Learn about the pests that damage rice and its control.
1. Brown Planthopper, Nilaparvata lugens (Stal) (Hemiptera: Delphacidae):
The brown planthopper is the most destructive pest of rice in South and Southeast Asia, China, Japan and Korea. In India, it has become very serious on the high- yielding varieties of paddy in many States including Uttar Pradesh, Madhya Pradesh, West Bengal, Andhra Pradesh and Tamil Nadu.
Both adults and nymphs feed on paddy, sugarcane and grasses by sucking the cell sap. The brownish adults with brown eyes are 3.5-4.5 mm in length. Their legs are light brown and the tarsal claws are black. The wings are hyaline with brown markings and dark veins. The nymphs are brownish-black in colour and have greyish- blue eyes.
Life-Cycle:
In tropical areas, this pest breeds on paddy crop throughout the year and its population may reach the maximum any time between October and February, depending upon the climatic conditions. In North India, however, the population of this planthopper becomes high in September-October.
The adults remain most active from 10 to 32°C. The females start laying eggs within 3-10 days of their emergence and they deposit eggs in masses, by lacerating the parenchymal tissue. The number of eggs per mass varies from 2 to 11 and a female lays, on an average, 124 egg-masses.
The eggs are somewhat dark and cylindrical, having two distinct spots. The incubation period ranges between 4 to 8 days. The nymphs, on emergence, start feeding on young leaves and after moulting 5 times, they become adults in 2-3 weeks. In South India, the life-cycle is completed in 18-24 days during June-October, 38-44 days during November-January and 18-35 days during February-April.
The coccinellid beetles, spiders, mirid bugs, black ants (Camponotus sp.) and red ants feed on the nymphs of this pest and exercise a limited natural control. Among the predators, mirid bug, Cyrtorhinus lividipennis Reuter (Miridae) and spider, Lycosa pseudoannulata (Bosenberg & Strand) (Lycosidae: Araneae) are quite important. Releases of mirid bug @ 100 bugs or 50-75 eggs/m2 at 10-day intervals have been found effective for the control of brown planthopper.
The presence of 3 predatory spiders / hill has been found to check the population of brown planthopper. A number of egg parasitoids namely, Anagrus optabilis perk. (Mymaridae), Oligaosita sp. (Trichogrammatidae), Tetrastichus sp. (Eulophidae) and Haplogonatopus sp. (Dryinidae) have also been recorded. Haplogonatopus sp. parasitizes both the nymphs and the adults. The white muscardine fungus, Beauveria bassiana (Balsamo) Vuillemin, is pathogenic on N.lugens.
Damage:
Both the nymphs and adults cause damage by sucking cell sap from the leaves which turn yellow. If the insect attacks during the early stages of growth, the entire plant may dry up. It has been noticed that even when the infestation is rather low, the tillering is adversely affected and there is diminished vigour and a decrease in plant height.
Under the favourable conditions of high humidity, optimum temperature, high nitrogen application and no wind, the population increases very rapidly and the hopper-burn is observed in various localities, giving a brownish hue to the entire countryside. The loss in yield may range from 10 to 70 per cent. This insect is known to transmit the grassy stunt virus disease of rice.
Control:
(i) Closer spacing of 15 × 10 cm creates favourable microclimate in field for rapid development of hopper population. Hence, a spacing of 20 × 15 cm should be followed.
(ii) Alternate drying and wetting the field during peak infestation and draining out the standing water from- the field 2-3 times checks the population of the hopper to a large extent.
(iii) Alleys 30 cm wide after every 3 metres of rice planting provide proper aeration to the crop which ultimately restricts the multiplication of the pest. Making of alleys also helps in insecticidal spraying as applicator can move freely in the field.
(iv) Grow resistant varieties.
(v) Spray at economic threshold level of 5 insects per hill, 100 ml of imidachloprid 17.8SL or 625 g of carbaryl 50WP or 2.0 litres of quinalphos 25EC or 2.5 litres of chlorpyriphos 20EC or monocrotophos 36SL in 250 litres of water per ha. Repeat application if hopper population persists beyond a week after application. While spraying nozzle should be directed at the basal portion of the plants. If the damage is noticed at hopper burn stage, treat the affected spots along with their 3-4 metre periphery immediately as these spots harbour high population of the insect.
