BIOLOGICAL COMPETITORS
Significance of Pests
Modern agriculture is largely a
Monoculture
• 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
Late 19th century Bordeaux mixture on vineyards Iron sulfate
Early 20th century Application equipment
1904 power sprayer (Germany) Aerial application in 1921 (U.S.)
New Chemistry
War-time chemicals Three chemical classes around WWII
Organophosphorus insecticides Dithiocarbamate fungicides Phenoxy herbicides
DDT (1939) Dichloro-diphenyl-trichloroethane Insecticide controlled fleas, lice, mosquitos Odorless, grayish-white powder Banned in U.S. in 1972-73 (environment)
Biological Techniques
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
IPM (Integrated Pest Management) implies that no single control
procedure will control a pest successfully...
IPM seeks to: Integrate a variety of physical,
biological, and chemical methods to control pests
Integrated Pest Management
In IPM: 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:• Space• Water• Mineral nutrients• Sunlight
WEEDS (cont)
Annuals vs. Perennials 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’sMechanical control alone expensive!Four basic methods of control developed:
1) Preventative measures (prevent seed)2) Crop competition (good shades bad)3) Biological control (natural enemies)4) Chemical control
1930’s – study of auxins1940’s – synthetic auxin 2,4-D (herbicide)
Chemical Weed Control
Chemicals classified as:• Selective• Nonselective
Selective kills certain kinds of weedse.g. broad-leaved vs. grasses
Nonselective kills all vegetation it is applied to
Chemical Weed Control (cont)
Herbicides also classified by:
• Timing of application related to growth cycle of weeds or crops
• Preplant• Preemergence• Postemergence
• Method of application• Broadcast• Banding• Spot treatment
Types of Weeds
Annuals Complete life cycle in one year; seeds
Biennials Seeds germinate 1st spring, grow
vegetative 1st summer, winter chill, flower 2nd spring, seeds 2nd summer
Perennials 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• Biological control• Cultural practices• Government quarantine/eradication
programs• Application of pesticides
Plant Diseases
Disease (dis - ease) Plant condition which is abnormal as a
result of an infectious pathogen Three (3) major groups:
Bacteria Fungi VirusesAlso: mycoplasmas, parasitics
(including nematodes)
Plant Diseases (cont)
Infectious diseases require: Susceptible host Causal agent Favorable environment for pathogen
Appearance requires primary inoculum (portion of pathogen)
Symptoms may appear when inoculum : penetrates and becomes established in the host sets up a life cycle including the host
Plant Diseases (cont)
Disease symptoms: 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
Bacteria Fungi Viruses Mycoplasmas Parasitic plants Nematodes
Pathogens of Infectious Diseases
Bacteria 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
Fungi 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
Most plant diseases caused by fungi 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
Viruses 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
Mycoplasmas 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
Parasitic Plants Three groups:
Epiphytes Little harm; physical support Spanish moss, epiphytic orchid
Hemiparasites Do harm; water and mineral nutrients Can photosynthesize carbohydrates Witchweed, Mistletoe
True parasites Lack chlorophyll; depend entirely on host Dwarf mistletoe, Dodder, Broomrape
Pathogens of Infectious Diseases
Nematodes 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
Nematodes (cont) root knot cyst lesion stubby-root also spread certain viruses/diseases Various methods to reduce crop losses
from nematodes: Resistant species/cultivars, Nematode-
free stock/soil, fumigate soil, Nematicides
Insects and Mites
Compete with humans for food Also spread disease Not all are bad; predators, beneficials
Praying mantis, ladybird beetle, green lacewing, predatory Aphytus wasp
Honeybee, silkworm Some are eaten Some for research
Control essential – world food supply
Insects and Mites
Control methods Biological Cultural Physical/mechanical chemical
Insects and Mites
Classification of Insects Order Metamorphosis Chewing/sucking additional damage by:
egg laying spread of disease
Insects and Mites
Action of pesticides control Stomach poison
Systemic action kills chewing/sucking Contact action Fumigation Suffocation Dessication Repellant action Attractant action Hormone action