Upload
milton-cooper
View
227
Download
0
Tags:
Embed Size (px)
Citation preview
Pesticides
What is a pest?What is a pest? An organism that interferes with human
welfare and activities Insects Weeds
Why do we need Why do we need pesticides?pesticides?
Insects eat and destroy crops
Weeds compete with crops
Insects carry disease
Benefits of pesticidesBenefits of pesticides Allows more food production
Farmers can save $3-$5 in crops for every $1 invested in pesticides
Protects people from disease
DDT used to fight DDT used to fight MalariaMalaria
Sri Lanka in the early 1950’s, more than 2 million cases of Malaria
Began spraying DDT to kill the mosquitos carrying the disease
Cases dropped to 0
Discontinued spraying and malaria cases jumped up to 1 million per year
Began spraying again and still do in over 20 tropical countries
DisadvantagesDisadvantages Often kill non-target species
Pesticide residue on crops
Persistent in environment- affects animals up the food chain
People working closely with pesticide at risk of health problems
Types of PesticidesTypes of Pesticides Chemical pesticides
Not naturally occurring Toxic Persistent in the environment Affect non-target species Examples- Crabamate Pesticides,
Organochlorine pesticides (DDT), Organophosphate pesticides
Chemical PesticidesChemical Pesticides Crabamate Pesticides
Affects non-target species Affect the nervous system Effects are usually reversible
Organophosphate Pesticides Affect the nervous system Affects non-target species Highly toxic Not as persistent in the environment
Chemical PesticidesChemical Pesticides
Organocholorine Insecticide Very persistent in the environment Affects non-target species Effects nervous system Removed from the market due to health effects Examples include DDT
Organic pesticidesOrganic pesticides Naturally occurring in the environment
Plants have developed natural resistance to pest Can be used naturally or made synthetically
Easily degradable in environment
Not persistent
Can be toxic to aquatic organisms and pollinators
BiopesticidesBiopesticides
Microbial pesticides Made from microorganisms - fungi and bacteria
Plant-incorporated protectants Genetically alter plant to produce its own pesticide
Biochemical Naturally occurring substances that control pests
Major problems with Major problems with PesticidesPesticides
Pest species (plant and animal) develop resistance to pesticides
Pesticides that don’t degrade easily can cause problems for humans and other organisms
Bioaccumulation - build up of pesticides in body
Biomagnification - organisms higher up in the food web have higher concentrations of pesticides in their body
AlternativeAlternative Integrated Pest management
Integrated Pest Integrated Pest Management (IPM)Management (IPM)
A general philosophy of safe & effective pest control that uses several different methods of control to reduce the population of a particular pest
Involves identifying & understanding each pest, its life cycle, breeding sites, and density threshold (# of pests per area that can be tolerated without overall crop damage) & selecting remedies that address the specific pest problem
Six Steps of IPM
1. Implement preventive strategies.
2. Scout plants for symptoms or presence of pests.
3. Identify pests and scope of damage.
4. Determine when action must be taken.
5. Implement management strategies.
6. Evaluate results.
Steps of Integrated Pest Management
Integrated Pest Integrated Pest Management (IPM) Management (IPM)
StrategiesStrategies Development of resistant varieties: some plants are
naturally resistant to insects, some produce their own pesticides, some produce odors that discourage pests, some produce chemicals that interfere with an insect’s nervous system and some contain chemicals that make an insect unable to digest food
Resistant varieties reduce the need for spraying synthetic pesticides
Developing resistant varieties in time consuming & expensive
Integrated Pest Integrated Pest Management (IPM) Management (IPM)
StrategiesStrategies Use of Beneficial Insects: beneficial wasp species
are the most useful insects for controlling the populations of important insect pests such as gypsy moth larvae, cutworms boll weevils, hornworms, and mealy bugs
Introduction of the Paraguayan wasp, a parasite of the mealy bug, helped to protect Cassava (an important food crop in Africa)
Not all insects are good biological controls – praying mantises are not selective & will eat all insects, not just the pests
Integrated Pest Integrated Pest Management (IPM) Management (IPM)
StrategiesStrategies Microbial pesticides: viruses, protozoa, bacteria &
fungi can be used to control certain insect pests
Bacillus popillae is a bacterium that causes milky spore disease in Japanese beetles; it is sprayed on the soil where the beetle larvae live & when the larvae die, the bacterial spores are released into the soil & continue to control the beetle larvae
It is expensive to establish the spores that cause milky spore disease and it is only effective if the entire neighborhood uses it
Integrated Pest Integrated Pest Management (IPM) Management (IPM)
StrategiesStrategies Biochemical pesticides: use naturally occurring substances
that control pests by nontoxic methods, such as pheromones
Pheromones are sex attractants that can be used to bait traps; synthetic sex attractants have been produced and used to control fruit flies in Florida & California
Cannot be used on all species – there is no practical or economical way to hang dispensers containing female pheromones high in forest trees, where they are needed to control gypsy moths
The correct distribution of pheromone is necessary to disrupt the mating process
Integrated Pest Integrated Pest Management (IPM) Management (IPM)
StrategiesStrategies
Cultivation Practices: timing the planting and harvest to avoid pests can reduce damage to some crops
Mixing crops - reduce monocultures
Delaying the planting of wheat prevents Hessian flies from laying eggs on young wheat plants
Plowing under the cover crop residue of cotton eliminates winter habitat for insect pests such as the boll weevil
Integrated Pest Integrated Pest Management (IPM) Management (IPM)
StrategiesStrategies
Synthetic Pesticides: SLAM is a low-insecticide bait made from powdered wild buffalo gourd root and carbaryl insecticide (one ounce per acre); these chemicals are like candy to the rootworm beetle and they eat so much of it that it takes little insecticide to kill them – farmers only spray when needed
Biological controls have significantly reduced the amount of synthetic pesticides used but they have not replaced the use of pesticides entirely
Integrated Pest Integrated Pest Management (IPM) Management (IPM)
StrategiesStrategies
Computer Programs: help farmers reduce the amount of pesticides they use
Spraying only when the number of insects will reach damaging levels (not when few insects present)
Spraying only when the insect is in its larval stage (not after the cocoon is spun = too late)
Benefits of Biological Benefits of Biological ControlsControls
Usually cheaper to use than chemical controls
Don’t pollute the environment
Often kill only the pest, not beneficial insects
Disadvantages of Disadvantages of Biological ControlsBiological Controls
Biological controls are often more expensive to develop (must travel to country of origin to find natural predators & diseases – bring back & study under quarantine)
Less profit for companies – companies will not invest time & money on research without a financial incentive
Effective biological controls for many insect pests are not yet available
Disadvantages of Disadvantages of Biological ControlsBiological Controls
Some biological controls require cooperation of surrounding neighbors in order to be effective
Some farmers are unwilling due to the ease of using chemical pesticides
Biological controls are slow-acting whereas chemical pesticides are fast acting