2. Rice Leaf Folder, Cnaphalocrocis Medinalis (Guenee) (Lepidoptera: Pyralidae):
The rice leaf folder is a sporadic pest. Its greenish caterpillars are very agile and they feed inside the fold made by fastening together the edges of a leaf. The moths are golden or yellowish brown and measure 8-10 mm in length and 16-20 mm in wing expanse. The wings have 2-3 wavy lines characterized by dark bands. In case of heavy infestation, the plants appear whitish and scorched. The pest is distributed in Indonesia, Korea, Malaysia, the Philippines, Pakistan and India.
Life-Cycle:
The moths which are nocturnal rest on the undersurface of the leaves during the day. They lay oval, creamy white eggs singly or in pairs on the leaves and leafsheaths. The eggs hatch in 3-4 days. A newly emerged larva is dull white or light yellow with a brown head. Soon it starts feeding and turns green.
The full-grown larva is slender and measures 20-25 mm in length. It is very active and moves quickly in the leaf fold, when disturbed. The larval stage is completed in 15-25 days. Pupation takes place in loose silken webs in between the leaves or in the leafsheaths. The pupal stage lasts 6-8 days during the active season. The life-cycle is completed in 25-35 days.
Damage:
The young larvae feed on tender leaves without folding them. The older larvae fasten the longitudinal margins of leaf together with a sticky substance and feed inside the fold by scraping the green matter. The scraped leaves become membranous, turn white and finally wither. The heavily infested crop has streaks on the leaves and appears whitish from a distance.
A single larva may damage a number of leaves as it migrates from one leaf to another. As a result of the attack, photosynthetic activity of the leaves is interfered with and the plants are predisposed to fungal and bacterial infections. In northern India, the pest is active form July to October and is at its peak during September-October.
Trichogramma japonicum Ashmead is an effective egg parasite of rice leaf-folder, causing a reduction of 12-60 per cent of its incidence.
Prevention and Control:
(i) Remove grass weeds from bunds around paddy fields.
(ii) Light-trapping of adults helps to reduce the pest population.
(iii) Spray any of the following insecticides at economic threshold level of 10 per- cent damaged leaves- 425 g of cartap hydrochloride 75SG, 875 ml of triazophos 40EC, 2.5 litres of chlorpyriphos 20EC, 1.4 litres of monocrotophos 36SL in 250 litres of water per ha.
3. Rice Earcutting Caterpillar, Mythimna Separata (Walker) (Lepidoptera: Noctuidae):
This insect occurs in Andhra Pradesh, Assam, Orissa, Punjab, West Bengal and peninsular India. The adult is a pale-brown moth measuring 35-40 mm across stretched wings. The full-grown caterpillar is about 39 mm long. The larvae are gregarious in habit and are commonly known as ‘armyworm’.
Life-Cycle:
The eggs are laid in overlapping rows. In Uttar Pradesh, egg, larval and pupal periods have average durations of 2.4, 21.4 and 9.8 days, respectively under field conditions during July-December when the pest is present in the fields. The full-grown larva pupates in clumps of paddy, in cracks and crevices in ground or in loose soil. The total life-cycle is completed in 48.2 days by female and 45.4 days by male. The longevity of the moth is 12.6 and 9.8 days for female and male, respectively. The insect completes two generations during July to December.
Damage:
The damage to the paddy leaves and ears is caused by the caterpillars. The newly hatched larvae feed on the epidermis of the tender leaves. The second and third instar larvae feed by cutting the leaf from the edge towards mid-rib. The fourth, fifth and sixth instar larvae besides damaging leaves also cut off the panicles mostly at the base and hence the name ‘rice ear-cutting caterpillar’. This stage (4th-6th instar) of the insect causes serious loss to the paddy crop. The larvae are shy of sunlight, hide in the ground during day-time and generally feed at night. The damage to paddy crop is caused mostly during September to November.
Prevention and Control:
Spray the crop with 1.0 litre of quinalphos 25EC or 1.4 litres of monocrotophos 36SL in 250 litres of water/ha. As the pest is noctural in behaviour, the spray should be done in the evening hours for getting better results.
4. Rice Caseworm, Nymphula Depunctalis Guenee (Lepidoptera: Pyralidae):
The insect is present in all the rice- growing tracts and may assume serious proportions in certain seasons in fields under swampy conditions. The adult is a small white moth with a wing expanse of 16 mm with pale brown wavy markings. The larva is light green with a light brownish-orange head.
