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William P. CunninghamUniversity of Minnesota

Mary Ann CunninghamVassar College

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Chapter 10Chapter 10

Lecture OutlineLecture Outline**

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Pest Control

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Outline

• Pests• Pesticides

Types Benefits Problems Alternatives Reducing Exposure Regulating Use

• Organic Farming

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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

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Pesticides

• Pesticide - chemical that kills pests Biocide - kills wide range of organisms Herbicide - kills plants Insecticide - kills insects Fungicide - kills fungi Acaricide - kills mites, ticks, and spiders Nematicide - kills nematodes Rodenticide - kills rodents Avicide - kills birds

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Conventional Pesticide Use

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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.

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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.

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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.

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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

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Use of Pesticides in the U.S.

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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.

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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

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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.

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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.

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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.

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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.

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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

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Environmental Persistence and Mobility

• Many persistent organic pollutants were banned globally in 2001. 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.

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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?

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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

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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

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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

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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

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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.

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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.

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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.

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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.

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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.

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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.