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Insect pests
Introduction
The incidence of insect damage is more severe in hybrid cotton than varieties. Among varieties, the damage by insects varies according to species in following order.
G. barbadense, G. hirsutum, G.arboreum, G. herbaceum
- Only Chemical control of pests is not possible. Cultural methods like appropriate time of sowing, thinning at proper time, proper spacing, deep ploughing, removal of alternate hosts, burning of stubble after harvest, trap cropping or healthy intercropping are useful methods to reduce the insects population/attack.
- Indiscriminate use of insecticides alone can only aggravate the insect damage – leading to discontinuation of cotton cultivation itself.
- Karnataka stands as a live example for negative impact of indiscriminate use of insecticides. In 1977-78, Cotton area in Karnataka was 10.44 lakh ha. It dipped to 9.14 lakh ha. During 1986-87 and later stabilized to 6.50 lakh ha. This was mainly due to absolute discontinuation of cotton cultivation in Raichur and Bellary districts due to unmanageable boll-worm attack – which was the result of indiscriminate use of insecticide
- For successful control of cotton insects – a comprehensive approach involving all possible cultural methods, eco-friendly pesticides as well as selectively use of insecticides (with proper dosage) has to be adopted. Control of an insect has to be based on damage level and economic threshold limits decided for different insects.
Although more than 130 species of insect pests are known to attack Cotton, following insect species are more prevalent in South India.
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Bollworms
American boll worm, Helicoverpa armigera Hubner
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Nature of Damage
- Larval damage to square, flowers and bolls cause their extensive shedding.
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Spotted boll worm, Earias vittella. Fabricus spiny boll worm, E.insulana Boisdual
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Nature of Damage
- Larvae bore into the stem from the terminal bud leading to the death of terminal portion of main shoot.
- Lateral branches grow out and plants have bushy growth.
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- During flowering phase, larvae go into the flower buds and feed on their contents, causing shedding of squares.
- They also damage the young fruits (boll), causing shedding.
Pink boll worm, Pectinophora gossipiella Saunders
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Nature of Damage
- Larvae enter into flowers. Such flowers do not open properly due to internal webbing of petals, causing characteristics rosette formation of flowers.
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- Larvae enter very young fruits, feed on the seeds, destroying their viability in northern zone, they also join two seeds and hibernae as larvae.
Control
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Dosage Rate (GAI/ha) |
Stage of the crop |
Boll worms |
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| Neem products (300 ppm) |
2.5 lit |
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| Endosulphan 35 E.C |
875-1050 |
40-60 days |
| Quinalphos 20 AE |
700-900 |
40-60 days |
Chlorpyriphos 20 E.C. |
500-700 |
During fruiting stages |
| Carbaryl 50 WP |
1000-1250 |
During fruiting stages |
| Profenofos 50 E.C. |
500 |
During fruiting stages |
| Deltamerthrin T, 8 E.C. |
10-12.5 g.a.i/ha |
As ovicide |
| Alphamethrin 10 E.C. |
15-25 g.a.i/ha |
Above 75 days only once or twice in the Cropping period |
| Cypermethrin 10 E.C |
40-60 g.a.i/ha |
Fenvalerate 20 E.C |
75-100 g.a.i/ha |
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Defoliators
Leaf roller : Sylepta derogata (Pyrsultidae : Lepideptera)
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- The Larvae rolled the leaves and feed on the green matter by scraping. only one larvae is seen in each leaf roll.
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Semilooper : Anomis flava (Noctuidae : Lepidoptera)
- Larvae which feeds on the leaves and detoliate the plants.
Grross hopper : Cyrtocanthacris ranacea (Acrididae : Orthoptera)
- Initially the grosshopper feeds on grasses later it occurs on plant and feeds on leaves.
Hairy Caterpillar : Euproctis fraterna
- Initially the larvae scrape the green matter results in Skelitonization, later it moves on other parts of the plant and defoliate.
Control measures for defoliators
- Spraying of contact insecticides like quinalphos 0.05% or chlorpyriphos 0.05%, etc.
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Spodopetra
Spodoptera litura Hubner
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Nature of Damage
- Larvae cause damage by feeding on leaves as also on fruiting bodies.
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Control
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Dosage Rate (GAI/ha) |
Stage of the crop |
| Spodoptera and others |
Chlorpyriphos 20 E.C
Quinalphos 20 AF
Diflubenzuron 50 WF
Poison bait using
Monocrotophos 36 |
500
500
75
250-500 |
For early instars only
Early and grown up larvae |
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Stem feeders
Stem weevil : Pempherulus affinis (Curculionidae : Coleoptera)
- The grub tunnel round the stem feeding on the soft tissue and this results in the formation of gall like swelling at the site of injury. About 20-25 percent of plants die in severe infestation.
Shoot weevil : Alcidodes affabar (Curculionidae : Coleoptera)
- The grubs bore into top shoots and leaf axils results in affect the growth and death of young plants.
Ash weevil : Myllocerus sp. (curculionidae : coleoptera)
- The grubs attack the roots of cotton plants and the adults feed on leaves. As many as ten seedlings are damaged by a grub. The attacked plants wilt and dry up.
Control measures for stem feeders
- Remove the affected branches / plants and destroy.
- Restriction of the period of crop.
- Spraying of quinalphos 0.05% or chlorpyriphes 0.05%, etc.
