Growing Food: A Guide to Food Production

Transmission of Fungal Diseases
Fungi spread and multiply by means of spores, which are the fungal equivalent of seeds.
Their spores are dispersed in one of the following ways:

1. Soil-borne The spores fall off infected plants and are washed into the soil,


2. Wind-borne


3. Seed-borne


4. Insect-borne


5. Trash-borne

Fungicides
Fungicides are chemicals that will kill fungi and prevent the spread of disease, but they
should be applied in good time ie as early as possible.
Fungicides are used to control fungi that are spread either by the wind, in seed, soil
or trash, and by rain-splashes.
There are several different groups of fungicides, classified according to their
chemical structure and mode of action. They can be either CONTACT—acting at the
first point of contact with the plant, or SYSTEMIC—transported away from the point of
entry, to act elsewhere in the plant.
Successful fungicide programmes prevent and/or eradicate disease as appropriate.
Visible disease symptoms often develop some time after infection has occurred—this is

tible crop is grown the fungus enters the plants, produces more

spores, and so repeats the life cycle. Control is by crop rota-

can remain in the soil, viable, for many years. When a suscep-

tions, resistant varieties, seed dressing and the removal and

of cereals, Common Scab of Irish potatoes and Clubroot of

brassicas.

The spores are carried in the air, sometimes for thousands of

kilometres,until they land on susceptible plants, where they

develop. Control is mainly by growing resistant varieties, fun-

gicides and the destruction of infected plants - seed dressings

can control only a few, such as Ethirimol and Triadimenol for

destruction of infected plants. Examples: Take-all and Eyespot

the control of Powdery Mildew. Examples: Mildew and Rust

of cereals, Potato Blight of Irish potatoes and tomatoes, and

Chocolate Spot of beans.

The spores are carried either on the seed coat (exodermal

diseases), such as Bunt and Covered Smut of wheat, or inside

the seed (endodermal diseases), such as Loose Smut of wheat.

When the seed germinates and grows the fungus may either

and so cause the disease symptoms and produce more spores.

kill the seedling or it may develop together with the plant,

These fungi can normally be controlled with seed dressings.

Insects carry the spores from plant to plant, either within their

body or on the outside of it. This is a bigger problem with

virus diseases than with fungal diseases.

True Eyespot (Septoria) can be carried over in stems etc of

winter wheat, and Potato Blight can also be carried over on

potato haulm.

GROWING FOOD – THE FOOD PRODUCTION HANDBOOK 85

or they can enter the soil together with infected plants. They