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Details: Category: Pests & Diseases | Published: 20 May 2013 | Hits: 1695

RICE DISEASES AND THEIR MANAGEMENT/ Mary Goretti

Introduction

The major rice diseases in Kenya is Rice Blast  and  other important diseases: Bacteria leaf Blight , Brown spot, Alternaria leaf spot , Stem Rot and Yellow mottle virus and some of the symptoms appear below

1. Rice blast

Distribution: all rice growing ecologies in Kenya.

Symptoms   
Lesions appear on leaves; the tips of lesion are typically spindle-shaped wide in the centre and pointed at the ends. Large lesions usually develop a grey centres bordred by brown to dark red margins.

Management strategies:
Use of resistant varieties Use clean seed for planting

Use recommended spacings (20 x 20cm) at planting to enhance aeration and light penetration

Use recommended dozes of nitrogen for the respective area.

Maintain clean fields as sone weeds (wild rice, eleusine spp and other grases) are alternate hosts which can be sources of infection.

Do not work in the field when it is too wet

Burn or bury infected crop debris.

Chemical control

Fungicide application 2 vegetative stage (35DAT) and Booting Stage (70DAT)

2. Bacterial  leaf spot   

Symptoms
Yellow to white water soaked stripes at the margins of infected leaves.

Later the stripes enlarge and coalesce to give the characteristic yellowish lesions mainly in the upper part of the affected leaves. At times the entire leaf may turn whitish to greyish and die. In severe cases the whole field seems to have been burnt

Management strategies

The disease starts from infected seeds. It is spread between plants and fields by wind, rain, irrigation, water floods.

Use resistant varieties

Observe field sanitation - removal of weeds which can be carriers, and previously infected crop residues.

 
3. Brown leaf spot

Symptoms
Disease start as small, circular, dark brown or purplish dots onleaves. Fully developed lesions are brown, with grey or whitish centres. Most spots have a light yellow halo around.

Management strategies

Proper application of fertilizers, good water management and soil amendments can reduce disease severity.

Resistant varieties are available and can be used

4. Rice yellow mottle virus    

Symptoms
Leaves turn yellow, with alternate yellow and green stripes that give its typical mottled appearence to the plant. Other symptoms are stunting, reduced tillering, leaf mottle with yellow stripes, incomplete anicle insertion, badly formed panicle and spikelet sterility.

Management strategies

Use of resistant varieties such as Resistance varieties- Basmati 370 and 217 , ITA 310

Destroy wild rice and grass weeds which are alternate horsts.

Avoid continous rice cropping – Preferably plant other crops during off season to avoid building up of vectors.            

5. Sheath rot

Sheath rot symptom
Infection occurs on the uppermost leaf sheath at late booting stage. Symptoms start as irregular spots with gray centres and brown margins or gray brown throughout.

Severe infection cause panicles to be only particially inserted, rotted and produce poorly filled grains. Powdery fungal growth is seen inside the leaf sheath.

Control strategies

INTEGRATED MANAGEMENT OF RICE DISEASES

Integrated rice disease management (IDM) is the combination of different methods to control diseases in a cost effective way, based on sound environmental management. None of the methods can by itself ensure efficient and sustainable protection.

The methods often combine varietal resistance, crop management techniques and modest use of chemicals.

Integrated disease management strategies

Appropriate sowing or transplanting date to avoid flowering Coinciding with high atmospheric humidity which is favourable to blast infestation.

Syncronized sowing and transplanting to avoid build up of insect pests that can transmit diseases such as RYMV.

Using heathy or treated seed – fungal and bacterial diseases can be transmitted via seed.

Destruction of weeds and crop residues that can act as reservoirs for pathogens and insect vectors.

For more information