|
Pest control technology for Rice in Goa |
|
Rice forms the staple food in Goa. One of the constraints in rice production is the attack by insect pests. Even though more than 100 species of insect pests are known to attack rice crop at one or more stages of its growth, only about 15 species of insects can be considered of economic significance in this territory.
Important major rice pests
Rice gall midge ( Orseolia oryzae )
The maggot burrows into the growing points of the tillers and transforms them into onion leaf like tabular structures which dry off. The tubular structures are called ‘silver shoot’. Earhead is not formed in plants showing silver shoot.
The adult fly becomes active at the onset of the monsoon and develops 1-2 generation on rice ratoons and grasses and then migrate to newly planted rice. The continuous heavy rainfall during the months of June and July is quite congenial for outbreak of pests especially in susceptible varieties when transplanted late (between the end of July and August).
Early sowing (in second fortnight of May) and early transplanting (in June) of various susceptible varieties Jaya, IR8,IET 2222, Annapurna will help in escaping from this pest.
In gall midge endemic or low lying areas and in areas where delayed planting is practised, it is recommended to grow gall midge resistant varieties like CR 94-721-3 Vikram and IET 7918.
If the susceptible varieties are planted late in July and August, chemical control measures are to be adopted as follows. Apply carbofuran (200 g): or phorate (100) g or guinalphos (200 g) per 100 sq.m nursery on tenth day after sowing and impound the water for three days. Before transplanting the roots of seedlings are to be dipped in chlorpyriphos 0.02%. Repeat the granular application on 15th day to 20th after planting as described above.
Application of granular pesticide is feasible where there is not much water stagnation as well as there is no flow of rain or floodwater.
Procedure for seedling root dip
An area of 3x1 m is marked and bunded strongly on all the sides. A polythene sheet of 3.5 x 1.5 m is stretched on this area and kept in such a way that it forms all shallow flat tub of 3 x l x 0.15m dimensions.
Take 50 litres of water in the tub to which 50 ml of chlorpvriphos 20EC is mixed. Rice seedlings about 250 bundles which are sufficient to transplant 1000 sq.m are kept overnight in the tub with the root portion immersed in chlorpyriphos solution and then transplanted. Alternately, the seedlings can be dipped, in 50 ml chlorpyriphos mixed with 50 litres of 1% Urea solution for 3 hrs and transplanted. A slurry containing 30 kg rock phosphate about 10 litre of clayey suspension, 50;ml of chlorpyriphos and required water can also be used. 'The root portion of the seedlings is coated with thin layer of chlorpyriphos slurry and the treated seedlings are transplanted 5-10 minutes after the treatment. The nitrogen and potassium fertilizers are only to be applied in this case as basal dose in the mainfield. The main field should be well puddled with water standing at 2 cm depth.
Leaf Folder (Cnaphalocrocis Medinalis)
In high yielding varieties, the pest occurs throughout the crop growth. But the incidence is relatively more at boot leaf stage. The larvae fold the leaves and feed on the chlorophyll from inside the folds. The damage appears as white patches in a field. In severe cases the folded leaves present a scorched up appearance. The severity of incidence depends generally upon the rainfall. If the intensity of rainfall is heavy and continuous in June and July, the pest attack will be negligible. On the other hand, if the intensity of rainfall is less or if there is a short break of about a week or more in the monsoon during June July period, the outbreak of this pest can be predicted well. If the damage exceeds more than one leaf per hill, spraying with phosphamidon (50 ml), or carbaryl ( lOOgm ) or fenthion ( 60 ml) or endosulfan (140 ml) or monocrotophos (120 ml) in 50 litres of water per 1000 sq. m. area was found to be highly effective against this pest. The granules recommended for the control of gall midge are effective against this pest also
Caseworm and blue beetle ( Nymphula depunctalis and Leptispa pygmaea)
Both the pests appear in low-lying areas whenever heavy rainfall occurs during July-August. The case-worm larvae cut the leaf blades into short lengths, construct tubular cases, remain inside these small rolls and feed on the foliage. It is semi aquatic in habits and is able to breathe under water. In a badly infested field, number of these leaf cases, white in colour could be seen attached to the plants. The case worm also appears in Rabi season and causes severe damage. The blue beetle is a small-elongated smooth bluish beetle. Both adults and gubs in large number remove strips of leaf surface causing scorched appearance to the affected leaves. If the extent of damage is more than one damage leaf per hill, the affected field is sprayed with the pesticides recommended for leaf folder.
Grass hoppers (Oxya velox and Heiroglyphus spp)
These are found mostly in kharif rice. The female grasshoppers lay eggs in masses from 30 to 40 under the soil especially along the sides of field bunds during October - December months. These egg masses remain under the soil for several months and hatch into young grasshoppers soon after the first rains in May – June Though active, they are wingless and grow by feeding on the grasses etc. on field bunds until the rice comes up. They migrate to the rice field and defoliate rice plants by removing sections near the edges of leaves. They become winged adults. In Severe cases only mid ribs of rice plants will be seen.
Scraping of bunds, and ploughing up the field during earlier summer months will destroy the egg masses. During crop period, if damage is light to moderate, dusting of BHC W/g @ 2.5 kg or spraying of dichlorvos ( 50 ml) or endosulfan ( 140 ml) or monocrotophos ( 120 ml ) in 50 litres of water for 1000 sq. m. area will be quite effective in controlling this pest.
Brown plant hopper (Nilaparavate Lugens)
The outbreak of brown plant hopper is generally noticed in susceptible varieties like Jaya and IR-8 during August-September when high rainfall coupled with cloudy weather prevails.
Both the numphs and adults of plant hopper congregate and suck the sap at the basal portion of the plant causing hopperburn. As a result the plant vigour is reduced and in severe cases the affected plants die off. The infestation spreads as circular patches and finally the whole field is infested resulting in maximum yield loss.
The field should be inspected at least once in a week during August – September in several scattered hills The base of the tillers should be examined for the presence of small brownish insects for an early diagnosis of the pest. If five or more insects per hill are found, immediate action is to be taken to control this pest. The water is drained out from all the fields simultaneously and alleyways made for every 2-3m. This would change the favourable microclimate for pest into an unfavourable one.
Spray any one of the pesticide as suggested for leaf folder in the evening. While spraying, sprayer nozzle should be directed at the basal portion of plant. The application is to be repeated if hopper population persists beyond a week after application.
The caterpillar appears suddenly in kharif rice in swarms of thousands, completely devours the whole field and moves to another, that is why it is called 'army worm'. Army worms feed on many grass species. This also cuts the panicle at the base and cases serious losses to the rice crop.
The mechanical method of sweeping the worms into baskets and killing then is effective if done thoroughly.
Spray thoroughly with dichlorvos (50 ml) or endosulfan (140 ml ) or monocrotophos (120 ml) in 50 litres of water 1000 mt area during afternoon hours. All the infested fields are to be sprayed simultaneously so as to have an effective control of the pest.
Gundhi bug (Leptocorisa Acuta)
The presence of the bugs in the field is indicated by 'Gundhi' small. Both nymphs and adults attack the paddy ear heads and suck the sap from developing grains. As a result the grain fails to develop and shrivels up partially or completely. Yield loss up to 90% has been noticed in severe cases.
Spraying the affected yield with malathion (100 ml) or carbaryl (100 g) or fenthion (60 ml) or monocrotophos (120 ml) in 50 litres of water per 1000 sq. m area during afternoon hours will check the pest.
|