Programme details: | Identify and Control Major Cassava Diseases on your Farm
Introduction.
Many plant diseases are caused by very tiny living things called pathogens. Pathogens are so tiny that you cannot see them even with a naked eye. Examples of pathogens are viruses, bacteria, and fungi. When a pathogen attacks a cassava plant, it multiplies and spreads inside or on the plant. As it spreads, it destroys the plant. The plant will show signs (symptoms) of attack.
Damage symptoms of major cassava diseases appear on the leaves, stems, and storage roots or tubers of the plant. Cassava diseases are recognized by their symptoms, such as discoloration of leaves, “sores” on the stems, and discoloration of storage roots.Some other diseases which you may notice in cassava are caused by non living things. Examples of such diseases are wilting due to drought and poor plant growth because of poor soils.
In this radio programme, we will highlight how to:
• Identify the major cassava diseases in Uganda, and
• Control these Diseases
MUSIC/SOUND EFFECTS.
Identifying the major cassava diseases in Uganda
The major diseases of cassava in Uganda are cassava Mosaic Disease, Cassava Brown Streak Disease (CBSD), and root rots. Some of these diseases attack the leaves and stems of cassava plants while others attack the storage roots.
Cassava Mosaic Disease is caused by a virus which occurs inside cassava leaves and stems. The leaves of cassava plants with the disease are discolored with patches of normal green color mixed with light green, yellow, and white areas. This discoloration is known as chlorosis. This makes it hard for the leaves to make food. When cassava mosaic attack is severe, the leaves are very small and distorted and the plants are stunted.
Control
The two main approaches to controlling CMD are through sanitation and the use of virus-resistant varieties and disease free planting materials. Use sanitation techniques, which involve taking cuttings only from healthy plants and subsequently removing any plants which become diseased. Plant disease free planting materials of two recommended varieties that have proved resistant to CMD which are 0067 (Akena) and 2961 (Variety with pink skin on tubers). After planting, any plants showing symptoms should be uprooted immediately. This rogueing should be carried out at least once a week for the first 2 to 3 months. ACMD symptoms are obvious from the onset and rogueing takes very little time. Whiteflies will not feed on wilted leaves; uprooted plants need not therefore be burnt but can be left on the surface to dry out. Control of whiteflies is not practicable under field conditions.
Cassava Brown Streak Disease is caused by a virus. Damage symptoms of the disease appear on the leaves, stems, and storage roots of cassava plants. On the leaves, the disease appears as patches of yellow areas mixed with normal green color. The yellow patches are more prominent on mature leaves than on young leaves. The damaged leaves do not become distorted in shape as occurs with leaves damaged by cassava mosaic disease. On the stems, the disease appears as dark brown “streaks” with dead spots on leaf scars. These streaks are most prominent on upper, green portions of the stems. The diseased plants may show shoot tip die-back. Cassava brown streak disease distorts the shape of the tubers and may cause cracks and discoloration in them.
Control
1. Farmers should destroy the infected plants including the roots. There is no problem of planting resistant varieties in the same field since the disease is not soil-borne.
2 - Two (2) recommended varieties that have proved resistant to CBSD are 0067 (Akena) and 2961 (Variety with pink skin on tubers). These varieties are also resistant to Cassava Mosaic.
3. - Farmers should select propagating material only from unaffected plants at the time they collect cuttings.
4. - Farmers in neighbouring fields should also destroy diseases plants
5- One management option is to harvest earlier as necrosis tends to affect roots of sensitive varieties from 5-6 months after planting. But early harvesting to avoid the effects of the disease still results in reduced yields because the crop is not in the field long enough to reach its full yield potential.
- Research is still on-going to produce a variety that is resistant to CBSD.
Cassava root rot diseases are caused by various kinds of fungi living on or in the soil. The fungi occur mainly in soils that do not drain properly and in forest fallow land that has been recently cleared. The leaves on cassava plants affected by root rot disease turn brown, wilt, and the plant appears scorched. The leaves may or may not remain attached to the plant, but the plant loses a lot of water and dies. If you suspect a cassava plant as having root rot disease, you should confirm this by uprooting it and examining the roots for the damage symptoms. Root rot diseases kill both feeder and storage roots of cassava. The storage roots may swell unusually and develop light brown coloration which you can see if the roots crack in the soil or if you cut them open. The roots may give out a bad smell as they rot.
Control
1. Select a site that is not prone to flooding or is not water logged at any part of the year. Avoid farming very close to rivers and streams that are likely to overflow their banks in the rainy season. It is common to find farmers who have limited access to land cultivating cassava in valleys that are subjected to flooding in good rainy days.
Roots of plants growing in water logged soils are not healthy and can easily be attacked by diseases. A sandy loamy soil that is well drained is a good soil type for cassava.
2. Do not cultivate cassava on land that has a history of root rots and other major diseases. This information can be obtained from neighbours farming close to the land. If the only available land has a history of rots, then good disease management practices must be maintained if good yields are expected.
3. Use disease resistant or tolerant varieties. Improved cassava varieties with resistance or tolerance to certain important diseases and pests (that are also high yielding) have been developed and released by a number of Agricultural Institutions. It is therefore important to report any disease situation that is affecting your yields to Agricultural Extension Agents who operate in your communities. Ask questions on the availability of resistant materials and how to obtain them. It is always advisable to start your farm with disease resistant varieties if they are available. This helps you among other things to obtain higher crop yields.
4. Avoid using planting materials from fields with visible signs of root rot diseases even if the stems look healthy. The structures of disease causing fungi that give rise to new attacks or infections called spores are microscopic and planting materials from farms with visible root rot attacks are likely to carry several of these spores to new farms.
5. Practise good farm sanitation. This means that you collect plant debris (stems and roots) with fungi together and burn to destroy particularly after harvest. Rotten roots and plant debris bearing fruiting bodies of disease causing fungi must be destroyed by burning to reduce the spread of root rot diseases. Disease severity on farms can be reduced through destruction of debris that carry spores into the next planting season.
6. Regularly inspect the field to remove and destroy the plants showing disease symptoms such as patches of fungal growths, wilting and defoliation (that may be symptoms of root rot and other diseases) by burning reduce spread of diseases on farms. This practice called roguing can be an effective disease management strategy if regular inspections are well planned and followed.
It is also important for farmers to use cuttings from healthy plants. Choose cuttings that have no cuts or bruises. Take cuttings from mature plants that have fully grown tubers and are at least 8 to 10 months old. Take cuttings that come from the bottom and middle parts of the stem. Make cuttings that are 20 to 30 centimetres long, at least 2 centimetres thick and have 5 to 7 nodes.
In Summary
To control diseases and grow a healthy cassava crops, farmers need to:
• Identify the common cassava diseases, their damage symptoms, and know the conditions under which they will cause severe losses.
• Select sites with dense vegetation, deep loamy soils, and flat or gently sloping land to grow cassava.
• Improve the soils by manuring, mulching, and intercropping to encourage cassava plants to grow vigorously and offset damage by cassava diseases.
• Grow cassava varieties that tolerate the common cassava diseases in your area.
• Plant stem cuttings from healthy plants without leaf chlorosis, shoot tip die-back, cankers, fungus patches, or streaks on the stems.
• After root harvest destroy discarded cassava stems and storage roots showing any symptom of disease.
• In the control of cassava mosaic disease, select planting material mainly from stem branches; avoid the basal and main stem portions as sources of stem cuttings.
• Plant cassava mainly at the beginning of the wet season; try and avoid late planting. |
Information sources: | 4861, 5149, 5139, 5288, 5506, 5511, 4874, 5037, 4836 & 5326 |
Uganda
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