Major Insect-pest and their management:-
1. Termites, Odentotermes obesus, Microtermes obesi
Host Range: Polyphagous
Damaging Stage: Adult (Workers)
Identification: Workers are small off-white
Seasonal History: Termites remain active throughout the crop season, but the maximum damage is done during pre-monsoon (May-June) and posts monsoon (September-October) period.
Nature of Damage: At the seedling, stage termites cut the plants from the ground level. The first sign of attack in the young plants is wilting/drying followed by the death of the plant. When the cotton plants are mature, termites construct mud galleries and damage roots and the under a ground portion of the stem; the hollowed portion is filled with the mud. Due to such type of damage, the food supply of the plant is blocked which results in the death of the plant. The termite-damaged plants can be easily pulled out and usually contain termites on them.
Economic Threshold: Ten per cent damaged plants.
- Dig the termatorium and destroy the termite colony.
- Don’t use raw farmyard manure as these encourage the termite infestation.
- Remove the stubbles of the previous crop from the field which attract the termites.
- Seed treatment with chlorpyriphos @10 ml chlorpyriphos +10 ml water per kg seed. Dry the
treated seed in the shade for 30 minutes.
- Use chlorpyriphos @ 2 litres per acre in the standing crop along with irrigation.
2. Leaf hopper: Amrasca biguttula biguttula
Host Range: It is polyphagous. The important host plants are okra, potato, brinjal, and some wild plants like hollyhock, kangi buti, etc.
Damaging Stage: Nymphs and Adults
Identification: Adults are 3 mm long and pale greenish while nymphs are green. Nymphs are found the underside of the leaves during the daytime. Sideways movement is the peculiar characteristic for the identification of the nymphs. Winged adults fly away at the slightest disturbance.
Seasonal History: The pest breeds throughout the year on different hosts but maximum activity in cotton takes place during July-August which increases with the intermittent rainfall.
Nature of Damage: Both nymphs and adults cause damage by sucking the cell sap. The attacked leaves turn pale rusted red. Leaves may turn to cup shape (usually downside) and dry up. In case of severe attack, plant vitality is affected, and cotton bolls may also drop off.
Economic Threshold: Count the leafhopper population on three leaves per plant, one each from the top, middle and bottom. Take observation at least from 10 plants from the field. The population is considered to be at economic threshold, if 2 or more than 2 nymphs per leaf are observed or if 20 per cent of the leaves starts showing yellowing symptoms from the edge of the leaves.
Avoid spraying up to 60 days after sowing the cotton crop as normally the pest does not reach an economic threshold. A low level of infestation by leafhoppers helps in the less damage of American bollworm to some extent. Spray the crop with 250-350 ml dimethoate (Rogor) 30 EC or 300-400 ml oxy-demeton-methyl (Metasystox) 25 EC or formation (Anthio) 25 EC or 40 ml imidacloprid (Confidor) 200 SL, 40 g thiamethoxam (Actara) 25 WG after mixing in 120-150 litre of water.
3. Cotton whitefly, Bemisia tabaci
Host Range: a Polyphagous insect. Some of the hosts are puthkanda, gutpatni, cabbage, cauliflower, sarson, toria, melon, potato, brinjal and okra.
Damaging Stage: Nymphs and adults.
Identification: Adults are 1.0 to 1.5 mm long, yellowish and dusted with white waxy powder. Wings are pure white.
Nymphs: Nymphs are yellowish white.
Seasonal History: The whitefly infestation remains in cotton more or less throughout the cotton season, but the maximum damage in cotton is done during August-September. The Higher population has been noticed in dry weather conditions which encourage its population build up.
Economic Threshold: Average six to eight nymphs per leaf. Count the population from three leaves (one each from the top, middle and bottom) per plant and take an observation at least from 10 plants from the field.
Nature of Damage: Damage is done by sucking the cell sap from the leaves resulting in loss of vitality of the plant. Normal photosynthesis is affected due to the growth of sooty mould on honeydew deposited on the upper surface of the leaves. Consequently, the growth of the plant and yield are affected. Cotton whitefly also transmits the cotton leaf curl virus, and the veins of diseased leaves get thickened becoming cup-shaped (upside).
