Keep diseases away from your cassava crop

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Cassava farmers suffer huge losses due to outbreak of diseases. Proper selection of planting material and good management can prevent common diseases and increase crop yields. Studies have shown that the best way to control diseases is to grow a healthy crop of cassava.

Cassava farmers in Nyanza and Western regions in Kenya are experiencing challenges in controlling diseases that seriously affect the crop in their farms resulting in low yields. The worst hit regions include; Busia, Teso, Bungoma, Siaya, Bondo, Rachuonyo, Homabay, Megara and Kuria, which for a long time have been known to be the best producers of cassava. The effect has been such great that some farmers have replaced the crop with others such as maize, millet and potatoes. To evade disease, some farmers have planted and consumed varieties that are not suitable for human use.

How to prevent cassava diseases

- Grow healthy cassava seedlings

Studies have shown that the best way to control diseases is to grow a healthy crop of cassava. This is especially so because you do not see the viruses, bacteria and fungi which cause diseases. In order to grow a healthy crop you will need to combine plant production and plant protection practices in growing the crop. These include practices as show below:

- Use IPM methods

Integrated Pest Management (IPM) practices for control of cassava diseases can be used at planting. These include proper site selection, soil improvement practices, and selection of appropriate varieties and planting materials. Scientists and extension agents confirm that some cassava varieties can withstand disease attack better than others. In selecting a variety to grow against diseases you should find out if the selected variety has other features you desire.

- Get good planting material

Almost all cassava diseases are spread by planting infected stem cuttings. The viruses, bacteria and fungi, which cause various diseases survive on or inside cassava stems and are easily carried to new fields in this way.

In selecting planting material, you should avoid cassava plants which show leaf discolouration or chlorosis, leaf blighting and wilting, gum exudates, cankers, fungus or patches and streaks on the stems and defoliation, shoot or shoot tip die-back. Stem cuttings from such plants can sprout into diseased seedlings or not sprout at all.

In the control of Cassava Mosaic Disease, ensure you select cassava varieties that produce branches as sources of planting material. Most of the stem cuttings from these branches will sprout without the disease. On the other hand, most of the stem cuttings from the main stem will sprout when already infected.

If planting cassava varieties that do not branch, avoid the stem cuttings, especially sections near the base of the stem as planting material for similar reasons as explained above.

Planting

When cutting up cassava stems into stem cuttings for planting, you should select the middle brown-skinned portions of cassava stems. These parts sprout and ensure more vigorous plants than the top green stem portions. The top green stems dry out quickly and are easily damaged by disease. It is advisable to plant cassava early, at the beginning of the rains. Early planting allows the crop to grow more vigorously and better withstand disease damage later in the dry season than late planting.

Managing the crop

After planting, closely observe the stem cuttings as they sprout. Normally, stem cuttings sprout 3–4 weeks after planting. Label all the plants, which sprout without the disease. At harvest time select these as your planting material to control Cassava Mosaic Disease. Even if the plants sprouting without Cassava Mosaic Disease are attacked by the disease later on, they will grow into healthier plants than those that grow from stem cuttings sprouting with the disease.

IPM practices after planting

Good farm sanitation helps to reduce the sources of the pathogens that cause cassava diseases in farms. For example, after root harvest you should destroy cassava stems with shoot tip dieback, cankers, fungus patches, streaks or any other disease symptom.

Crop debris of storage roots, leaves, and stems with these symptoms harbour the pathogens and should be destroyed to reduce the sources of disease spread. Farm tools should be cleaned before and after planting to reduce the spread of root rot fungi through tools contaminated with the pathogen. If only a few stem cuttings sprout with disease, it is advisable to remove and replace them.

Important disease control measures in cassava

  • Identify the common cassava diseases, their 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 symptoms of disease.
  • In the control of Cassava Mosaic Disease, select planting material mainly from stem branches; avoid the base of the stem and main stem portions as sources of stem cuttings.
  • Plant cassava mainly at the beginning of the wet season; try and avoid late planting.
  • Go round the cassava shamba and remove all plants with signs of disease. This is called rouging. Rouging of cassava plants is best done at 3–4 weeks after planting.

>> Share your experiences with TOF and fellow farmers. Send email to [email protected],  leave a comment below this article or SMS to 0715 916 136.

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