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PESTICIDES Adapted from K. Sturges

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Page 1: Pesticides - ms-kellys-universe.weebly.com · Pests and Pesticides PROBLEMS WITH PESTICIDES: Many pest species evolve resistance Pesticides affect more than the target pests Pose

PESTICIDES

Adapted from K. Sturges

Page 2: Pesticides - ms-kellys-universe.weebly.com · Pests and Pesticides PROBLEMS WITH PESTICIDES: Many pest species evolve resistance Pesticides affect more than the target pests Pose

Pests and Pesticides

◦ A Pest- any organism that damages crops valuable to us

◦ interferes with human welfare or activities

◦ Weed- any plant that competes with crops

◦ To suppress pests and weeds we have developed thousands of

chemicals to kill insects, plants and fungi.

◦ Called pesticides

◦ Roughly 400 million kg ( 900 million lbs) applies in the US each year

◦ $32 billion spend annually (1/3rd of that spent in the US)

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Pests and Pesticides

◦ The ideal pesticide would be◦ narrow-spectrum

◦ Only kill target pest

◦ Readily broken down into safe materials

◦ Stay exactly where it was put/not move around

◦ Not create genetic resistance or “super pests”

◦NO SUCH THING!

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Pests and Pesticides

◦Most pesticides:◦ Are broad-spectrum

◦ Kill target pest along with other, unintended organisms

◦ Do no degrade readily

◦ Or, if they do degrade, break down into

compounds as dangerous or more dangerous

than the original pesticide

◦ Move around through the environment

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Pests and Pesticides

◦ BENEFITS OF PESTICIDES

◦ Disease control◦ Prevents illness transmitted by insects such as malaria (mosquitoes),

bubonic plague (rat fleas),

◦ Food and fiber production- increase food/fiber

supplies and lower food costs

◦ Efficiency in comparison Pesticides control most pests quickly and at a reasonable cost.◦ They have a long shelf life

◦ Easily shipped and applied

◦ Are safe when handled properly.

◦ When genetic resistance occurs, farmers can use stronger doses or switch to other pesticides.

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Pests and Pesticides◦ PROBLEMS WITH PESTICIDES:

◦ Many pest species evolve resistance

◦ Pesticides affect more than the target pests

◦ Pose threat to human health

◦ Persistence, bioaccumulation and biomagnification

◦ Readily move around the environment◦ The USDA says that only 2% of the insecticides from aerial

or ground spraying actually reaches the target pests

◦ Only 5% of herbicides applied to crops reaches the target weeds.

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Pests and Pesticides

◦First generation pesticides (pre 1940s

ish)◦ Inorganic compounds (lead, mercury, arsenic)

◦ Natural processes do not degrade

◦ Remain in the environment

◦ Organic compounds◦ Plant derived pesticides (botanicals)

◦ Do not persist in the environment

◦ Highly toxic to aquatic organisms and bees

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Pests and Pesticides

◦Second generation pesticides◦ Synthetic botanicals

◦ Human made, produced by chemically modifying the structure of natural botanicals.

◦ In the 1940s companies began to produce many synthetic organic pesticides

◦ DDT (dichlorodiphenyltrichloroethane) was the 1st

second generation pesticide

◦ Currently about 20,000 commercial pesticide products consist of about 675 active chemical ingredients

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Pests and Pesticides

◦ Three of the most important second

generation insecticides are◦ Chlorinated hydrocarbons

◦ DDT

◦ Broad spectrum, persistent, most banned in the U.S.

◦ Organophosphates

◦ Organic compounds, highly toxic, do not persist as long as

chlorinated hydrocarbons

◦ Used in large-scale operations like agriculture

◦ Carbamates

◦ Broad spectrum, generally not as toxic to mammals

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Toxins in the Environment

◦ Second generation pesticides:◦ Made wide spread from advances in

chemistry and production capacity during WWII

◦ Used for agriculture, lawns, golf courses,

to fight termites, ants……. Viewed as a

means towards a better quality of life

◦ 1962 Rachel Carson’s Silent Spring

brought the pesticide DDT (dichloro-

diphenyl-trichloroethane) to the

attention of the public

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Toxins in the Environment

◦ Silent Spring by Rachel Carson◦ The message- DDT in particular and artificial pesticides in

general were hazardous to people’s health and wildlife, and

the well-being of ecosystems

◦ By 1973 DDT became illegal in several nations and was banned

in the US

◦ Many developing countries still use DDT to control human

disease vectors such as mosquitoes that transmit malaria

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◦Carson pointed out that DDT, designed to kill

insects, was concentrated in these organisms

(insects) as they consumed chemical-laden

plants.

