4 Pests and Pesticides Biological Pests - organisms that reduce the availability, quality, or value of resources useful to humans Only about 100 species of organisms cause 90% of crop damage worldwide. - Insects are most frequent pests. Make up three-fourths of all species Generalists Compete effectively against specialized endemic species
7 Early Pest Controls Sumerians controlled insects with sulfur 5,000 years ago. Chinese describe mercury and arsenic to control pests 2,500 years ago. People have used organic compounds and biological controls for a long time. Romans burned fields and rotated crops to reduce crop disease.
8 DDT Era of synthetic organic pesticides began in 1939 with DDT. Inexpensive, stable, easily applied, highly effective By 1960’s, evidence of concentration through food chains. Carnivorous birds such as eagles suffered egg shell thinning leading to an inability to reproduce. In 1962, Rachel Carson published Silent Spring warning of the dangers.
9 DDT Banned in developed countries by late 1960’s; still used in developing countries Most prevalent contaminant on U.S. imported food The example of DDT highlights a more general problem with synthetic pesticides. Many of them have proven to have unintended consequences on non-target species.
10 Current Pesticide Use EPA estimates total pesticide use in the U.S. amounts to about 5.3 billion pounds annually. Roughly half is chlorine and hypochlorites used for water purification Roughly 80% of all conventional pesticides applied in the U.S. are used in agriculture or food storage and shipping. Remainder are used as preservatives in wood, leather and other materials
11 Use of Pesticides in the U.S.
12 Pesticide Types Inorganic Pesticides – broad-spectrum, generally highly toxic, and essentially indestructible (arsenic, copper) Generally neurotoxins Natural Organic Pesticides - generally plant extracts (nicotine, pyrethrum, turpentine) Fumigants - small molecules that gasify easily and penetrate materials rapidly (carbon tetrachloride, ethylene dibromide). Extremely dangerous; many have been banned.
13 Pesticide Types Chlorinated Hydrocarbons - fast acting and highly toxic to sensitive organisms (DDT, mothballs) Inhibit nerve membrane ion transport and block nerve signal transmission Persistent and concentrated in food chain Organophosphates - extremely toxic to mammals, birds and fish (Malathion) Inhibit cholinesterase, an enzyme necessary for nervous system function A single drop can be lethal, so dangerous to workers Quickly degraded
14 Pesticide Types Carbamates - similar to organophosphates (Sevin) - Extremely toxic to bees Halogenated pyrroles - new class of compounds based on a microbial toxin. Marketed as “Pirate.” Shown to reduce duck reproduction. Biological Controls and Microbial Agents - living organisms or toxins derived from them are used in place of pesticides Bacteria such as Bacillus thuringiensis kill beetles. Parasitic wasps such as Trichogramma kill moths.
15 Pesticide Benefits Disease Control Many insects serve as disease vectors. - Anopheles mosquito spreads malaria. Crop Protection Using pesticides, pre-harvest losses to diseases and pests are at 33%, with post-harvest losses at an additional 20-30%. Losses would be much higher without pesticides. In general, farmers save an average of $3-$5 for every $1 spent on pesticides.
16 Pesticide Problems Non-Target Species Up to 90% of pesticides never reach intended target and many beneficial organisms are killed. Pesticide Resistance and Pest Resurgence Resistant members of a population survive pesticide treatment and produce more resistant offspring. - Pest Resurgence Pesticide Treadmill - as pests become resistant, we must develop new pesticides.
17 Creation of New Pests Broadcast spraying is also likely to kill beneficial predators. Under normal conditions many herbivorous pests are controlled by natural predators. When we kill the predators, we release the pests from their natural controls. With advent of chemical pest controls, farmers have tended to abandon traditional methods of pest/pathogen control such as crop rotation.
