Controlling the spread of plant disease

Plant pathogens cause diseases with a range of different symptoms. These symptoms can be used to identify the pathogen and then treat the disease, or limit its effects.

The symptoms of rose black spot and the tobacco mosaic virus (TMV) are shown below.

A leaf infected with rose black fungus

Symptom and example of disease

Spots on leaves caused by the rose black spot fungus

Controlling the spread of tobacco mosaic virus

To control the spread of TMV, farmers must:

  • dig up and destroy infected plants
  • wash their hands after handling infected plants
  • wash tools that have come into contact with infected plants in detergent or bleach
  • rotate the crops they grow in a contaminated field - they must not grow tobacco or tomato plants in the field for at least two years

Plant scientists have now also produced varieties of crops - by selective breeding and genetic engineering - that are resistant to TMV.

Controlling and treating rose black spot

Black spot is treatable using fungicides. The fungicide can also be sprayed on rose bushes to prevent infection, especially when the weather is likely to be warm and wet.

Transmission can be reduced by:

  • not planting rose bushes too close together, which allows air to circulate around the plants
  • avoiding wetting the leaves when watering the plant
  • collecting and destroying infected leaves

Many rose growers also now grow resistant varieties of roses.

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