Some Examples of Diseases caused by Viruses
- Irish potatoes are damaged by three viral diseases: Leaf Roll, caused by one
specific virus, Potato Mosaic, caused by various different viruses, and Spraing and
Mop Top, caused by soil-borne viruses. Control is mainly by using virus-free
“seed” ie tubers, which is grown in areas where virus diseases do not occur. If
symptoms do occur, the plants and tubers should be removed and destroyed as soon
as possible. - Mosaic and Virus Yellows are often found on sugar beet and mangels but rarely
cause significant damage. Control is mainly by controlling aphids, the only vector
of these diseases. - Cabbage Black Ringspot also attacks cauliflowers, turnips and Brussels sprouts. It
is spread by aphids, so control of aphids is the best control for this disease. - Cauliflower Mosaic. All volunteer plants and plants left in the field after harvest of
the brassica family should be removed and destroyed to prevent this and other
diseases. - Turnip Yellow Mosaic is spread by one of the flea beetles (Chrysomelidae), which
is unusual as this is a biting insect.
- Mosaic diseases of soybeans and several other crops.
C. Bacteria
Bacteria are essential to any ecosystem, because they are responsible for:
- the decomposition of organic matter built up by plants and animals;
- the production of essential nitrogenous plant nutrients;
- the reduction of cellulose-containing tissues to humus.
Unfortunately bacteria can also be very destructive (ie pathogenic), and cause diseases
in man such as typhoid, cholera, TB and diphtheria. In plants, bacteria cause diseases
when they become parasitic on those plants. Bacteria can multiply with fantastic speed,
by simple division of individuals into two halves.
Examples of Bacterial Diseases
Bacterial wilt of potatoes and tomatoes, Fire-blight of pears and apples, Blights and
Leaf Pustule of soybean, Blackleg of potatoes, Soft Rot of turnips and Crown Gall of
sugar beet.
Bacterial diseases are best controlled by the destruction of infected plants.
Bacteria and Legumes
The accumulation, or fixing (ie gas to solid), of nitrogen by the roots of legumes is
performed by a group of highly beneficial bacteria, and is discussed on page 54, 1Fe.
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and wheat with BaYMV (Barley Yellow Mosaic Virus), which is becoming a major
threat in Europe. Control of eelworms normally is crop rotation- Virus diseases (eg Lettuce Mosaic) are occasionally transmitted in or on the seed.
GROWING FOOD – THE FOOD PRODUCTION HANDBOOK
Groundnut Rosette Disease—described in Section 2B. “Legumes”, page 165.