The major insect pests of cotton, their nature of damage and appropriate control measures are given below:
1. American Boll Worm (Helicouerpa armigera):
This is a major pest of cotton which is active from July-October and February-April. For 65-100 days old crop, one egg or larvae per plant or 5-10 % infested fruiting bodies is the ETL.
Nature of Damage:
The larvae feed on the leaves initially and then bore in to the square/bolls and seeds with its head thrust into the boll, leaving the rest of the body outside. A single larva can damage 30-40 bolls. The entry holes are large and circular at the base of the boll.
Control Measures:
Deep ploughing and follow clean cultivation to expose the resting pupae, crop rotation and avoidance of ratooning reduces pest population.
Use tolerant varieties. Trap cropping with crops like tomato, and destroying them when the population is high. Use of maize, and cowpea on borders and wild brinjal and setaria as intercrop significantly helps in reducing the pest population. Harvested cotton from damaged boll should not be kept with good quality cotton. Never pick wet cotton. On dew days, pick cotton in late mornings to avoid moisture in cotton.
Release of egg parasitoids like Trichogramma chilonis or T. brasielenis or T. achaea @ 1,50,000 /ha from 45th day onwards at 10-15 days interval (6 releases) and larval parasitoids such as Chilonus blackburni or Bracon breuicornis or Telenomus heliothidae or Carcelia illota or Coteria kazat or Campoletis chloridae @ 2000 adults/ha at 15 days interval. Release pupa parasitoids Brachymeria sp. Release of the predators Chrysoperla carnea or Scymnus sp. or Eulophids would suppress the population of larvae.
Spray HaNPV @ 250 LE/ha from 35 to 60 days of crop stage. Application of fungal pathogens like Beauveria bassiana or Neumorea riley under humid conditions is effective. Use 5% neem seed kernel extract (NSKE). Endosulfan 35 EC 2.5 lit/ha; or quinalphos 25 EC 2.0 lit/ha; or chlorpyriphos 20 EC @ 2 lit/ha; or cypermethrin 10 EC 600-800 ml/ha or trizophos 40 EC @ 1.5 lit/ha insecticides are effective against the pest.
2. Pink Bollworm (Pectinophora gossypiella Saunders):
This is a major pest which is active from October – November.
Nature of Damage:
The damage is caused by the caterpillars by feeding on the flower buds, panicles and boils. The holes of entry close down by excreta of larvae which are feeding inside the seed kernels. They cut window holes in the two adjoining seeds thereby forming “double seeds” and finally damage them. The attacked buds and immature bolls drop off. Lint is destroyed, ginning percentage and oil content are impaired. For 65-100 days crop, 5-10% infested fruiting bodies is the ETL.
Control Measures:
Clean cultivation and destruction of crop residues (fallen leaves, twigs etc.) before the onset of season Plough deeply to expose the hibernating larvae/pupae. Avoid late sowing of the crop. Early sowing helps in early maturity facilitating escape. Use tolerant varieties (Khandwa-2, JKH-1, Abadita, LH 900, Sujay and desi cotton). Withholding irrigation water to avoid prolonged late boll production/formation to reduce the buildup of over-wintering population.
Use pheromone traps baited with insecticides to kill the pest/ monitor pest population. Release of egg parasitoids Trichogramma chilonis or Bracon elechidae or Elasmus johnstoni or pupal parasitoid Microbracon lefroyi would keep in check the population of PBW. Encourage the activities of predators Chrysoperla carnea or Scymnus sp. or Triphles tantilus or Pyremotes ventricosus (mite) or release them in the fields.
Hot water treatment of the seeds up to 60°C kills the hibernating larvae. Treat the seeds with aluminium phosphide. Application of insecticides like chlorpyriphos 20 EC or endosulfan 35 EC or triazophos 40 EC @ 2.5 l/ha spray.
3. Tobacco Caterpillar (Spodoptera litura Fab.):
It is found throughout the year. Set-up pheromone traps to monitor the ETL.
Nature of Damage:
The larvae feed gregariously on the under surface of the leaves and skeletonize them leaving only the mid-rib and veins in severe cases. They also attack flowers, buds and squares causing considerable loss.
Control Measures:
Plough deeply to expose the pupae and hibernating larvae. Mechanical collection when larvae are feeding in groups, i.e., the younger larvae. Collection and destruction of egg masses. Set-up pheromone traps. Release egg parasitoids Trichogramma sp. (1.5 lakh/ha) and larval parasitoids Chelonus blackhurni or Telenomus remus.
