are of interest to pesticide applicators because some diseases
can be cured with pesticides, while other pesticides can prevent the pathogen
from infecting the host plant. Pathogens include bacteria, fungi, viruses, and
nematodes. They are spread by wind, rain, insects, birds, snails, slugs, and
earthworms. In addition, pathogens can be carried by transplanted soil, nursery
grafts, vegetative propagation, contaminated equipment and tools, infected seed,
pollen, dust storms, irrigation water, and people.
Plant pathogens are parasites which live and feed on the host plant. In order
for a disease to develop, a pathogen must be present, the host plant must be
susceptible, and the environment must be favorable for development of the
pathogen. Temperature and moisture are especially important to the success of
the pathogen.
The disease starts with the arrival of the pathogen on the plant. If the
parasite can get into the plant, the infection starts. Three main ways a plant
responds to a disease are:
- overdevelopment of tissue, galls, swellings, and leaf curls.
- underdevelopment of tissue, stunting, lack of chlorophyll, and incomplete
development of organs.
- death of tissue, blights, leaf spots, wilting, and cankers.
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Bacteria. Bacteria are microscopic (can only be seen with a microscope),
one-celled organisms that reproduce by single cell division. Bacteria numbers
multiply quickly under warm, humid weather conditions. Bacteria may attack any
part of a plant, either above or below the soil surface. Several of the leaf
spot and rot diseases are caused by bacteria.
Fungi. Fungi are plants that lack chlorophyll and cannot make their own
food. Fungi are the most frequent pathogens on plants. They feed off other
living organisms or live on dead or decaying organic matter. Most of the time
fungi are beneficial because they help release nutrients from dead plants and
animals, adding to the fertility of the soil. Fungi reproduce with spores, which
function about the same way seeds do. Fungus spores are usually microscopic and
are produced in high numbers. Most spores die because they do not find a host to
feed on, though some can survive for months without a host. High humidity (above
90 percent) is essential for spore germination and active growth. Mildew and
smut are good examples of fungal diseases.
Viruses. Viruses are tiny organisms smaller than bacteria and cannot be
seen with an ordinary microscope. Viruses are usually recognized from the
symptoms they induce on the infected plant. They depend on other living
organisms for food and cannot live long on their own. Viruses invade healthy
plants through wounds or during pollination. Insects that feed with
piercing-sucking mouthparts (aphids, whiteflies, leafhoppers), as well as
chewing insects (beetles) can transmit viruses while feeding. Viruses can also
be spread by nematodes. Practically all plants can be infected by viruses.
Mycoplasmas are the smallest known independently living organisms. Unlike
viruses, they can exist apart from the host organism. Mycoplasmas obtain their
food from plants. Yellows disease and some stunts are caused by mycoplasmas.
Nematodes. Nematodes are tiny (microscopic) eel or worm-like organisms.
Nematodes destroy root systems while feeding, which causes a loss in the uptake
of water and minerals by the p lant, thus weakening the plant. Common symptoms
are wilting, stunting, and lack of vigorous growth under good growing
conditions. Nema todes may also spread plant diseases while feeding. Nematodes
feed by sucking the contents of a cell through a hypodermic-like mouth inser ted
into a cell. Not all nematodes feed on roots. Some foliar feeding n ematodes
attack chrysanthemums and leave triangles of brown, dried tissue that develop on
the leaves late in the season. Some nematodes are parasitic to insects.
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Weeds
Any plant can be considered a weed when it is growing where it is not wanted.
This is a very broad definition, but consider the following problems caused by
weeds.
Weeds can harm man by:
- causing skin irritation (poison ivy).
- causing hay fever (ragweed).
- harboring pests such as rodents, ticks, or insects.
Weeds can harm desirable plants by:
- releasing toxins in the soil which inhibit the growth of desirable plants.
- contaminating the product at harvest.
- competing for water, nutrients, light, and space.
- harboring pest insects, mites, vertebrates, or plant disease agents.
Weeds can harm grazing animals by:
- poisoning.
- causing an "off-flavor" in milk and meat.
Weeds may become pests in water by:
- hindering fish growth and reproduction.
- increasing mosquito reproduction.
- hindering boating, fishing, and swimming.
- clogging irrigation ditches, drainage ditches, and channels.
Weeds are dangerous and undesirable on rights-of-way because they:
- block vision, road signs, and crossroads.
- increase road maintenance costs.
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Plant Development Stages
After a plant seed has germinated, development can be separated into four
stages:
Duration of the Weed
Annuals. Plants that grow from seed, mature, and produce seed for the
next generation in one year or less are called annuals. This group has many
grass-like weeds (crabgrass) and broadleaved (pigweed) m embers. There are two
basic types of annual weeds:
-
Summer annuals grow from seeds that sprout in the spring. These weeds
grow, mature, produce seed, and die before winter. Some examples are: foxtail,
pigweed, lambsquarters, and crabgrass.
