Saturday, October 5, 2013

Insect Pest Of Rice: Rice Leaf Folder Or Rice Leaf Roller

1. larva in action   2. adult rice leaf roller moth
a leaf roll
Rice leaf folder or roller  is considered one of the major harmful insect pest of rice. It is common in maximum rice growing are. It’s scientific name is Cnaphalocrosis medinalis and this insect belongs to the family Pyralidae of Lepidoptera order. These insects do harm when they are at larvae stage. They do harm by rolling leaf and reducing photosynthesis area.

Nature of Damage:
The destructive stage of this insect is the larval stage. At this stage they fold the leaves longitudinally before feeding. They tie the leaf margins with the threadlike silk. They feed the green mesophyll of leaf inside the folded leaf. They feed by scraping. At first and second instar larvae feed within the slightly folded areas of leaf. At late second instar feed and roll up the maximum area of a leaf . There is one larva in one leaf. After feeding one leaf, larva moves to another leaf. In this way one larva can damage a number of leaves. Feeding reduce the photosynthesis area of leaves. So vegetative growth and finally yield is hampered. Yield loss is maximum when flag leaf is damaged.

Control Measure:
1. Though cultural control or method is a effective method, it reduces the population of rice leaf folder or roller but not eliminate the insect totally.
a. Rice leaf roller in takes shelter at grasses and weeds during off season and continue  their life cycle. So we must clean the surroundings of rice field area or we can manage weeds or grasses.
b. Slit and judicious use of N fertilizer is needed.
c. Hand picking of the larvae should be done.
d. Ratooning of rice crop should be avoided. Because these insects will increase their population in ratoon crops of rice.
e. Stubble of rice crops should be avoided.
2. Mechanical control is an effective method to control the rice leaf roller moths. It is suggested by the agriculturist because this method does not pollute the environment as the chemical method does.
We can capture adult moths by light trapping to reduce the population of this harmful insect in our rice fields.
3. Resistant variety cultivation also appreciated.
4. Biological control is best to control rice leaf roller insects. Biological control is the method of controlling an insect population by it’s natural enemy or predator or parasites.
a. Eggs of the rice leaf roller is parasitized by Trichogramma sp. So we may introduce Trichogramma sp. In our rice field to control rice leaf roller when they lay eggs.
b. Larvae of the rice leaf roller is parasitized by Xanthopimla emaculata. So we may introduce Xanthopimla emaculata in our rice field to control rice leaf roller when they are in larval stage.
3. Pheidole sp. ( a sp.of ant ) is a predator of the caterpillars of rice leaf roller moths.
5. Chemical control is not appreciated by scientists and agriculturists. Because chemicals used in crop fields pollute our environment in many ways, do harm to our health and wild lives. This control method is our last step to control the insects when there is a possibility of reducing the yield in huge amount.
Spraying of any following insecticides at economic threshold level of 10% damage leaves:
Fenitrothion at the dose of 454 ml per acre area, Malathion at the rate of 404 ml per acre area, Carbaryl at the rate of 688 g per acre area, Cypermethrin at the rate of 202 ml per acre area.

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