Chemical and Biological Pest control

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What is a pest and how can we control them?

Agricultural ecosystems attempt to channel as much of the Sun's availible energy into the human food chain directly. However, we must also be aware that food chains are part of complex food webs, so there will be other organisms competing for the same food sources as us. These are pests.

Pest: An organism living or growing where we do not want it.

We can control pests in two main ways:

-Chemical pest control

-Biological pest control

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Chemical pest control (Pesticides)

Pesticides are poisonous chemicals that kill pests.

To be effective, a pesticide should:

- Be specific: It should only be toxic to the organism it is intended to kill, so it's not harmful to humans, natural predators of the pest, earthworms, pollinating insects (bees) and just general everything else.

- Biodegrade: So it will break down into chemically harmless substances/molecules. However, it must also be chemically stable to have a long shelf-life.

- Cost-effective: It is v expensive to produce pesticides and pests can quickly develop genetic resistence to pesticides, rendering them ineffective.

- Not accumulate: It should not accumulate as it goes down the food chain or in a particular organism.

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Biological pest control

The biological control method aims to control pests through natural predators or parasites of the pests.

This method looks to control the pest population and not kill it because if that happens, then the pest population will decrease, then the population of the predators will die and the population of the pest will be allowed to rise unchecked.

Therefore, the levels of control organism and pest must exist in balance where the pest has little or no effect.

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Comparison of the two methods


+ Very Specific

+ Once introduced, the control organism reproduces itself.

+ Pests don't become resistant

- Don't act quickly (some time interval)

- The control may become a pest - if the population increases and it turns to the crops as an alternative source of food.


- Always has some effect on non-target species.

- Must be reapplied at intervals making it expensive.

- Pests can develop genetic resistance.

+ Effective immediately.

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Integrated Pest control

A better way to control pests is by integrating all methods of pest control to focus on reaching an acceptable pest level.

This involves:

- Choosing local plant + animal varietes that are as pest resistant as possible.

- Managing the environment to provide suitable habitats for predators close to the crops.

- Regularly monitoring crops for signs of pests - early detection helps.

- Removing pests mechanically if level exceeds acceptable. (e.g. handpick)

- Using biological agents if necessary and availiable.

-Using pesticide as a last resort.

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How do pests affect productivity?

1) Pests reduce productivity

e.g. weeds compete with crops for light, water, minerals etc, so they are limited for crops. One may also become a limiting factor, so photosynthesis is reduced = >productivity.

2) Insects may damage crop leaves so > photosynthesis and may even eat the crop itself.

3) Many crops are grown in monoculture, which makes it easier for insects and fungal pests to spread.

4) Pests can also affect animals; they may not grow properly, be fit to eat, or die, which therefore decreases productivity.

Pest control tries to balance costs with benefits. (e.g. cheap food v conservation)

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