3.3 Crop Protection

Question 1

how do weeds reduce the productivity of a crop?

Answer 1

by competition

Question 2

what resources plants compete for?

Answer 2

• water
• sunlight
• root space
• soil nutrients

Question 3

how can weeds reduce the economic value of a crop?

Answer 3

• weeds can release chemicals which reduces the germination of crop seeds
• some weeds can act as vectors for disease
• weed seeds can contaminate the harvested crop

Question 4

describe ‘annual types of weeds’

Answer 4

• the plant germinates, grows, flowers (and produces seeds in one year), then dies
• rapid growth
• short life cycle
• high seed output
• seeds can remain dormant for years

e.g. chickweed

Question 5

describe ‘perennial types of weeds’

Answer 5

• the plant survives over many years
• has storage organs, which allow them to survive in adverse conditions
• often use vegetative propagation to spread

e.g. dandelion

Question 6

describe ‘nematode worms, molluscs and insect’s adaptations that make them a pest to crops’

Answer 6

Nematode Worms
- e.g. eel worms
- tiny worms which are often parasitic

Molluscs
- e.g. slugs and snails
- they have rasping mouthparts which can cause massive leaf damage

Insects
- e.g. greenflys and caterpillars
- greenfly pierce plant tissue and suck up the sugary liquid from the phloem
- caterpillars eat vasts amounts of green leaf material

Question 7

explain ‘why the leaf damage, caused by slugs and snails, decreases the productivity of a crop plant (such as a potato)’

Answer 7

less leaf area means less photosynthesis occurring, and less sugar produced by the plant to be stored as starch, leading to smaller potatoes and a decrease in productivity

Question 8

plant disease can be caused by b…, f… or v…

Answer 8

• bacteria
• fungi
• virus

Question 9

describe ‘the crop disease, black rot’

Answer 9

• caused by bacteria
• affect brassicas (e.g. cabbage, broccoli and spouts)
• it gives the plant lesions, vascular blackening, wilting, a stunted growth and stem rot symptoms reducing productivity

Question 10

what name is given to an organism that transfers a disease from one host organism to another?

Answer 10

a vector

Question 11

explain ‘how ploughing, weeding and crop rotation help to increase crop yield’

Answer 11

Ploughing
- buries many of the perennial weed to a depth of which they die and decompose

Weeding
- removes plans which could reduce the germination or inhibit the growth of crop plants when they are young and vulnerable

Crop Rotation
- a 4-year rotation in any one field (such as barley, potatoes and turnips) will allow nutrient levels to recover and pest numbers to be kept in check

Question 12

name the 5 main pesticides

Answer 12

• insecticides
• molluscicides
• herbicides
• nematicides
• fungicides

Question 13

describe ‘selective herbicides’

Answer 13

• have a greater effect on certain plant species, than they do on others
• they work by mimicking plant growth hormones, causing uncontrolled growth in the weed, to the extent that the weeds exhaust their food supply and die
• work best on broad-leaved plants and have little effect on crop plants

Question 14

describe ‘contact herbicides’

Answer 14

• destroy all plants that they come into contact with
• they are biodegradable, so their effects are short lived and they do not affect underground storage organs
• perennial weeds with established underground storage organs can re-emerge in the future

Question 15

describe ‘systemic herbicides’

Answer 15

• slower to act on other herbicides, but more effective on perennial weeds in the long run
• the chemical enters the weeds circulatory system and is transported to all parts of the weed, killing underground roots and storage organs, as well as the surface plant

Question 16

describe ‘fungicides’

Answer 16

fungicides are sprayed onto crops, killing fungal spore when they land on the crop plant and begin to germinate

Question 17

explain ‘why the use of the insecticide, DDT, is banned in Europe and the US’

Answer 17

DDT is an insecticide which was used widely in the 1950’s and 1960’s. It was extremely effective because it didn’t biodegrade. It persisted in the environment, and through bioaccumulation, built up in the fat tissue of birds and animal, and by biomagnification, became concentrated in by food chains.

The raid decrease in the numbers of song birds and birds of prey was proved to be caused by DDT, and its toxicity to non-target species.

Question 18

describe ‘how it is possible for some insect population to become resistant to a pesticide’

Answer 18

individual insects with a mutation that confers resistance to the pesticide, survive to reproduce, passing on the gene to their offspring, causing an increase in the frequency of pesticide resistance in the population

Question 19

biological control involves the introduction of a biological agent, which could be a p…, a p… or a p… of the pest

Answer 19

• predator
• parasite
• pathogen

Question 20

give an example of successful biological control

Answer 20

• using ladybirds to control greenfly populations in polytunnels
• myxomatosis virus controlling rabbit populations in the UK

Question 21

what negative effects on biodiversity could control organisms have?

Answer 21

• may become an invasive species
• may parasite other non-pest species
• may become a predator of other non-pest species
• may become a pathogen of other non-pest species

Question 22

integrated pest management is the combination of chemical, biological and cultural control

the aim is usually the control of a pest species rather than its eradication, why is this?

Answer 22

Pest species are often only a problem in large numbers, and can be vital food sources for other non-pest species in the ecosystem. Therefore, the aim is usually to control a pest species instead of completely eradicating them, as this may have unpredictable results on the biodiversity of an area.