Life-Cycle:
The female lays about 50 eggs singly or in clusters of 4 on the undersurface of the leaves or grasses. The eggs hatch in 4-6 days. The young larvae feed by scraping the leaf surface. The larva makes a cylindrical tubular case out of a portion of the leaf cut out from it and remains inside it, moving with the case on the leaves. It feeds on the leaves and becomes full-grown in 18-22 days. It pupates inside the case which is attached to the base of the tiller and -the adult moth emerges in 5-6 days. The life-cycle is completed in about 5 weeks.
Damage:
The caterpillars cause the damage by feeding upon the leaves. They lead a semi- aquatic life floating in their tubular cases on the surface of water or attached to the stems at or above the water level. The early stages of the crop are damaged by the pest. The leaf blades are eaten away completely leaving only the midribs. In case of severe attack, the tillers become stunted and loose their vigour and often the plants are killed.
Prevention and Control:
(i) Drain-off the water from the field to kill the floating larvae.
(ii) Put some kerosene in the field water and dislodge the leaf-cases by shaking the plants by passing rope or by branches of thorny plant.
(iii) Chemical control measures are same as in case of rice ear-cutting caterpillar.
5. Rice Gall Midge, Orseolia Oryzae (Wood- Mason) (Diptera: Cecidomyiidae):
The rice gall midge or gall midge is found in most of the paddy growing areas in the southern and eastern parts of India. The pest is also present in Pakistan, South-east Asia and Africa. It is, however, extending the area of its distribution and it appeared in Uttar Pradesh for the first time during 1971. The maggots of this fly, as a result of their feeding, produce galls and kill the growing shoots.
Life-Cycle:
The insect breeds on a number of wild grasses and migrates to the paddy crop when it is in the tillering stage. It attacks the crop from May to September in Bihar and from mid-August to October in West Bengal. In the southern States, its maximum attack is between the third week of August and mid-September.
The tiny pink fly lays reddish elongated eggs about 0.5 mm in length, singly or in clusters, on the leaves or on stems. During August to November, they hatch in 1-3 days. The tiny maggots crawl down to the base of the shoot and enter a young bud where they feed for 10-13 days and then pupate. The pupa wriggles its way up with the help of abdominal spines and cuts a hole at the tip of the gall from which the fly emerges after 4-7 days.
The life-cycle is completed in 15-23 days and the adults live for 3-4 days and lay up to 250 eggs. There are 3-5 overlapping generations on the same crop and 5-8 in a year. The insect probably over-winters in the larval stage in stubble in the northern and eastern parts of India. The period of its activity varies in different regions depending upon the weather during August-November.
Platygaster oryzae Cameron (Platygasteridae) is the most important parasitoid of gall midge maggots, causing 50-90 per cent parasitization depending upon humidity and rainfall.
Damage:
In India, this pest attacks the paddy crop with varying intensity in most of the paddy regions. The maggot of this fly enters the stem and reaches the apical point of the central shoot or the tiller, where it develops. Owing to its feeding, some physiological changes take place which hamper the normal growth of the plant.
The central leaf of an attacked tiller becomes hollow and deformed, and there is a swelling or gall formation on the basal portion. Its growth is stopped and the central leaf ultimately turns into a hollow outgrowth, giving a shining silvery colour called ‘silver shoot’. The infested tillers do not bear ears.
Infestation in the early growth phase is known to induce subsidiary tillering after the death of primary tillers. These tillers are also infested. In the long- duration varieties, infestation during the late vegetative phase results in branching of the tillers which bear ears and, thus compensate, to some extent, for the loss in yield. In case of severe infestation, losses upto 50 per cent have been reported.
Prevention and Control:
(i) Careful timing of planting can avoid damage; once past the tillering stage, the plant is not suitable as a host.
(ii) Considerable buildup of midge population on grasses near the rice crop can be avoided by removing the grasses.
(iii) For gall midge endemic areas, seedling root dip in 0.02 per cent emulsion of chlorpyriphos for 12 hours before transplanting protects the crop for 25-30 days.
(iv) Apply insecticides at economic threshold level of 1 gall per m6 in endemic areas or 5 per cent affected tillers in non-endemic areas. Spray 20-45 days after transplanting 625 ml of chlorpyriphos 20EC or 500 ml of quinalphos 25EC in 750-1000 litres of water per ha. Alternatively, apply granules as mentioned for the control of yellow stem borer.
