R2103 June ‘19
Describe what is meant by plant disease. 2 marks
Describe honey fungus under EACH of the following headings:
Damage caused 2 marks
ONE method of spread 2 marks
TWO distinct methods of control 4 marks
This question relates to the following part of the syllabus:
Outcome 4. Understand the problems caused by diseases and methods by which they can be minimised.
4.1 Explain why plant diseases need to be controlled. State what is meant by the term ‘plant disease’. Describe the damage caused by plant diseases to include: - grey mould - strawberry powdery mildew - damping off - honey fungus - rose black spot – potato blight - club root - hollyhock rust - apple and pear canker - fireblight - bacteria canker on Prunus - potato leaf curl virus (and vector peach potato aphid) - tobacco mosaic virus blight
4.3 Describe the biology of diseases. Describe methods of spread of EACH of the diseases named in 4.1
4.4 Describe how diseases can be controlled. Describe TWO different methods of minimising the effects (including prevention) of EACH of the diseases stated in 4.1. Methods to be selected from more than one of the control options (physical, cultural, or chemical) available. Describe TWO methods of avoiding the spread of plant viruses. Explain how knowledge of the life-cycle and biology of diseases stated in 4.2 contribute to the success of their control.
The first part of the question is a general introduction and part b) goes on to ask about one specific disease. There is a list of thirteen different diseases that you need to learn about specifically for this unit. For these you need to know the damage caused, methods of spread and two methods of preventing or controlling them. There are sometimes questions that focus on one particular plant disease as with this one, or you may need to demonstrate knowledge of several different diseases in others.
For part a) the examiners’ comments suggest a correct description as ‘an abnormal growth and/or dysfunction of a plant caused by an infectious micro-organism (pathogen) e.g. virus, bacteria, fungi. There are obviously different ways of phrasing this, but you need to get across the two main points here for the two marks.
Always make sure you look at the allocation of marks for each part. The first two parts for b) are worth 2 marks each, but the third part has 4 marks allocated so needs more included.
For the damage caused, the examiners’ comments suggest the following:
The crown of the tree sometimes dies suddenly during periods of hot, dry weather indicating a failure of the root system. The leaves are smaller and paler than average. The tree may fail to flower or produce a large number of flowers followed by a heavy crop before it dies. Cracking and bleeding of the bark at the base of the tree and dead or decaying roots may be present.
Not all of this would be needed for full marks.
For the method of spread, the examiners’ comments suggest:
Honey fungus is spread via rhizomorphs underground and can spread up to 30m in the top 15cm of the soil. It can also spread through direct contact of the roots of affected trees with unaffected ones.
Two methods of control are needed, so use bullet points or numbers to indicate the two points clearly. The examiners’ comments suggest the following:
Plant species that show some resistance to honey fungus e.g. Ginkgo biloba, Quercus ilex and do not plant susceptible species e.g. Fagus sylvatica, Ligustrum vulgare. Dig out the whole tree including the stump and as much root as possible and destroy it by burning. A trench can be dug around the affected tree and a butyl rubber sheet used to form a barrier to prevent the growth of the rhizomorphs.