BIOLOGICAL COMPETITORS
Significance of Pests
Modern agriculture is largely a
Monoculture
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Efficent but . . .
May encourage pest buildups
Chemical vs. Biological Control
Developed countries depend on
chemicals . . .
Ideally, long-term control is based on
biological methods
Numerous techniques
Chemical Pest Control History
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Late 19th century
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Bordeaux mixture on vineyards
Iron sulfate
Early 20th century
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Application equipment
1904 power sprayer (Germany)
 Aerial application in 1921 (U.S.)
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New Chemistry
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War-time chemicals
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Three chemical classes around WWII
 Organophosphorus insecticides
 Dithiocarbamate fungicides
 Phenoxy herbicides
DDT (1939)
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Dichloro-diphenyl-trichloroethane
Insecticide controlled fleas, lice, mosquitos
Odorless, grayish-white powder
Banned in U.S. in 1972-73 (environment)
Biological Techniques
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Resistant plant types
bred/engineered
Natural enemies
Sterile male release
Attactants including pheromones
Juvenile hormones
Insects feeding on weeds (not crops)
Antagonistic fungi/bacteria
Integrated Pest Management
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IPM (Integrated Pest Management)
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implies that no single control
procedure will control a pest
successfully...
IPM seeks to:
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Integrate a variety of physical,
biological, and chemical methods
to control pests
Integrated Pest Management
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In IPM:
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natural controls are emphasized
artificial controls are used only as
required
potentially harmful species
continue to exist at tolerable levels
WEEDS
A weed is any plant growing out of
place!
Weeds compete with crops for:
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Space
Water
Mineral nutrients
Sunlight
WEEDS (cont)
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Annuals vs. Perennials
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Control methods vary
Annuals – focus on preventing seeding
Perennials – seed and underground parts
Means of control:
 Pulling
 Hoeing
 Mechanical (tillage, mowing, etc.)
 Chemical
 Mulching
 Fire
MODERN WEED CONTROL
Early 1940’s
Mechanical control alone expensive!
Four basic methods of control
developed:
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4)
Preventative measures (prevent seed)
Crop competition (good shades bad)
Biological control (natural enemies)
Chemical control
1930’s – study of auxins
1940’s – synthetic auxin 2,4-D (herbicide)
Chemical Weed Control
Chemicals classified as:
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Selective
Nonselective
Selective kills certain kinds of weeds
e.g. broad-leaved vs. grasses
Nonselective kills all vegetation it is
applied to
Chemical Weed Control (cont)
Herbicides also classified by:
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Timing of application related to growth cycle
of weeds or crops
• Preplant
• Preemergence
• Postemergence
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Method of application
• Broadcast
• Banding
• Spot treatment
Types of Weeds
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Annuals
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Biennials
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Complete life cycle in one year; seeds
Seeds germinate 1st spring, grow
vegetative 1st summer, winter chill,
flower 2nd spring, seeds 2nd summer
Perennials
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Can live indefinitely; seeds and
vegetative (root, rhizome, stolon, tuber)
Plant Diseases and Insects
Annual losses in crops, ornamentals,
and turf hundreds of billions $$
Methods of control fall into four groups
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Biological control
Cultural practices
Government quarantine/eradication
programs
Application of pesticides
Plant Diseases
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Disease (dis - ease)
Plant condition which is abnormal as a
result of an infectious pathogen
Three (3) major groups:
Bacteria
 Fungi
 Viruses
Also: mycoplasmas, parasitics
(including nematodes)
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Plant Diseases (cont)
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Infectious diseases require:
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Susceptible host
Causal agent
Favorable environment for pathogen
Appearance requires primary inoculum
(portion of pathogen)
Symptoms may appear when inoculum :
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penetrates and becomes established in the host
sets up a life cycle including the host
Plant Diseases (cont)
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Disease symptoms:
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Abnormal tissue coloration
Wilting
Tissue death
Defoliation
Abnormal increase in tissue size
Dwarfing
Replacement of host plant tissue by
tissue of the infectious organism
Pathogens of Infectious Diseases
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Bacteria
Fungi
Viruses
Mycoplasmas
Parasitic plants
Nematodes
Pathogens of Infectious Diseases
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Bacteria
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Both beneficial and pathogenic
Bacterial diseases difficult to control
Resistant plant species, cultivars, seeds
Spread by rain, wind-blown dust, birds,
insects, poor cultural techniques
Moisture aids entry into plants through
stomata, scars, wounds
Chemical control limited effectiveness
Pathogens of Infectious Diseases
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Fungi
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Both beneficial and pathogenic
Obtain nutrients from other sources
Some live on dead O.M. – others live
on living tissues; facultative on either
Beneficials decompose dead matter
Mycorrhiza – symbiosis with plant roots
Other beneficials: penicillium, bread,
cheese, and alcohol production
Pathogens of Infectious Diseases
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Most plant diseases caused by fungi
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Famines, blights, epidemics, starvation
Mycelium consist of thread-like hyphae
Hyphae absorb food from host
Fungi reproduce by spores
Fungal diseases usually easier to control than
bacterial or viral diseases
Control by:
 resistant varieties, proper sanitation, crop
rotation and other cultural practices,
fungicides, and antagonistic fungi
Pathogens of Infectious Diseases
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Viruses
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Extremely small (electron microscope)
Outer protein shell, inner nucleic acid
Depend on living cell in order to grow
Depend on transmitting vector carrier to move
from plant to plant
Named for the disease they cause
Control by resistant varieties
Chemicals only control insect vectors
Heat therapy renders some viruses inactive
Propagate virus-free plants from shoot tips
Pathogens of Infectious Diseases
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Mycoplasmas
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Similar to animal mycoplasmas
Intermediate size between virus and bacteria
Cells have three-layered membrane
Have own energy and enzyme system
Occur in phloem, disrupt food transport
Named after plant first infected
Transported by vectors
Control by eliminating vectors
Certain antibiotics are effective (tetracycline)
Pathogens of Infectious Diseases
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Parasitic Plants
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Three groups:
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Epiphytes
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Hemiparasites
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Little harm; physical support
Spanish moss, epiphytic orchid
Do harm; water and mineral nutrients
Can photosynthesize carbohydrates
Witchweed, Mistletoe
True parasites
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Lack chlorophyll; depend entirely on host
Dwarf mistletoe, Dodder, Broomrape
Pathogens of Infectious Diseases
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Nematodes
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A.K.A. threadworms, roundworms, and
eelworms
Attack roots, stems, foliage, inflorescence
plant parasitics approx. 1 mm long
damage by piercing/puncturing/injecting
secretions
classified by visible effects caused to
plants...
Pathogens of Infectious Diseases
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Nematodes (cont)
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root knot
cyst
lesion
stubby-root
also spread certain viruses/diseases
Various methods to reduce crop losses
from nematodes:
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Resistant species/cultivars, Nematodefree stock/soil, fumigate soil, Nematicides
Insects and Mites
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Compete with humans for food
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Also spread disease
Not all are bad; predators, beneficials
Praying mantis, ladybird beetle, green
lacewing, predatory Aphytus wasp
 Honeybee, silkworm
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Some are eaten
Some for research
Control essential – world food supply
Insects and Mites
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Control methods
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Biological
Cultural
Physical/mechanical
chemical
Insects and Mites
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Classification of Insects
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Order
Metamorphosis
Chewing/sucking
additional damage by:
egg laying
 spread of disease
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Insects and Mites
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Action of pesticides control
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Stomach poison
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Systemic action kills chewing/sucking
Contact action
Fumigation
Suffocation
Dessication
Repellant action
Attractant action
Hormone action