6. Rice Hispa, Didadispa Armigera (Olivier) (Coleoptera: Chtysomelidae):
Rice hispa is distributed throughout India from Andhra Pradesh to Kashmir and is a very serious pest of paddy at certain places. In the Punjab and Himachal Pradesh, this species causes damage both as larva and adult in the districts of Kangra, Gurdaspur, Hoshiarpur, Kapurthala, Ludhiana and Shimla.
The adult is a small bluish black beetle, measuring 5 mm in length and is recognized by numerous short spines on the body, which gives it a characteristic appearance. The legless, creamy-white larvae are not easily seen, because they are concealed inside the leaf tissue.
Life-Cycle:
This pest breeds actively from May to October and hibernates during winter probably in the adult stage. In May, the beetles start laying eggs on nursery plants. The eggs are embedded in the leaf tissue towards the tip. On hatching, the young grubs feed as leaf-miners, between the upper and lower epidermis.
The attacked leaves turn membranous, showing characteristic blisters or blotches. Later on, the attacked leaves wither and die. When the larvae are full-grown, they pupate inside and finally emerge as black beetles. In Bihar, the pest is known to complete 6 generations in a year, but in the Punjab it probably completes 2-3 generations during the paddy season.
Damage:
Apart from the damage caused by larvae as leaf-miners, the adults also feed on green matter and produce parallel whitish streaks on the leaves. The damage starts in nurseries and spreads to the rice fields. The infestation varies from 6 to 65 per cent.
Prevention and Control:
(i) The pest is suppressed if the infested leaf tips are clipped off and destroyed, while transplanting,
(ii) If the nursery beds are flooded, the beetles float and can be swept together with brooms and then destroyed,
(iii) Spray at economic threshold level (1 adult or 1-2 damaged leaves per hill) with 300 ml of methyl parathion 50EC or 1,4 litres of monocrotophos 36SL or 2.0 litres of quinalphos 25EC or 2.5 litres of chlorpyriphos 20EC in 250 litres of water per ha. If the attack continues, repeat spray after two weeks.
7. Rice Root Weevil, Echinocnemus Oryzae (Marshall) (Coleoptera: Curculionidae):
The rice root weevil is a serious pest of rice in southern India. It was first recorded in the northern parts in 1953 at Sirsa (Haryana). It has also been observed to cause damage to the rice crop in Patiala District (Punjab). Besides paddy, it feeds on the roots of certain grasses.
Damage is caused by the grubs which feed on rootlets of paddy plants. They are translucent white and measure about 6 mm in length. There are six pairs of prominent tubercles on the dorsal side of the abdomen.
Life-Cycle:
This pest is active only from July to September and passes the rest of the period as pupa in the soil at depths of 8-20 cm. The weevils emerge in July with the first shower of rain and are seen sitting in large numbers on rice plants at this time. The eggs which are laid on the plant hatch in a few days. The grubs lead an aquatic life and feed on the root-hairs.
Tubercles on the abdomen help them in respiration and they obtain oxygen from the air-spaces inside the roots of the host plants. Grubs are full-grown by the middle of September when they bury themselves deep into the soil for pupation. The pupae emerge next year in July and, thus, the pest completes only one generation in a year.
Damage:
The grubs feed on root hairs of the transplanted crop, thereby affecting plant growth. The infested crop remains stunted and a large number of plants are killed. The crop transplanted in July is more heavily attacked than the one transplanted in August.
Prevention and Control:
Apply 7.5 kg of phorate 10G per ha in standing water.
8. Rice Grasshoppers, Hierogiyphus Banian (Fabricius) and H. Nigrorepletus Bolivar (Orthoptera: Acrididae):
Various species of grasshoppers are widely distributed in India. They are polyphagous and feed on leaves of rice, maize, millets, sugarcane, grasses, sunnhemp, arhar, etc. H. banian is sporadic pest of rice and other kharif cereals in the Punjab. Another species, Oxya nitidula Walker, which is smaller, also appears in pest proportions on the paddy crop in certain years. The other important species in northern India are Aeolopus famulus Fabricius and Acrida exaltata Walker.
Damage is caused by both adults and nymphs. H. banian and H.nigrorepletus are somewhat like locusts but are smaller. The adults are 40- 50 mm long and are shining greenish yellow, having three black lines running across the pronotum. Nymphs are yellowish, with many reddish brown spots in the early stages, but become greenish as they grow older.
Life-Cycle:
Hierogiyphus spp. have one generation in a year and pass the winter and dry part of summer in the egg stage. The eggs are found in the soil and they hatch in June or in early July, a few days after the first shower of the monsoon. On emergence, the nymphs start feeding actively and complete their development in seven stages, within 3 weeks.