18 Environmental Persistence and Mobility Because chlorinated hydrocarbons (DDT) are so persistent, they tend to show up far from the point of dispersal. Stored in fat and tend to bioaccumulate - High levels detected in upper levels of food chain - Accumulate in polar regions due to the “grasshopper effect”. Evaporate from warm regions, condense in cold regions
19 Environmental Persistence and Mobility Many persistent organic pollutants were banned globally in Use was previously banned or restricted in developed countries, but U.S. companies continued to sell POPs in underdeveloped countries where regulations were lax. - Many pesticides then returned to U.S. in agricultural products and migrating wildlife. Since the treaty banning POPs, other pesticides have taken their place.
20 Human Health Problems WHO estimates 25 million people suffer pesticide poisoning, and 20,000 die each year. At least 2/3 of these result from occupational hazards in developing countries. Long-term health effects difficult to conclusively document. - PCBs in Great Lakes fish have been linked to learning deficiencies in children whose mothers ate the fish. - Children whose homes are fumigated are 3X more likely to get acute lymphocytic leukemia. - Is autism linked to environmental toxins?
22 Alternatives to Pesticide Use Behavioral Changes Crop Rotation Mechanical Cultivation Flooding Fields Habitat Diversification Growing in Pest-Free Zones Adjusting Planting Times Plant Mixed Polycultures Tillage at the Right Time
23 Biological Controls Predators or pathogens Insects that eat weeds Plants like the neem tree that make their own pesticides Bioengineering Release of sterile male insects Hormones that disrupt development or attract insects to traps
24 Integrated Pest Management Flexible, ecologically-based strategy that uses a combination of techniques applied at specific times aimed at specific pests Tries to minimize use of chemical controls and avoids broad spectrum controls Uses preventative practices to encourage beneficial organisms and enhance plant defenses Employs economic thresholds to determine the point at which potential economic damage justifies pest control expenditures
25 Integrated Pest Management Time, type and method of application are critical Trap crops - small areas planted before the main crop. These plants mature first and attract the insects, and the trap crop is then sprayed heavily to destroy them. Crop is cut down and not sold. IPM is being used successfully all over the world. Cuts pesticide use while maintaining yield. But must be careful that introduced organisms do not become pests themselves
26 Reducing Pesticide Exposure Less than 10% of active pesticide ingredients have been subjected to a full battery of chronic health- effect tests. Of the 321 pesticides screened, EPA reports 146 are probable human carcinogens. - Since 1972, only 40 pesticides have been banned.
27 Regulating Pesticides Environmental Protection Agency (EPA), Food and Drug Administration (FDA) and Department of Agriculture (USDA) all share federal responsibility for regulating pesticides used in food production in the U.S. EPA regulates sale and use, and sets tolerance levels. FDA and USDA enforce pesticide use and tolerance levels set by EPA.
28 Regulating Pesticides In 1996, Congress passed Food Quality Protection Act requiring the EPA to set aggregate exposure limits and examine inert ingredients in pesticides. Based on the new rules, EPA banned use of methyl parathion on all fruits and many vegetables and prohibited use of Dursban. Studies show children are more susceptible than adults to toxic pesticides. Ban of CCA treated lumber (chromated copper arsenate) used in play equipment and decks.
29 Regulating Pesticides 38% of fruits and 12% of U.S. vegetables are imported. Less than 0.2% is inspected for pesticides, which are widely used in developing nations.
30 Is Organic the Answer? Numerous studies have shown organic, sustainable agriculture is more eco-friendly and leaves soil healthier than intensive, chemical-based mono- culture cropping. Currently, less than 1% of all American farmland is organic but market is growing. Organic food must be produced without the use of hormones, antibiotics, pesticides, synthetic fertilizers or genetic modification. Animals must be raised on organic feed, given access to the outdoors, given no steroids or growth hormones and given antibiotics only to treat disease.
31 Is Organic the Answer? Critics are disappointed by limited scope of the definition of organic. They hope to include: Growing food in harmony with nature Food distribution based on co-ops, farmer’s markets, and local production Food should be simple, wholesome, nutritious. At present, processed ingredients are allowed in organic food. Some doubt whether organic growers can produce enough to feed everyone.