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Another exam question commentary - Level 2 Protected Cropping
by Janet Prescott - Tuesday, 28 April 2020, 12:53 PM

From R2114 Feb 2019


a)      Describe ONE NAMED biological method of pest control in a protected structure.              

4 marks

b)     Describe THREE reasons why this method of control is particularly important.

6 marks

This question relates to the following part of the syllabus:

Outcome 4.  Understand the control of the environment in protected structures.

4.6 Describe the importance of cultural and biological controls to limit the damage caused by plant pests and diseases. 

State what is meant by cultural and biological controls;  Describe the use of cultural controls to limit two pests or diseases. Give two examples of how biological controls are used for specific pests (Latin names for biological controls are not required: type of control - nematode, mite, wasp, ladybird – is sufficient with the correctly identified pest.) State the advantages that cultural and biological control have over chemical control methods.

Part a) - the syllabus requires you to know two examples of biological controls and just one is needed here. Think about how much you know about the biological control before you choose which one to describe. Make sure it is one that is suitable for a protected structure as well. As the question asks you to ‘describe’ make sure you include a good amount of detail.

The examiners’ comments state that most candidates described Encarsia formosa for the control of Glasshouse Whitefly. According to the syllabus you don’t need the Latin name, but if you do know it is much easier to use it. Otherwise just state that Glasshouse Whitefly can be controlled by a parasitic wasp. The detail suggested for the description includes how this parasitic wasp lays its eggs in the immobile whitefly scales. Within 10 days the whitefly scales turn black. Encarsia formosa is usually supplied as parisitised whitefly scales containing the pupal stage of the parasitic wasp on carrier cards. These are placed on the infected crops as soon as the pest is present.

Part b) – this part also needs a lot of detail as it is ‘describe’ and is worth 6 marks. However, as three reasons are required, this helps with the amount of detail needed. The numbers are always in bold which makes it easier to pick out. You won’t get any more marks for writing about more than the stated number.

The examiners’ comments suggest the following as suitable answers:

·        Pesticides are not used and it is therefore more environmentally friendly as biological control does not enter the water supply.

·        As no pesticides are used there is no clearance period which must be adhered to before harvesting and there is no build-up of chemicals on edible crops.

·        As no pesticides are used there is no opportunity for the pest to build-up a resistance to the control method.

·        There is no likelihood for the operator being poisoned if pesticides are not used and less training is required when using biological control.

·        As no chemicals are used there is no requirement to store and transport chemicals and adhere to Health and Safety regulations and no need for additional protective clothing.