PESTICIDES Adapted from K. Sturges
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 (1/3 rd of that spent in the US)
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!
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
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.
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.
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
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 1 st second generation pesticide Currently about 20,000 commercial pesticide products consist of about 675 active chemical ingredients
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
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 (dichlorodiphenyl-trichloroethane) to the attention of the public
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
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.
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
Toxins in the environment 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 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 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 Affect Non Target Species Each year pesticides: Kill about 1/5 th of the U.S. honeybee colonies. 67 million birds. 6-14 million fish. Threaten 1/5 th of the U.S. s endangered and threatened species.
Toxins in the environment 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 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 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 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
Alternative Methods to Control Pests Cultivation Methods Biological Controls Pheromones and hormones Reproductive Controls Genetic Controls Quarantine IPM Irradiating food
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
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
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
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
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
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
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
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 cotton Both tomato plants were exposed to destructive caterpillars. The genetically altered plant (right) shows little damage.
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
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
IPM IPM allows the farmer to control pests with a minimum of environmental disturbance and often at a minimal cost
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
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
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%
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.
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
Advantages Save lives Increase food supplies Profitable to use Work fast Safe if used properly Disadvantages Promote genetic resistance Kill natural pest enemies Create new pest species Pollute the environment Can harm wildlife and people Fig. 13-28, p. 295