Symptoms of disease and physiological disorders

Below in Table 15.2 is a summary of the most important symptoms to help the reader 'home-in' on disease problems and physiological disorders.

Table 15.2 Some symptoms of diseases and physiological disorders

Symptom

Cause

Other cause

Leaf spot

fungus e.g. apple scab

bacterial canker (Prunus)

Raised leaf spots

rusts

oedema (corky spots)

White covering on leaf

powdery mildew - upper

spraying hard water

downy mildew - lower

Leaf yellowing

1 ow nitrogen levels

root disease

Brown edge to the leaf

l ow potassium

Leaves curl and go brown

underwatering

Dry, crumbling leaves

plants overheated

too much fertilizer

Yellow leaf veins

1 ow magnesium/iron

Dark coloured leaves

l ow phosphorus

Lower leaves yellow

wilt fungus

overwatering

Yellow/ green leaf mottle

virus mosaic

mutation/chimaera

Fruit spots

fungus

bitter pit (apple)

Sunken fruit lesions

blossom end rot (tomatoes)

Bud or leaf drop

sudden change of temperature

Stems elongated

too little light

Whole plant wilts

severe underwatering

wilt disease, vine weevil grubs

Fluffy mould

Botrytis (grey)

Penicillium (blue)

Brown stem lesions

tomato mosaic virus

Swollen woody stems

fungal/bacterial canker

Oozing from woody stems

bacterial canker/fireblight

Brown roots

root rot

overfertilizing

Check your learning

  1. Define the term 'disease'.
  2. State the damage caused by three named fungal diseases.
  3. Describe the life cycle of one named fungal disease.
  4. Describe how the life cycle in the above fungal example is related to its control.
  5. Describe the available control measures for the disease in question 3.
  6. State the damage caused by one named bacterial disease.
  7. Describe one method of reducing the damage caused by the above-named bacterium.
  8. Explain how fungal resistance to fungicides can be reduced.
  9. Explain the difference in the symptoms caused by downy mildews and powdery mildews.
  10. Explain what disease danger the roots of a dead tree represent to plants in its vicinity.

Further reading

Agrios, E.N. (2005). Plant Pathology. Academic Press.

Brown, L.V. (2008). Applied Principles ofHorticultural Science. 3rd edn.

B utterworth-Heinemann. Buczacki, S. and Harris, K. (1998). Guide to Pests, Diseases andDisorders of

Garden Plants. Collins. Cooper, J.I. (1979). Virus Diseases ofTrees andShrubs. Institute of Terrestrial Ecology.

Fletcher, J.T. (1984). Diseases ofGreenhouse Plants. Longman. Greenwood, P. and Halstead, A. (2007). Pests andDiseases. Dorling Kindersley. Hope , F. ( 1990 ). Turf Culture: A Manual for Groundsmen. Cassell . Ingram, D.S. et al. (eds) (2002). Science and the Garden. Blackwell Science Ltd. Lindow, E.S. et al. (2002). Phyllosphere Microbiology. American Phytopathological Society.

Scopes, N. and Stables, L. (1989). Pest andDisease Control Handbook. British Crop

Protection Council . Snowdon, A.L. (1991). Post-harvest Diseases andDisorders ofFruits and

Vegetables. Wolfe Scientific. UK Pesticide Guide (2007). CAB Publishing.

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