Release of predators Chrysoperla carnea @ 50,000/ha. Spray Spodoptera NPV @ 250 LE/ha. Spraying of insecticides endosulfan 35 EC @ 600-750 ml/ ha effectively reduces the population. Spraying synthetic pyrethroids fenvalerate 20 EC @ 400-500 ml/ha or cypermethrin 10 EC or decamethrin 2.8 EC @ 600 – 700 ml/ha is also effective.
4. Spotted Bollworm (Earias insulana Boisd, Earias vitella Fab.):
These are major pests of cotton, E. vitella is abundant in high rainfall areas and E. insulana in areas of scanty rainfall. The pest attacks the crop from 35-110 days of age.
Nature of Damage:
The caterpillars cause damage by boring into the growing shoots, buds, flowers and bolls. The attacked shoots wither, droop and ultimately die, and flowers and buds drop off. Infested bolls do not shed, open prematurely and the quality of the lint is spoiled due to rot setting. Sometimes pupation takes place in the bolls itself impairing the development of bolls.
Control Measures:
Plough deeply to expose resting pupae. Avoid use of nitrogen fertilizers at the reproductive stage. Use resistant varieties. Planting trap crop of bhendi, uprooting and burning it when the larval population reaches its peak reduces infestation.
Don’t extend the crop period. Collection and destruction of plant debris and trash before sowing. Collection and destruction of infested bolls. Set-up pheromone traps @ 10/ha for monitoring the ETL and timing of spray. Set up bird perches.
Release egg parasitoid Trichogramma chilonis, T. brasiliensis, and larval parasitoids Chelonus blackburni or Bracon brevicornis or Apanteles sp. at 35 to 70 days. Conserve and encourage the activity of the spiders Thomisus sp. and Neosiana sp.
Spray insecticides like endosulfan 35 EC or triazophos 40 EC @2.5 l/ha or cypermethrin 10 EC @ 600-800 ml/ha. Avoid use of conventional sprays repeatedly. Use neem based insecticides like 5% neem seed kernel extract (NSKE) and commercial neem based formulations @ 500-600 ml/ha, starting from 45 days age of the crop or when ETL is reached.
5. Jassids (Amrasca biguttula biguttula):
Pest attacks the crop during 1-50 days age and attack is severe during winter.
Nature of Damage:
Both adults and nymphs suck sap from the underside of the leaves and devitalize the plants. Leaves turn pale, red rust, curls downwards and dry up when infestation is severe.
Control Measures:
Sow the crop early. Use resistant varieties such as Khandwa-2 or the varieties having leaves rich in tannin contents. Do not use high doses of “N” fertilizers. Grow cowpea/onion/soybean as an intercrop in cotton to reduce early stage pest. Use okra (bhendi) as trap crop. Adopt proper crop rotation. Summer deep ploughing to expose soil inhabitating insects. Remove and destroy crop residues/alternate host plants. Use yellow sticky traps. Hand picking and destruction of various insect stages. Destruction of affected plant parts.
Installation of bird perches – “T” shape wooden/bamboo sticks @ 50/ha should be erected for encouraging predatory birds like king crow, mynah and blue jay. Release predator Chrysoperla carnea or Coccinella septumpunctata or Syrphus/cymnus sp. Conserve spiders Distina albida and ants like Camponotus sp. Apply chemical pesticides only if pest population crosses the ETL.
Spray methyl demeton 25 EC or dimethoate 30 EC.
6. Cotton Aphid (Aphis gossypii):
Pest is active from June-October and February- April. Cool weather and humid conditions favour the rapid growth, while heavy rains wash away the aphid colonies. For ETL 15-20% affected plants counted randomly or appearance of honey dew on 50% plants.
Nature of Damage:
Both adults and nymphs suck sap from the tender leaves, twigs and buds, and weakens the plants. Leaf crumbling and downwards curling. Each aphid makes several punctures and excretes honeydew which encourages development of sooty mold on twigs and leaves and this leaves a blackened look of the plants. Honeydew attracts ants and sooty mold aids in the development of pathogenic bacteria.
Control Measures:
Avoid late sowing and excessive use of “N” fertilizers. Destroy infested shoots during early stages. Handpicking and destruction of various insect stages and the affected plant parts. Release predator Chrysoperla carnea or Coccinella septumpunctata or Syrphus/Scymnus sp. Conserve spiders Distina albida and ants like Camponotus sp. Seed treatment with imidacloprid (5 g/kg seed) keeps the crop free of sucking pests over a month.