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Sucking Pests
Leaf hopper : Amrasca biguttula biguttula (Cicadellidae : Hemiptera)
Damage Symptoms
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- Both adults and nymphs sucks the plant sap from lower/under surface of leaves resulting yellowing and curling. In severe cases, it produces "hopper burn".
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Aphid : Aphis gossypii (Aphididae : Hemiptera)
- Aphids present on the tender shoots and the under surface of leaves in very large numbers and sucks the sap. Severe infestation results in curling of leaves, stunted growth and gradual drying and death of young plants. "Black sooty mould" develops on the honey dew of the aphids which falls on leaves.
Whitefly : Bemisia tabaci (Aleyrodidae : Hemiptera)
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- In cotton the nymphs are found in large numbers on the under surface of leaves and suck the sap. In severe cases, infestation results in premature defoliation, development of sooty mould on honey dew excreted, and shedding of buds and bolls and bad boll opening.
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Cotton mite : Tetranychus neocaledonicus (Tetranichidae : Acarina)
- Nymphs and adults suck the sap from the leaves, later produce purplish red patches.
Thrips : Thrips tabaci and Scirtothrips dorsalis (Thripidae : Thysanoptera)
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- The first species infests flowers and the second infests the leaves. Nymphs and adults lacerate the tissue and suck the sap. In severe attack the leaves curl up and become crumpled.
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Red cotton bug : Dysdercus cingulatus (Pyrrhocoridae : Hemiptera)
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- Both nymphs and adults suck the sap from tender ripening bolls and cause staining of the lint and make the seeds unfit for sowing. A bacterium Nematospora gossypii enters at the site of injury and stains the cotton fibre.
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Dusky cotton bug : Oxycarenus hyalinipennis (Lygaeidae : Hemiptera)
- Adults and nymphs suck the sap from developing seeds in open bolls and also stain the lint.
Control measures for sucking pests
- Spraying of systemic insecticides like, Metasystox 0.05% or Dimethoate 0.05% or Methyl parathion 0.025% or Monocrotophos 0.05% etc.
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Whitefly
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Nature of damange |
Whitefly, Bemisia tabaci Genius |
Both nymphs and adults feed on cell sap. Chlorotic spots develop on the affected areas on the leaves. Such leaves shed prematurely. |
Recommended pesticides in cotton
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Dosage Rate (GAI/ha) |
Stage of the cropNature of damange |
| Whitefly |
Neem products (300 ppm)
Triazophos 40 E.C.
Acephate 75 SP 290 |
2.5 lit
600-800
600-800 |
As and when ETL is crossed
As and when ETL is crossed |
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IPM for cotton whitefly
ETL
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- 5-10 adult flies /leaf
- Field sanitation
- Remove alternate hosts like Hibiscus sp. Sida sp and Abutilon sp
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- Grow bhendi as a trap crop (1 row of bhendi & 10 rows of cotton)
- Growing of cowpea with cotton to increase the predatory population
- Donot apply excess nitrogenous fertilizers
- Follow recommended spacing and fertilizer application
- Avoid the use of synthetic pyrethroids because they develop pest resurgence against mites and whiteflies and also affects the predators.
- In endemic area, avoid varieties having dense leaf cover and having lot of hairs on the plant because they encourage the multiplication of whiteflies.
- Release Chrysoperla (5000 eggs/acre)
- Application of granular insecticides (corbofuran/phorate) for safer to predators.
- Spray the crop with neem oil (3 ml/lit.)
- Spraying of systemic insecticides like Dimethoate, 0.03%, or Metasystox 0.025 % or monocrotophos 0.05%, etc.
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Integrated Pest Management
A practicable module of integrated pest management has been worked out for Karnataka state in which the IPM components are arranged in a logical manner and is being demonstrated on cultivators fields. The salient features of this module are as under;
- Early sowing of suitable hybrid cotton, with okra as a trap crop.
- Seed treatment and spraying systemic insecticides to control sucking pests on need based system.
- Releasing Trichogramma parasitoids @ 2.5 lakh/Release/ha at 5-7 days interval, 3-4 times between 50-65 days after sowing.
- Establishing pheromone traps at 50 days after sowing to monitoring Heliothis activity @ 5 traps/ha. Change the lures every 20 days.
- Spraying neem based insecticides at 65-70 days after sowing.
- Set up pink bollworm pheromone traps at 70 days after sowing @ 5 traps/ha and change the lures at 20 days interval
- Spray Heliothis NPV at 75-80 days after sowing @ 500 LE/ha.
- Spraying Thiodicarb 75 WP @ 1 g/lit water at 85-90 days after sowing.
- Spray any one of the synthetic pyrethroids (Fenvalerate or cypermethrin or Decamethrin @ ½ ml/lit OR Alphamethrin @ ¼ ml/lit) or Spinosad @ 0.1ml/lit or Indoxocarb @ 0.25 ml/lit at 95-100 days after sowing.
- Hand pick and destroy the grown up Heliothis larvae.
- Spray chlorpyriphos @ 3 ml/lit at 105-110 days after sowing.
- Spray again with a synthetic pyrethroid at 115-120 days after sowing.
- Spray Endosulfan @ 3 ml/lit water at 125-130 days after sowing.
- Spray carbary/4grams, OR Quinalphos 1.5 ml OR phosolone 3 ml per lit water at 135-140 days after sowing.
- Repeat the sprays if bollworms persist.
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