Effective disease management in organic rice production

Effective disease management also starts with prevention of attack by ensuring clean planting materials or resistant varieties which should be planted in a clean environment followed by proper field sanitary procedures and good husbandry practises. Normally all cultural practises that enhance plant vigour will enhance its ability to reduce the impact of disease attacks.

Rice can be attacked by different diseases, for example blast, rice yellow mottle virus (RYMV), leaf scald, brown spot, glume discolouration and bacterial leaf blight. Poor variety and seed selection, lack of proper rotation and poor soil fertility management increase the risk of attack to the plant by these diseases. The rice blast and the rice yellow mottle virus are the most important diseases of rice in sub-Saharan Africa, especially under upland conditions. They can affect rice yields and quality, in extreme cases, leading to heavy losses.

a.   Rice Blast (Magnaporthe grisea) is the most damaging fungal disease of rice in Africa, and is transmitted by spores carried by wind or field implements. The fungus attacks all parts of the rice plant above the ground causing elongated spots/lesions, pointed at each end, on leaves, nodes, panicles and grains, characterized by ‘burning’ of leaves, stunted growth, empty heads, and sometimes neck rot. In the upland systems, any traditional upland cultivars and improved varieties like NERICA show stable resistance to this disease. So the risk from blast is only common with other improved varieties of low resistance and some lowland varieties. Prevention can be achieved by avoiding excessive application of nitrogenous fertilisers (manures) and by keeping the field weed free as some weeds are alternate hosts to the fungus. Also, remove and burn all straw infected fields and restrict movement of tools from infested to healthy fields.

b.   Rice Yellow Mottles Virus (RYMV) is transmitted from an infested plant to a healthy plant by insect vectors, mainly beetles, and causes the selective yellowing and mottling of leaves, stunted growth and reduced tillering. Control can be achieved by using resistant varieties and by removing and burning infected rice plants from the field.