◦When songbirds ate the insects in large

quantities, they in turn accumulated large

concentrations of DDT in their bodies.◦ This inert chemical does not break down readily and the

body does not have an effective mechanism for excreting it.

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The birds would lay eggs that had a reduction in minerals (it prevents efficient calcium fixation) and the thin shelled eggs would break when the nesting birds sat on them for incubation.

Birds of prey such as hawks, eagles and falcons who ate the songbirds would accumulate even higher concentrations of DDT through biomagnification

The loss of young birds due to thin shelled eggs greatly diminished the songbird and predatory bird populations for a number of years, even after the use of DDT was banned in 1972

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Resistance

◦ Pesticide effectiveness declines with time as

pests evolve

◦ Pests typically have a short generation time,

have lots of offspring so they evolve quicker

than other species◦ K or R species?

◦ Pesticide treadmill◦ Creating stronger pesticides to combat pesticide

resistance

◦ Positive feedback loop

Toxins in the environment

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Resistance◦ 520 insect and mite species, 273 weed species, 150 plant diseases, and 10 rodent species (mostly rats) have developed genetic resistance to pesticides.

◦ At least 17 insect pest species are resistant to all major classes of insecticides

Toxins in the environment

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Affect Non Target Species

◦ Turning of minor pest into major pests.

◦ The natural predators, parasites, & competitors of

a pest may be killed by a pesticide it allows the

pest population to rebound.

◦ EX. DDT to control insect pests on lemon trees

caused an outbreak of a scale insect (a sucking

insect that attacks plants) that had not been a

problem.

Toxins in the environment

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Affect Non Target Species

◦ Each year pesticides:

◦ Kill about 1/5th of the U.S. honeybee colonies.

◦ 67 million birds.

◦ 6 -14 million fish.

◦ Threaten 1/5th of the U.S.’s endangered and

threatened species.

Toxins in the environment

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Pose Threat to Human Health

Short term and long term effects of pesticides Short term, high levels can harm organs and cause death Seen in farm workers, WHO estimates pesticides poison more than 4

million people each year

Long term, low levels over a long period of time can cause cancer Certain pesticides could disrupt the endocrine system

Seen in farm workers

A pesticide used on banana and pineapple plantations resulted in sterility in thousands of farm workers

Evidence shows pregnant women who live near pesticide applications have increased rates of miscarriages

Children of agricultural workers are at greater risk for birth defects

Toxins in the environment

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Persistence

◦ Some pesticides are extremely persistent in the

environment and maybe take many years to

break down into less toxic forms

◦ When persistent pesticides are ingested it is

typically stored in fatty tissue

◦ Over time, organisms may accumulate high

concentrations of the pesticide◦ This is called bioaccumulation

Toxins in the environment

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Persistence

◦ Organisms at higher levels in the food wed

tend to have greater concentrations of

pesticides stored in their bodies than those

lower in the food webs

◦ The pesticide passes through successive levels

of the food web◦ This is called biomagnification

Toxins in the environment

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Mobility in the Environment

◦Pesticides move through the soil, water

and air◦ Runoff can be lethal to fish and other aquatic organisms

◦ More than 14 million US residents drink water containing

traces of five widely used herbicides

Toxins in the environment

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Alternative Methods to Control Pests