Apply chemical pesticides only if pest population crosses the ETL. Spray chemicals dimethoate 30 EC or methyl demeton 25 EC @ 500-700 ml/ha when the population reached ETL.
7. Thrips (Thrips Tabaci):
The pest is active from May- September. High temperature with low rainfall favours multiplication.
Nature of Damage:
The nyphms and adults suck sap from the lower surface of leaves lacerating the leaf tissues. The upper side of the older leaves turn brown and the lower side becomes silvery white. Leaves become curled, wrinkled and finally get dried.
Control Measures:
Avoid late sowing of cotton. Grow cowpea/onion/soybean as an intercrop in cotton to reduce early stage pest. Follow deep ploughing in summer and keep weed free field and surroundings. Grow certified acid delinted seeds of tolerant varieties. Removal of alternate host plants like kangni and ambadi. Encourage the activity of parasitoids Thripoctenus briu, Triphleps tantilus and mite Campsid sp. Release Trichogramma Chilonis 1.5 lacs/ha and Chrysoperella grubs @ 1-2 plants.
Release Chrysoperla cornea @ 2 larvae/plant in early stage of the plant and 4 larvae/plant in later stage. Release Cheilomenes sexmaculata @ 1.5 lakh adults/ha at random on crop canopy. Apply NSKE 5% (neem seed kernel extract) to control sucking pests. Apply methyl demton 25 EC @ 1500 ml/ha; or Trizophos 40 EC @ 1500 ml/ha; or dimethoate 30 EC @ 750 ml/ha; or cartap hydrochloride @ 50 SP @ 1000 g/ha; or ethofenprox 10 EC @ 1000 gm/ha.
8. White Fly (Bemisia Tabaci):
The pest occurs throughout the year. Generally infests the crop from November to February. Routinely check all parts of all fields for whiteflies using adult and nymph scouting methods. When populations exceed the thresholds, treat them where needed.
Nature of Damage:
The nymphs and adults feed on the cell sap, reduce the vitality of the plant interfering with normal photosynthesis due to the excretion of honeydew and formation of sooty mold all the over surface of the leaf and lints of opened bolls resulting in process of blackening. Chlortic spots develop on leaves and in severe cases the vein becomes translucent, thickened and in many cases it drops off prematurely. Sooty mold contaminates the lint. The insects help in transmitting and spreading of leaf curl virus disease.
Control Measures:
Avoid late sowing and adopt crop rotation with crop which is not the host of white fly wherever crop rotation is recommended. Grow resistant varieties like K- 2. Cultivate alternate host crops such as tomato, castor, etc. on the boundaries to trap and destroy them.
Set up yellow pan sticky traps at various places at the canopy height in field. Remove and destroy crop residues after last picking. Removal of alternate host plants like kangni and ambadi. Encourage activities of parasitiods like Encarsia shafeei or Eretmocerous mundus.
Release predators such as Chrysoperla Carea or Melachilus Sexaculatus or Coccinella septampunctata, etc. Release Chrysoperla cornea @ 2 larvae/plant in early stage of the plant and 4 larvae/plant in later stage or release Cheilomenes sexmaculata @ 1.5 lakh adults/ha at random on crop canopy.
Spray neem products 1500 ppm. Apply insecticide monocrotophos 36 WSC or quinalphos 25 EC or methyl demeton 25 C or aephate or trizophos or profenophos at fortnightly intervals. The application of synthetic pyrethroids (cypermethrin or decamethrin) be restricted or used in rotation with conventional insecticides. Apply Neem oil + Teepol @3-3.5 litres + 500 ml/ha.
9. Bihar Hairy Caterpillar (Diacrisia obliqua Walker):
This pest is a minor pest. The pest is active during July-November. The adult moths are dull yellow and are profusely covered with hairs, pale buff crimson abdomen with black spots. The caterpillars are gregarious in nature, brownish orange to yellow, 40-45 mm long and with hairy head. Eggs are laid in clusters on the under surface of leaves and pupation takes place in soil or in plant debris in cocoons. The life cycle is completed in 6-12 weeks.
Nature of Damage:
Caterpillars feed on the leaves voraciously and defoliate the plants, leaving only the mid-ribs and veins in severe cases.
Control Measures:
Planting of castor crop along the borders. Collection and destruction of egg masses. Mechanical removal of young larvae, up to 10-14 days of age. Release larval parasite Apanteles diacrisiae. Dust the crop with methyl parathion 2% or Malathion 5% @30 kg/ha or Spray the crop with Chlorpyriphos 20 EC @ @ 1.5 lit/ha or endosulfan 35 EC @1.25 lit/ha.