Rice blast is a fungal disease caused by a plant pathogenic fungus called Magnaporthe oryzae. Although it may attack other plants belonging to the grass family, Rice blast primarily infects rice, at all stages of growth and development. However, severe damages occur during the seedling stage.
Under favourable environmental conditions, the disease infection can cause total crop failure.
The fungus infects as spores which produce spots or lesions on the leaves, leaf collars, panicles, culms and culm nodes. It penetrates the plant using a structure called appressorium and sporulates from the attacked tissue to be dispersed as conidiospores.
This cycle repeats itself after overwintering and a single cycle can take about a week, under favourable conditions.
The pathogen can reproduce both sexually and asexually.
SIGNS & SYMPTOMS
Infection on the leaf leads to formation of diamond-shaped or spindle-shaped spots which have gray or white centres and brown margins. These spots coalesce and may eventually cover the entire leaf causing its death.
Leaf collars rot causing premature leaf fall.
When infected, the panicle turns white and dies before grain filling. The rachis, rachilla and grains may also be infected. If the basal node of the panicle is attacked, this results into neck rot and white heads in which bluish-grey fungal growth and sporulation occur.
Attacked nodes rot, causing death of the above plant parts.
Intermodal infection of the culm occurs in a banded form.
Symptoms are visible on all above ground parts of the plant.
Spots develop rapidly under moist conditions producing large numbers of spores.
With respect to the losses attached to infections by rice blast disease, it is of importance to find out how best the disease can be prevented and /or controlled.
The use of fungicides is the most preferred because it is more reliable.
Several fungicides are recommended for use against this disease to both prevent as well as cure it. These include;
- CHARIOT 500SC 20ml/20l
- RANSOM 600WP 15g/20l
- DEFACTO 500EC 20ml/20l
- EXEMPO CURVE 250SC 15ml/20l
- GODDARD 350SC 15ml/20l
- JUPITER 125SC 15ml/20l
- MEGAPRODE LOCK 525WP 20g/20l
- SACRIFIDO 125EC 15ml/20l
Planting certified seeds, which are disease free
- Plant resistant or tolerant varieties
- Use disease-free planting materials
- Ensuring proper spacing
- Practising crop rotation with non-host crops
- Splitting the applications of Nitrogenous fertilizers
- Burning of the diseased plants
- Ensuring proper weed control (weeds serve as alternate hosts for the pathogen)
In order to prevent the pathogen from developing resistance or tolerance against any of the fungicides, alternate various fungicides which have different active ingredients.
- Always mix the fungicide with INTEGRA 3ml/20l. This is a spreader, a sticker, wetter and a penetrant, which helps improve the effectiveness of the chemical.
- Timely control of the pathogen is very essential.