Rice Cultivation in Sri Lanka

 

RICE CULTIVATION IN SRI LANKA

MAJOR INSECT PESTS AND MITE PESTS OF RICE 

On the basis of the extent and severity of the damage, the following insects are considered as major pests of rice in Sri Lanka.

A pest of young rice seedlings. Adult and nymphs suck the cell sap from the leaf tissues. Damaged leaves roll inwards along the margins, feeding cause 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:

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

Brown Plant Hopper

Heavy infestations produce symptoms of hopper burn. Leaves dry and turn brown after insect feeding, and patches of burned plants are often lodged. It is a vector of grassy stunt and ragged stunt virus diseases. The rice plant is most sensitive to attack at late vegetative and reproductive stages.

The economic threshold for BPH at booting stage is 2 per hill and at heading 5 per hill. Since spiders are considered major predator of BPH, the economic threshold levels are adjusted according to the number of spiders present. Number of effective predators and parasites are known. 

Ptb 33, a variety with a high level of resistance to BPH, is extensively used in the breeding program. A number of varieties with moderate level of resistance to BPH have been developed: Bg 379-2, Bg 300, Bg 403, Bg 304, Bg 357, Bg 358, Bg 360. 

Effective control methods available:

Cultivate resistant varieties.

Draining the paddy field to reduce moisture help prevent BPH multiplication.

Indiscriminate use of insecticides during vegetative stage known to cause BPH outbreaks. Use insecticides only when and where needed during vegetative stage especially for the control of leaf eating caterpillars.

Monitor crop regularly for signs of early BPH infestations.

Select a safer insecticide if required.

Safer and effective insecticides are available for use during epidemics

Yellow Stem Borer (YSB): Scirpophaga incertulas (Lepidoptera: Pyralidae) 

The caterpillars bore into the rice stem and hollow out the stem completely. Attacked young plant shows dead heart and older plants show white heads. Often plants break where the stem is hollowed out causing lodging. 

Serious out breaks of YSB are very rare. Resistant varieties are not available. Effective insecticides are available for YSB control.

Rice Leaffolders (RLF): Cnaphalocrocis medinalis; Marasmia spp. (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

Rice Gall Midge (RGM) Orseolia oryzae (Diptera: Cecidomyiidae) 

coleoptern predatory beetle have been identified.

Severity of damage is related to the crop growth stage of attack. The larvae move 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 cause formation of a gall called a "Silver" or "Onion" shoot. Galls terminate the tiller development and hence affect rice yield. 

Gall midge damage is high in wet humid weather. As such gall midge infestation is high in dry and intermediate zones in maha and in the wet zone during yala. 

Resistance available in varieties like Ptb 18/ Ptb 21 and Eswarakora has been used to develop a number of improved varieties with resistance to gall midge. Since biotype development on resistant varieties is common breeding for resistance is difficult. The gall midge biotype detected after 1986 is termed as biotype II. Varieties resistant to biotype II are: Bg 304, Bg 357, Bg 359, Bg 360. 

Control methods:

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.

Cultivation of resistant varieties in endemic areas is the most economical method.

Paddy bug (PB) Leptocorisa oratorius (Hemiptera: Alydidae) 

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. 

Paddy bug can feed and reproduce only on rice. Adults and mature nymphs can feed and survive on alternate weed hosts. 

A number of predators and egg parasitoids have been identified. Gryon nixoni is the most common egg parasitoid found in Sri Lanka.

Rice sheath mite(Panicle rice mite): Steneotarsonemus spinki smiley (Acari : Tarsonemidae)

Sheath mite can be considered as a serious pest in rice crop causing 5% - 90% yield losses.It is microscopic in size.Sheath mites live in the space between leaf sheaths and feed on the adaxial surface of leaf sheath and developing kernels.High infestation at booting stage of the crop resulted erected by the presence of chocolate brown colour lesions on leaf sheaths.Sheath mite damage the crop indirectly by rectoring pathogenic fungi such as sheath rot causing sarocladium oryzae.

Effective control methods available

Destroy infected stubbles by plugging just after harvesting or by burning.

Sun drying of seed paddy before soaking.

Weed management

Monitor the crop from early booting stage for chocolate color lesions on leaf sheaths.

Single application of recommended insecticides if the signs have been observed.

Crop rotation with leguminous crops such a meeng

Follow the fied for 2-3 seasons if the problem was not controlled with the above measures.

Insecticide recommendations for rice pest control

Pests of Stored Paddy and Rice

Four important species of pests of stored paddy and rice are found in Sri Lanka.

Grain Moth- Sitotroge cerealella 

Infestation of grain moth starts in the field and may reach serious levels in the store. The damage is done by larvae which are elongated, dirty white about 8 mm long. The pupa is dark brown. The adult is a small, straw colored moth about 7 mm long; the wings are 15 mm across when open. Infestation of grain moth could be minimized by sun drying of seeds to minimize moisture content down to 8.0% and pack in polythene or paper bags. 

Grain weevil- Sitophilus granarius 

Two species of stored product pests belongs to genus Sitophilus are found in rice in Sri Lanka. They are Sitophilus granerius and S. oryzae. Infestation of these two species starts in the field. Eggs laid on rice seeds, hatch into tiny grubs which feed the grain. Mature larvae are legless and dirty white about 4 mm long. Pupation takes place in the grain. Adult beetles are small brown weevils. They are about 3.5-4.0 mm long with rostrum. This pest could be controlled by spraying the store with pirimiphos-methyl at the rate of 27 ml per 9 liters of water. Spray gunny bags with the same insecticide and sundry them before use. 

Red flour beetle: Tribolium cestaneum

Red flour beetle is a secondary pest and their damage is extensive in previously holed or broken grains. Both larvae and adults damage the seeds. 

The larvae are yellowish white. The head is pale brown. They are about 6 mm long when fully grown. Pupae are yellowish white at the early stages and become brown in colour later. The adult is flat and reddish brown in colour. This pest could be controlled by following sanitary measures and spraying pririmiphos methyl to the stores and gunny bag before use.