The adults are seen feeding voraciously during August and September. When they are two months old, they mate. The female starts laying eggs by inserting her abdomen in the soil. The eggs are laid 5-8 cm deep, in pods, each containing 30-40 eggs. The egg-laying continues from September to November and the adults die soon after, sometime in the winter.
Damage:
The greatest amount of damage is caused during August-September when both adults and nymphs feed on paddy and other crops, causing defoliation. In certain years, they cause extensive damage, moving from field to field over large areas.
Prevention and Control:
Dust carbaryl 5 per cent or malathion 5 per cent @ 25 kg per ha.
9. Rice Bug, Leptocorisa Acuta (Thunberg) (Hemiptera: Coreidae):
The rice bug, commonly known as gundhy bug, is widely distributed in India, the Orient and Australia. It is a serious pest of rice in Uttar Pradesh and some other parts of India. Apart from rice, it also feeds on maize, millets, sugarcane and some grasses. Both the adults and the nymphs cause damage by sucking sap from the leaves and ears of rice.
The adults are slender, about 20 mm long and greenish brown. They have long legs and antennae with four joints. The newly hatched nymph is about 2 mm long and is pale green. However, as it grows, the green colour deepens. The grown up nymphs are very similar to the adults in colour and size, but they are wingless.
Life-Cycle:
The rice bug breeds all the year round on grasses and various other green plants and appears in paddy fields generally in August and is most active from the middle of that month to November. The females lay 24-30 round yellow eggs in rows on the leaves. The eggs hatch in about 6 or 7 days and the nymphs grow to maturity in six stages within 2 or 3 weeks.
The adult bugs live for 33-35 days. Breeding takes place in winter also, but at a slower rate. The pest is essentially diurnal and is most active in the morning and in the evening, seeking shelter during the hotter parts of the day. Many generations are completed in a year.
Damage:
Rice fields severely attacked by this pest emit a repugnant smell which gives to this pest the name ‘gundhy’ bug. The nymphs and the adults suck juice from the developing grains in the milky stage, causing incompletely filled panicles or panicles with empty grains. Black or brown spots appear around the holes made by the bugs on which a sooty mould may develop. This pest attacks the rice crop periodically and the reasons for its abundance in certain years are not known.
Prevention and Control:
The population can be suppressed by killing the bugs by using light traps, collecting the adults with nets and destroying the weeds to remove alternative hosts. Chemical control measures are same as in case of rice grasshoppers.
10. Rice Mealybug, Ripersia Oryzae Green (Hemiptera: Coccidae):
The rice mealy bug occasionally causes heavy damage to the rice crop in many countries including India, Bangladesh and Thailand. In India, the bug is found in Andhra Pradesh, Mysore, Orissa, Madhya Pradesh and West Bengal. Apart from rice, this insect can also survive on various graminaceous weeds growing in standing water or in swampy areas. The nymphs and the adult females, being wingless, look alike. They are plump, oblong, reddish white, soft bodied and have a distinct powdery coating on their body.
Life-Cycle:
In tropical and sub-tropical regions, this insect is found throughout the year in one developmental stage or the other. They reproduce parthenogenetically and the females either lay eggs or simply deposit nymphs in the outer leaf sheath. In India, the females have been reported to lay 126-319 eggs or nymphs, but in Thailand, the number varies from 60 to 280. The mature females have a life span of about 5 days.
The eggs and the young nymphs are whitish in colour and measure 0.3 and 0.4 mm in length, respectively. The duration of the egg stage may range from a few minutes to 24 hours. The nymphs instinctively stay within the egg sac or under the body of the mother for about 2 days. Then, they move away and establish themselves between the leaf sheath and the stem.
There, they feed and complete the nymphal period in 15-34 days. After the last moulting, the female nymphs become sessile and start depositing eggs or nymphs at the same spot. The nymphs which are destined to become males transform into winged adults which fly off without feeding and some also mate with females. Thus, the asexual and sexual cycles are completed side by side.
Damage:
Damage is caused both by the nymphs and adult females by sucking plant sap from the rice stem. This results in stunted plant growth and yellowish curled leaves. When the attack is severe, the ear heads become smothered and are unable to grow out of their sheaths. The damage is particularly intense during drought conditions.
Prevention and Control:
Chemical control measures are same as in case of rice grasshoppers.