Pests, Poisons and Pesticides

To maximize growth of the desired crop, we try to eliminate organisms that we consider pests. Pests are organisms that might compete or damage crop species. Agricultural pests are plants and animals that reduce crop yields.

For example, weeds are plants pests, mosquitoes are insect pests, and mice are rodent pests. The term pest is used only in reference to human wishes. There are no pests in nature.

All organisms are simply producers and consumers within food webs. By controlling pests, crops grow in the near-absence of their natural consumers and competitors.

For example, when a population of Colorado potato beetles finds a field of potatoes, they begin feeding and reproducing rapidly. Uncontrolled, the population could skyrocket and devastate the entire crop

There are many different kinds of pesticides… Herbicides (kills plant) Insecticides Fungicides Molluscicides (kills snails) Piscicides (kills fish)

Once applied, pesticides vary greatly in how long they persist or remain active in the environment.

Pesticides have helped farmers reduce crop damage from pests and increase food production. Pesticides have also helped control populations of biting insects, such as mosquitoes that spread disease.

Although benefits can result in more food and better health for some, pesticide use has a number of environmental and health costs. Pesticides become a potential source of pollution to the soil, air and water. They may also harm non-target species – species they were not intended to kill

Because broad-spectrum pesticides control many different pests, they may kill non-damaging and potentially beneficial organisms. They may kill species of predatory insects that might normally feed on pests. This creates a situation in which farmers become more dependent on pesticides.

One of the most serious side effects of pesticide use is their tendency to accumulate in individual organisms. The build-up of toxins in the body is referred to as bioaccumulation. All individuals are a part of a food chain. As a result, toxins stored in the fats of an organism at one trophic level are passed on to the organisms at the next trophic level. This is called bioamplification. This means that a pesticide, such as DDT, becomes more concentrated as you go up the food chain. Animals on top of the chain can have the highest concentrations of DDT.

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The benefit of pesticide use must be weighed against the risk of pollution, harm to non-target species, bioamplification and pesticide-resistance. One alternative option is using organic pesticides and fertilizers.

Organic farmers rely on a range of techniques: Biological control Predators feed on and infect prey species Ex wasps, ladybugs Altered timing Better timing of planting and harvesting can avoid peak pest populations

Crop Rotation & Mixing Plants Pest populations do not have the same opportunity to establish and prosper Baiting Pest Pheromone baits can be used to confuse some mating insects

Homework page 134 # 5, 6, 7 page 140 # 1-8