Rice Diseases

Symptoms of affected plants hold the key to an accurate diagnosis of the field problem in question. Symptoms and signs of already recorded rice diseases have been very well described and recorded, and therefore one should use such available literature in relation to present field problem in question. Careful examination should include looking for discoloration, abnormal growth, or wilting of the leaves, storm and insect injuries, lesions, galls or any abnormality on the stem that may result in a disruption in the flow of water or nutrients. Leaf symptoms are often a reflection of root abnormalities; therefore, plants should be carefully dug up and the soil removed from the roots.

Indigenous Rice Farming in Sri Lanka

Seeds and chemical use farming has been course for many problems in Sri Lanka.



Impressions of Sri Lanka by Sooriya



SUSTAINABLE RICE FARMING

Rice Soils of Sri Lanka and their Productivitity

AGRO ECOLOGICAL ZONES SRI LANKA

In Sri Lanka, rice is grown in diverse environmental and soil conditions. from drought prone areas in the Dry Zone to water logged areas in the Wet Zone , elevation from sea level to mountains of about 3800 m above Mean Sea Level (MSL), temperature ranging from about 170 C in upcountry to about 400C in the semi arid DZ and rainfed to irrigated conditions.
Also, rice growing soils are varying from properties such as texture, drainage, nutritional status and edaphic problems. These soils are in various topographical, pedological and hydrological conditions in various land- forms. Because of this diversity, the average rice yields in these lands are ranging from about 2-8 t/ha.

Agro Ecological Zones in Sri Lanka
Sri Lanka experiences in diverse agro ecological conditions. Based on the amount of rainfall received, the country is divided into 3 major zones:
Dry Zone (DZ) Rainfall <> 2500 mm
Also, the country is further divided into three major elevation zones;
Low Country (LC) 0 - 300 MSL
Mid Country (MC) 300 - 1000 MSL
Up Country (UC) 1000 m and above MSL

Taking into consideration of these two parameters (rainfall and the elevation), seven major Agro Ecological Zones have been identified (LCDZ, LCIZ, LCWZ, MCIZ, MCWZ, UCIZ and UCWZ) in Sri Lanka. These agro ecological zones are further subdivided into 24 Agro Ecological Regions, considering the temperature, amount of rainfall receives and its distribution pattern, soil types and the land form pattern. Of these 24 Agro Ecological Regions, rice is grown in all the Agro Ecological Regions except in WU1, WU2, WU3, IU1 and IU2. There are diverse differences in environmental conditions and inherent problems associated with rice growing fields in each of these agro ecological regions.

More info: www.agridept.gov.lk

www.goviya.com

Rice Blast

Found in both upland and lowland environments blast occurs most often in upland environments in Sri Lanka. Water deficiency predisposes the crop to severe infection in all environments. Magnaporthe grisia is the organisum that cause "Rice Blast".

How to manage Rice Blast.

Use of resistant varieties is the first important step in successful disease management program. Application of high amount of nitrogenous fertilizers induces a heavy incidence of blast in disease susceptible varieties irrespective of the supply of phosphorus or potassium.

How to Diagnose rice diseases accurately in the field

What is a plant disease?

An impairment of the normal physiological functioning of a plant or plant part caused by disease causing agents such as fungi, bacteria, viruses or nematodes. Plant diseases can be spread from an infected plant into a healthy plant.

Numerous disease of rice, caused by fungi, bacteria, viruses and nematode have been recorded in literature. Some diseases occur where ever rice in grown. Some are of both regional and international important, others occur in local areas. Some diseases reach epidemic proportion and causes serious crop losses which others causes only negligible crop losses.

Disease Causal organism

Rice blast - Magnaporthe grisea
Rice sheath blight - Rhizoctonia solani
Brown spot - Cochiobolus miyabeanus
False smut - Ustilaginoidia virens
Grain spotting and pecky rice - many fungal species and bacteria
Leaf scald - Gerlachia oryzae
Narrow Brown Leaf spot - Cercospora janseana
Sheath rot - Sarocladium orysae
Root knot - Meloidagane spp.
Bacterial blight - Xanthomonan campestris pv. oryzae
Bacterial leaf streak - Xanthominan campestris PV oryzicola

During the last 30 years major changes have occurred in the varietal composition of and cultural practices for rice in Sri Lanka. Each season the rice crops in farmers fields are affected by many plant disease problems. Effects of plant diseases on rice crop productivity often varies depending on inherent capacity of the variety to withstand the disease condition in question, environmental factors, stage of crop growth, level of soil fertility management and indirect and harmful effects of agrochemicals such as herbicides and other pesticides.

Paddy Bug Damage reduce 3 to 5% of rice yield in the country.

Sucks the developing grains causing empty or partially filled grains. Both nymphs and adults damage the grains. Damage estimated to reduce 3-5% rice yield in the country.

How to control Rice Gall Midge

Rice Gall Midge / Orselia oryzae

Diptera: Cecidomyiidae

coleoptern predatory beetle have been identified,
Severity of damage is related to the crop growth stage of attack. The larvae more down between the leaf sheaths until they reach the apical bud or one of the lateral buds. They lacerate the tissues of the bud and feed until pupation. The feeding causes formation of a gall called a "Silver" or "Onion" shoot.Galls terminate the tiller development and hence affect rice yield.

There are two main Control methods,

1. Granular insecticides are recommended for gall midge control. Since farmers use granules after observing damage symptoms it is difficult to obtain a good control with granules.
2. Cultivation of resistant varieties in endemic areas is the most economical method.

Cnaphalocrocis medinalis

Rice Leaffolders

Lepidoptera: Pyralidae

The caterpillars infest the leaves and feed on the mesophyll. They fasten the edges of a leaf together and live inside the rolled leaf. Feeding reduces productive leaf area that affects plant growth. Cloudy and humid weather, shady locations and high N-fertilizer favor pest build up.

Control measures available

Establish crop at recommended plant spacing
Use recommended dose of N-fertilizer
Monitor crop regularly. ELT
ETL 25% of leaves showing > 50% damage
Use safer IGR for control.

Stenchaetothrips biformis

Rice Thrips

Thysanoptera: Thripidae

A pest of young rice seedlings. Adult and larvae suck the cell sap from the leaf tissues. Damaged leaves roll inwards along the margins, feeding causes leaf drying resulting poor crop growth. The damage is severe under water stress conditions. Late planted crops are more prone for damage. Short duration traditional rice varieties like Dahanala, Kaluheenati, Kalubalawee are resistant to thrips. Higher trichome density on leaf surface found to be responsible for thrips resistance in rice. Effective control methods available.

Control methods

Submerge infested crops intermittently for 1-2 days.
Drag a wet cloth on the seedlings.
Apply recommended insecticides if difficult to control.
For endemic areas use a recommended seed-dressing formulation.