|Package of Practices
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1. Certain weeds in rice environment are infested with insects that alternatively support rice pest parasitoids in off-season. Nanophyes sp. on Ammania baccifera L. a weed in rice fields have been identified as a reservoir host supporting parasitoids like Neanastatus cinctiventris Girault on gall midge, Trichomalopsis sp. on Pelopidas mathias (Fabr.).
2. Besides, predating directly on rice pests, spiders support certain parasitoids that also attack rice pests.
Paraphylax sp. and Trichomalopsis sp. parasitizing eggs of spiders have also been recorded as egg parasitoids of Oxya sp., a grasshopper on rice.
3. Trichomalopsis sp. and Elasmus sp have been recorded on the chysomelid beetle Lema. sp. a leaf feeder on Commelina sp. a common weed in the irrigation channels and rice fields. Midges on the grass host Paspalum sp., Cynodon sp. and Mnesihia sp. have been identified as reservoir hosts of gall midge parasitoids.
4. Presrvation of such reservoir hosts may be encouraged to conserve the parasitoids.
Intercropping of crop plants like mustard and alsi etc. provide nectar to the parasitoids and support their population.
5. Flowers of certain ornamental plant, Lantana sp. are also visited by scelionids and trichogrammatids for nectar. Some times certain varieties support more natural enemies than other varieties.
6. On several occasions parasitoid population reaches its peak only after the pest population has reached its peak indicating delayed density dependence.
7. Early inundative release of the specific parasitoid under such situation proves beneficial. Some of the factors that adversely affect the activities of natural enemies are indiscriminate or prophylactic use of insecticides, cannibalism, hyper parasitism and the fragile rice ecosystem.
8. Insecticides, therefore, should only be used as a last resort. Between spray and granular formulations the latter is found to less toxic to parasitoids.
9. Practice of seedling
1. Cnaphalocrocis medinalis is the most important leaf folder species of rice crop and is attacked by a large number of natural enemies.
2. Diversification of natural enemies and the extent of their activities appear to be more in rainy season crop than in summer, which possibly restrict the activity of the pest in kharif as compared to rabi.
3. Inundative releases of Trichogramma chilonis @ 1 lakh/ha against leaffoder have been recommended with satisfactory results. Certain parasitoids are more active in a specific season or location than in the other when the pest is available in all the seasons.
4. At Cuttack, activity of Macrocentrus sp and Temelucha philioppines (Ash.) is more in dry season and that of Cardiochiles nigricollis Cameron is more in the wet season.
5. Extent of parasitism due to this parasitoid ranged from 28 to 50%.Occurrence of diapause has been observed in this parasitoid for the first time at Cuttack. Besides parasitizing the host larvae sometimes, females of Goniozus sp. an ecto-parasitoid fed on them before oviposition as predators.
1. The egg-larval parasitoid, Platygaster oryzae (Cameron) has been recognized as one of the important parasitoids of GM and parasitism reached up to 93% during October-November.
2. Mummies of P. oryzae were found in the upper portion of the silver shoots in the rainy months and in lower portion in dry months.
3. P. oryzae and Platygaster sp. occur in fairly large number in the field, but parasitism occurs late in the crop season.
1. Egg parasitism is often very high, whereas nymph and adult parasitism are generally low.
2. Egg parasitoids exert considerable control over BPH population. Among three common egg parasitoids, Anagrus optabilis (Perkins), Oligosita naias (Girault) and Tetrastichus sp. recorded 42% cumulative parasitism in Tamil Nadu.
3. Anagrus sp. and Oligosita sp. were also the common species at Cuttack and their peak activity (65.5% parasitism) was reached towards the end of the season during October and November.
4. The nymph and adults are attacked by several species of dryinids, elenchids and strepsiterans. The incidence of parasitism by dryinids and strepsiterans are quite variable and increase in the latter half of the crop.
1. The Egg parasitoids of yellow stem borer are Telenomus dignoides (Nixon), T. rowani Gahan, T. dignus Gahan, Tetrastichus schoenobii (Ferr.) and Trichogramma japonicum (Ashm.) are quite effective in controlling the pest population.
2. T. dignoides is the most frequent, widely distributed and effective parasitoid of all. The extent of cumulative egg mass parasitism due to all the egg parasitoids reported from different parts of India range from 4.0 to 97.2%.
