Planthopper- the foe of the paddy field-Erakina

INTRODUCTION

Planthoppers, from the family of insects, named  Homoptera: Delphacidae is a great threat to the farmers who cultivate rice crops. They feed on the rice crop and extract the nutrients of the crop by sucking its sheaths. There are two types of planthoppers the Brown planthopper (scientific name: Nilaparvata lugens) and the white planthopper ( scientific name: Sogatella furcifera).

It is normally found in the base of rice plants from May to September. The adult insects appear during the summer season and multiply vigorously and damage the crop resulting in a low yield. Unlike the leafhoppers that have an entire row of spines on their hind legs, they only have a couple of spines on their hind legs. The adults are ¼ inch long and may appear in white, green, bluish, brown or mottled colour.

Their wings appear like the shape of a leaf and have tiny pointed heads. The flat, wide and wingless ones are nymphs. They leap 2 feet once they are disturbed. The young planthoppers grow into adults with short wings and can’t fly. The lifecycle of this insect varies during different periods   18 to 24 days from June to October, 38 to 44 days between November and January and 18 to 35 days between February and April.

A female planthopper can lay more than 700 eggs in its lifetime.

COMMON THREATS TO THE RICE CULTIVATION

Rice is a staple food of more than 3.5 billion people around the world. They are cultivated mainly in China, India, Indonesia and Bangladesh and lesser amounts are grown in Japan, Pakistan and other Southeast Asian countries too. India ranks 2nd in the production of rice with 20.97% of the total contribution in the world.  China contributes 28.06% of rice production and stands first.

Indonesia produces 9.52%, Bangladesh with 7.07% and Vietnam contributes  6.06%.In India rice is grown in almost half of the states. West Bengal is the highest rice producer in India with almost half of the arable land being under rice cultivation and contributing 15% of the total rice production in the country. Rice is grown from June, August to October-December in the states of Andhra Pradesh, Karnataka, Kerala and Tamilnadu.

They are grown primarily in the Delta region, plains of Assam and surrounding hills, foothills and Terai region of the Himalayas. Clay soil is best suited for its cultivation. Rice cultivation requires a warm humid climate with a temperature of 20 degrees and 35 degrees Celsius and a rainfall of 100 cm.Now let us see what are the main reasons that affect rice cultivation all over the world.

Apart from the regular increase in the price of fertilizers, costly agricultural equipment, lack of credit facilities for farmers, and scarcity of water due to failed monsoons, there is another important threat to rice cultivation. It is the increasing growth of planthoppers in the paddy field that if unnoticed leads to 100% crop loss. In 1970 and 1980 the brown planthopper caused a great threat to rice cultivation all over the world.

These insects damage the rice and transmit two viruses named rice ragged stunt and rice grass stunt. The white-backed planthoppers outbreaks were recorded in Pakistan in 1978, Malaysia in 1979 and  India in 1982,1984 and 1985.

The female insects lay eggs in masses in the midrib of the leaf blades. These eggs are slightly curved in the form of a crescent and are 1mm long Sometimes white or brown nymphs are also found. These insects are tiny and most farmers fail to notice unaware of the total damage they could cause to the entire field. The infected sheaths first turn orange-yellow initially and then turn brown and dry up quickly. This condition is called hopper burn which destroys the entire crop.

The excess use of nitrogen in the fertilizer, an early spray of insecticide and dense growth of crops also increases the population of these insects.

WAYS TO ERADICATE PLANTHOPPERS

• First of all, it is always essential to monitor the crops regularly for the existence of these planthoppers. A thorough check of the plant surfaces particularly below the leaves should be done. A close watch for cottony white masses and waxy or sticky honeydew is a must.

• A strong blast of water from the garden hose should be sprayed to wash off the eggs laid.

• In some cases, flooding of the seedbed is done for a day to control these pests.

• A yellow sticky trap should be scattered throughout the cultivated area to find out the intensity of the planthopper in the field. These traps will reduce the population of the insects and they should be replaced every week to control their growth.

• Add 5 tsp of non-decreasing liquid dishwashing soap solution to 2% of insecticidal soap solution to a gallon of warm water and after mixing them evenly pour them into a spray bottle and spray them on the affected plant surface.

• This should be done in the early mornings and after 2 hrs they should be completely washed off using water to avoid any chemical reactions to the crop.

• Keep repeating this method every 4 to 7 days until the insects disappear.

Conclusion

The outbreak of these insects after using the insecticides named Abamectin and cypermethrin was identified by the Thai government and restrictions were imposed. The IRRI( International Rice Research Institute) also approved this and an action plan was done to reduce the increasing number of planthoppers.

Chess, a  popular and effective insecticide is widely used to control these insects providing longer protection and higher yield. Researchers are performing various experiments to find out the ways to control these pests and identify the chemicals that would decrease their existence and improve the growth of the rice crop.

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