Insect Pest Management
Brown Plant Hopper (BPH): Nilapavata lugens (Stal) (Homoptera: Delphacidae)
Heavy infestations produce symptoms of hopper burn. Leaves dry and turn brown after insect feeding, and patches of burned plants are often lodged. 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:.
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
Rice Gall Midge (RGM) 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.
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.
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 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 commonest egg parasitoid found in Sri Lanka.
Insecticide recommendations for rice pest control
Chemical Groups/ generic name/ formulation and recommended pest
RWM - Rice whorl maggot
MC - Mole cricket
CW - Case warm
RSC - Rice swarming caterpillars
RGM - Rice gall midge
Th - Thrips
RLF - Rice leaffolder
RSB - Rice Stem borer
BPH - Brown planthopper
RB - Rice bug
RFC - Rice field crab
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. Sspray 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.
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