Pesticides

Question 1

Herbicides

Answer 1

Kill weeds

Question 2

Pesticides

Answer 2

Chemical means to control weeds, pests and diseases.

Question 3

Fungicides

Answer 3

Control fungal diseases

Question 4

Insecticides

Answer 4

Kill insect pests

Question 5

Molluscicides

Answer 5

Kill mollusc pests

Question 6

Nematicides

Answer 6

Kill nematode pests

Question 7

Herbicide categories

Answer 7

Selective, systematic and contact

Question 8

Selective herbicides

Answer 8

Stimulate growth until the broad-leaved weed exhausts its food reserves and dies. Similar properties to plant hormones. Example - PREEN

Question 9

Contact herbicides

Answer 9

Non-selective and short-lived. Perennials with

storage organs not affected. Example - RESOLVA

Question 10

Systematic herbicides

Answer 10

Absorbed by the weed then spreads through the vascular system of the plant. Very effective, but may take time to act. Will destroy the whole plant and regrowth/regeneration prevented.
Example - ROUNDUP

Question 11

Systematic insecticides

Answer 11

Systemic insecticides, molluscicides and nematicides are absorbed by the plant and transported in the phloem to all of its parts. This kills pests feeding on the plant

Question 12

Diseases forecasts

Answer 12

Where invasion of a plant by a pathogen requires a narrow range of environmental conditions, preventative action can be taken.
Conditions can be monitored and growers alerted to periods when chemicals, such as fungicides, should be applied.

Question 13

Protective applications of fungicides

Answer 13

Protective applications of fungicide based on disease forecasts are often more effective than treating a
diseased crop.
When to apply the fungicides is determined by the disease forecasts

Question 14

Problems with plant protection chemicals

Answer 14

• Toxicity to non-target species;
• Persistence in the environment;
• Accumulation or magnification in food chains;
• Production of resistant pest populations.

Question 15

Toxicity to non target species

Answer 15

Some pesticides are poisonous not only to the intended species but to a broader range of animals, including humans
Example dieldrin used to eradicate beetles, however humans ingested it and linked to human health problems

Question 16

Persistence in the environment

Answer 16

Some protective chemicals may be persistent – this means they do not biodegrade and will remain in the environment for a long period of time.
DDT killed top predators in food chains

Question 17

Bioaccumulation

Answer 17

Accumulation of chemicals can occur
(particularly when they are persistent) if an organism absorbs the chemical at a faster rate than it is lost. This can mean the chemical becomes toxic in the organism due to the build up.

Question 18

Biomagnification

Answer 18

Some chemicals can also be magnified along the food chain. This results from the chemical concentration increasing from one trophic level to the next.

Question 19

Production of resistant population

Answer 19

When pesticide is applied to a crop a few members among the pest population many already be resistant to the chemical due to random mutation. This feature is now of selective advantage to them given the selection pressure of the pesticide. This advantage could be the possession of a thick coat or the ability to produce an enzyme that breaks down the toxin.