-
Winter annuals grow from seeds which sprout in the fall. These weeds
mature, produce seed, and die before the next summer. Some examples are: henbit,
common chickweed, and annual bluegrass.
Biennials. These plants have a two-year life cycle. During the first
year, they grow from seed and develop a heavy root and compact cluster of leaves
(called a rosette). During the second year, they mature, produce seed, and die.
Some examples are: bull thistle and burdock.
Perennials. When plants live more than two years they are called
perennials. Perennials may mature and reproduce in the first year, but they will
repeat the cycle for several years or maybe indefinitel y. Some perennial plants
die back each winter. Others, such as trees, may lose their leaves but do not
die back. Most perennials grow from seed and many produce tubers, bulbs,
rhizomes (below-ground root-like stems), or stolons (above-ground stems that
produce roots).
-
Simple perennials usually reproduce with the use of seeds. They also may
reproduce when root pieces are cut by cultivation. The pieces then grow into new
plants. Examples: trees, shrubs, plantain, and dandelions.
-
Bulbous perennials may reproduce by seed bulblets, or bulbs. Wild garlic
produces seed and bulblets above ground and bulbs below ground.
-
Creeping perennials produce seed, rhizomes (below-ground stems), or
stolons (above-ground stems that can produce roots). Examples: Johnsongrass,
field bindweed, and Bermudagrass.
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Weed Identification
Arrangement of Leaves
-
Alternate - one leaf found at each level on the stem.
-
Opposite - two leaves opposite each other or paired.
-
Whorled - three or more leaves at each level on the stem.
Leaf Structure
-
Simple - the leaf blade is a single piece and not divided into separate
leaflets.
-
Compound - the leaf blade is divided into several leaf-like parts called
leaflets.
Leaf Shape
-
Ovate - Egg-shaped, elliptical, broadest at the base.
-
Lanceolate - lance-shape, are longer than ovate and usually pointed at
the tip.
-
Linear - long and narrow with parallel sides (grasses).
Arrangement of the Flowers
-
Inflorescence - in a definite cluster, usually at the top of the plant.
-
Axillary - along the stem of the plant in the angles (leaf axils) between
the foliage, leaves and the stem.
Flower Parts
-
Petals - the expanded and usually colorful parts of the flower.
-
Sepals - the greenish hull surrounding the flower when it is budding.
Major Classes of Weeds
Grasses. Leaves of grasses are narrow, stand upright, and have parallel
veins. When the seedlings sprout, they have only one leaf. Grasses grow from a
point (growing point) located below the soil surface, thus the growing point is
sheltered. This is why grass can be mowed without killing the plant. Most
grasses have fibrous root systems. Grasses have both annual and perennial
species.
Sedges. These are similar to grasses, but they have triangular stems and
three rows of leaves. They are sometimes listed under grasses on the pesticide
label. These plants often are found in wet places, but are principal pests in
fertile, well-drained soils. Yellow and purple nutsedge are perennial weed
species and produce rhizomes and tubers.
Broadleaves. Seedlings of broadleaves have two leaves that emerge from
the seed. The veins of their leaves are netlike. Broadleaves usually have a
taproot and their root system is relatively coarse. All broadleaf plants have
exposed growing points that are at the end of each stem and in each leaf axil.
The perennial broadleaf plants may also have growing points on roots and stems
above and below the surface of the soil. The broadleaves have species with
annual, biennial, and perennial life cycles.
Vertebrate Pests
Vertebrate animals all have a jointed backbone. Humans are vertebrates, as are
mammals, birds, reptiles, amphibians, and fish. Like insects, most vertebrate
animals are not pests and can be an enjoyable part of our environment.
There are situations when vertebrates can be pests. Sometimes birds, rodents,
raccoons, or deer may damage crops or ornamentals. Birds and rodents eat the
same food as humans and often ruin more food than they eat. Mammal and bird
predators of livestock and poultry cause financial losses to farmers and
ranchers each year. Great flocks of roosting birds can soil buildings.
There are also those in the vertebrate group (particularly rodents) that are a
hazard to public health when they are in homes, restaurants, offices, or
warehouses. Rodents, other mammals, and some birds are potential reservoirs of
serious diseases of humans and domestic animals. Some examples are: rabies,
plague, and tularemia.
Fact and picture sheets are a handy and easy to use aid for identifying
vertebrate pests. You can obtain them through Cooperative Extension or other
professional associations.
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