◦ Cultivation Methods

◦ Biological Controls

◦ Pheromones and hormones

◦ Reproductive Controls

◦ Genetic Controls

◦ Quarantine

◦ IPM

◦ Irradiating food

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Cultivation Methods

◦ When agricultural practices are altered in which a way that a

pest is adversely affected or discouraged from causing damage

◦ Intercropping- alternating rows of different plants

◦ Corn and molasses grass

◦ Molasses grass repels some insects and attracts wasps that lay their

eggs inside other insects that destroy mature corn stalks

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Cultivation Methods

◦ Strip cropping- when one segment of the

crop is harvested at a time◦ The unharvested portion provides an undisturbed habitat

for natural predators and parasites of pest species

◦Proper timing◦ Planting, fertilizing and irrigating at an appropriate time

promotes healthy vigorous plants that are more resistant

to pests because they are not stressed by other

environmental factors

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Cultivation Methods

◦Crop rotation◦ When corn is not planted in the same field for two years

in a row the corn root worm is effectively controlled

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Biological Control

◦Biological control is a method of pest

control that involves the use of naturally

occurring disease organisms, parasites, or

predators to control pests◦ Bringing in an exclusive predator

◦ Care must be taken to ensure the introduce agent

doesn’t become a pest itself (Cane Toads!)

◦ Predators could be insects, nematodes, fungi, bacteria,

viruses

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◦ The common soil bacterium Bacillus thuringiensis (Bt) produces a

natural pesticide toxic to some insects

◦ When eaten by insect larvae, Bt toxin damages the intestinal

tract, killing the young insect

◦ Nonpesistant

◦ Not known to harm mammals, birds or other noninsect species

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Pheromones and Hormones

◦Pheromones- sexual attractants◦ Each species produces its on pheromone

◦ Pheromones can lure insects into traps or confuse insects so they cannot locate mate

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Reproductive Controls

◦ Sterile male technique◦ Large numbers of males are sterilized in a laboratory

using radiation of chemicals.

◦ One released they mate with females

◦ Eggs will never hatch

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Genetically Modified

◦ Plants can be genetically modified to produce toxin

or taste bad to predators.

◦ Bt toxin has been introduced into several plants such

as corn and cottonBoth tomato plants were exposed to destructive caterpillars. The

genetically altered plant (right) shows little damage.

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Quarantine

◦ Governments attempt to prevent the importation of foreign pests

and diseases by restriction of the importation of exotic plant and

animal material that might harbor pests

◦ If a foreign pest is detected on a farm the farmer may be

required to destroy the entire crop

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Integrated Pest Management

◦ Many pests are not controlled effectively with a single technique,

rather a combination of control methods

◦ Integrated Pest Management (IPM) combines a variety of

biological, cultivation and pesticide controls tailored to the

conditions and crops of an individual farm, campus, city, or green

house

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IPM◦ IPM allows the farmer to control

pests with a minimum of

environmental disturbance and

often at a minimal cost

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IPM

◦ To be effected IPM requires thorough

knowledge of the system including◦ life cycles

◦ feeding habits

◦ travel and nesting habits

…of the pests as well as all their interactions with their

hosts and host organisms

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IPM

◦Two fundamental premises:1. IPM is the management rather than the

eradication of pests Farmers tolerate low level of pests in their field and

accept a certain amount of economic damage

Do not spray pesticides at the first sign

2. Farmers need to be educated on IPM so

they know what strategies will work best

in their particular situation

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IPM

◦Popular in many parts of the world◦ Indonesia discovered by using pesticides alone they

were killing the natural enemies of the brown

planthopper which devastated rice fields

◦ In 1986 they banned the import of 57 pesticides and

promoted IPM

◦ Within 4 years they saved $179 annually by not

purchasing/subsidizing pesticides and rice yields rose 13%

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IPM

◦Many scientists urge the USDA to use three strategies to promote IPM in the U.S.:◦ Add a 2% sales tax on pesticides.

◦ Establish federally supported IPM demonstration project for farmers.

◦ Train USDA personnel and county farm agents in IPM.

◦ The pesticide industry opposes such measures.

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Irradiating Foods

◦ Harvested food can also be damaged by pests

◦ Food is then irradiated (exposed to ionizing radiation) to kill many

microorganisms such as salmonella

◦ Critics contend irradiation forms traces of certain chemicals

called free radicals (some of which are carcinogenic)

◦ We also don’t know the long term effects of eating irradiated

food

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Fig. 13-28, p. 295

Advantages Disadvantages

Save lives Promote genetic

resistanceIncrease food

supplies Kill natural pest enemies

Profitable to use Create new pest species

Work fast Pollute the environment

Safe if used

properly

Can harm wildlife and

people