3. Activity of T. schoenobii was observed towards end of the season parasitizing alone or in combination with other parasitoids. Super-parasitism was never observed in T. dignoides but T. japonicum exhibited it on a few occasions.
4. T. japonicum released @ 1 lakh/ha during kharif increased the extent of parasitism by 0.2 to 5.6%. Observations indicated that the three parasitoids have selective oviposition preferences and avoid multiple parasitism in an individual egg.
5. Studies at CRRI, Cuttack indicated that parasitism of egg masses increased when the artificial placement of eggs masses of stem borer continued in the rice field, especially during the scarcity of moth population. Collection of egg masses and putting them in bamboo cages cum perches encouraged the build up of parasitoid population.
6. During wet season egg mass wise parasitism ranged from 84.6 to 100% and egg wise parasitism from 28.0 to 74.7%. During dry season egg mass wise parasitism was up to 100% whereas egg wise parasitism ranged from 26.0 to 56.0%.
7. In general eggs of YSB laid towards late tillering or early reproductive stage of the crop are parasitized to lesser extent as the rice plants are older and borer eggs are laid towards lower part of the leaf or leaf sheath among the dense foliage.
1. A parasite is an organism that lives in or on another larger living organism (host) and requires only one or partial individual to complete its life cycle without killing the host, but usually debilitating it.
2. Parasites are usually host specific and may be host stage specific also. A parasite that eventually kills the host is called a parasitoid. Generally the insect parasite of an insect is called a parasitoid.
3. A primary parasitoid is any species parasitizing a particular host. Parasitoids have their own parasitoids. A parasitoid that attacks another parasitoid is called a hyper parasitoid or secondary parasitoid. It usually affects the efficiency of the parasitoid.
5. If many individuals of the same parasitoid species attack the host, it is called super parasitism whereas when the host is attacked by more than one species of a primary parasitoid it is known as multiple parasitism.
6. A parasitoid developing on external surface of the body of the host is called an ecto-parasitoid and developing within the body is known as an endo-parasitoid. Certain parasitoids like Goniozus sp. also behave like predators by host feeding before oviposition.
7. In order to supplement the natural biological control release of biocontrol agents are made in the field. Release of large numbers of a biological control agent relative to the numbers of a target species is known as inundative release.
8. Release of large numbers of a biological control agent to supplement the small numbers already present is called augmentative release. In this process beneficial insects are introduced at the time when pest populations are about to build up.
9. Importation and release of biological control agents in an area where they are not already present, with an objective to establish a population is called inoculative release.
No single effective control measure is available. Therefore, integrated measures are suggested.
Use of resistant cultivars
Use of resistant cultivars is the most economic and environment safe strategy for the management of bacterial blight disease. Although several BB R genes have been identified and characterized, the effectiveness of these genes varies due to difference in virulence profile of the pathogen in different geographical regions. In India, a large no. of rice varieties has been released showing resistance /tolerance to bacterial blight.
• Several chemicals including antibiotics have been tested and used for control of bacterial blight disease, but none of them has proved highly satisfactory. But the following measures have been tested in many places which have helped to reduce the disease severity.
• 10kg seed to be soaked in 20lit water containing 1.5gm streptocycline + 20gm captan for 8-10 hours. Seeds to be shade dried before sowing. Up to 95% of seed infection can be eradicated by this seed treatment.
Hot water treatment
• Seed soaking for 12 hours and treating in hot water at 530 C for 30 minute will make the seed free from bacterium and primary infection
Seedling root dip
• It should be done in 0.1% plantomycin.
- Lateritic and alluvial soil favour more bacterial blight diseases.
- Water logging condition encourages disease development.
- Excessive use of N fertilizers from tillering stage to maximum tillering stage encourages disease development.
- Growing of the crop under shade favours disease development.
- Pruning of leaves at the time of transplanting favours disease development.
The causal organism is the bacterium Xanthomonas oryzae pv. oryzae (Ishiyama) Swings et al. According to the new classification system, it has been placed in:
Phylum : Proteobacteria
Class : Gyammaproteobacteria
Order : Xanthomonadales
Family : Xanthomonadaceae
• Water soaked lesions move from tip downwards on the edges of leaves.
• Gradually symptoms turn into yellow and straw coloured stripes with wavy margins.
• In early morning in humid areas yellowish, opaque, turbid drops of bacterial ooze may be seen.
• In Kresek (wilt) phase, leaves roll completely, droop and plants die completely.