Spray the crop with 250-350 ml dimethoate (Rogor) 30 EC or 300-400 ml oxydemeton-methyl (Metasystox) 25 EC or formothion (Anthio) 25 EC or 40 ml imidacloprid (Confidor) 200 SL, 40 g thiomethoxam (Actara) 25 WG after mixing in 120-150 litre of water.
4. Mealybugs, Phenacoccus Solenopsis (Homoptera: Pseudococcidae)
Host Range: Congress grass. Kanghi but, Okra, tomato, brinjal, China rose, ber bushes, ornamental plants.
Damaging Stage: Nymphs and adults
Identification: Mealybugs are creamish to grey, soft-bodied, small, oval and cottony in appearance.
Seasonal History: The pest is present throughout the year on one or the other host’s plants. However, it is serious in cotton during July onwards till harvest of the cotton crop. During winter it finds shelter under the stacked cotton sticks and some weeds. As soon as it warms up during March- April, it starts breeding on sprouts of cotton stubbles and congress grass and kanghi buti
Economic Threshold: Sparse population
- All crop residues in previously infested fields should be removed and burnt.
- Field borders should be free from weeds.
- The coccinellid beetles are important predators of mealybug nymphs.
- Spot application of insecticide is advised.
- Spray the cotton crop with the insecticides, thiodicarb @ 1.5 g or profenofos @ 3 ml or quinalphos @ 4ml/litre of water.
- Do not move any plant material with suspected mealybugs. Moving infested plants is the fastest way to spread the pest.
- Do not shake or scatter the infested material.
- Do not spray any chemical insecticide unless mealybug infestation is confirmed; unnecessary spraying may destroy natural enemies which keep mealybug populations under control.
Nature of Damage: Mealybugs damage the cotton crop by sucking a large amount of sap from leaves and stems with the help of piercing/sucking mouthparts, depriving plants of essential nutrients. The excess sap is excreted as honeydew which attracts ants and also develops sooty mould inhibiting the plant’s ability to make food.
5. Spotted bollworm, Earias insulana and Earias vittella
Host Range: Cotton, okra, kangibuti, sonchal, hollyhock, gulkhaira and a few other weeds
Damaging Stage: Larva
Identification: Full grown larvae, E. vittella, are stout, spindle-shaped and light brown with off-white spots on the dorsal surface bearing some hairs on the body. The colour of E. insulana larvae is generally lighter in comparison to E. vittella. Forewings are green in colour in case of E. insulana and off-white strip is present in case of E. vittella.
Seasonal History: The pest remains active throughout the year on one or the other host. In cotton, the damage is done from August to October.
Economic Threshold: During vegetative stage larvae of spotted bollworms damage the shoots. For this, observe at least 30 plants from the one-acre field. If one per cent shoots are found affected, the pest has reached the economic threshold. During the reproductive stage, if 5 per cent fruiting bodies are damaged, the pest has reached an economic threshold.
Nature of Damage: In the vegetative stage larvae bore into the growing shoots, and the affected shoots droop down. Later on, during the reproductive stage, larvae bore into the flower buds, flowers and green bolls consequently shedding of the fruiting bodies takes place. The attacked bolls are tunnelled and blocked with excreta. The infested bolls open prematurely, and the lint is spoiled resulting in lower market value.
The pest can be controlled by adopting the following practices :
- Destroy the alternative host plants mentioned under host range as these serve as a food source. Pest completes its life cycle on these plants and reinfests the cotton in the ensuing crop season.
- If there is an infestation of spotted bollworm at vegetative stage, detopping of the infested vegetative shoots may be done to manage the build-up of the pest population.
- Spray 1.0 litre neem (Achook/Nimbecidin) or 600 ml endosulphan (Endocel/Thiodan/Hildan/ Thiotox) 35 EC or carbaryl (Sevin/Carbavin/Hexavin) 50 WP or fenitrothion (Folithion/ Sumithion/Ekathion) 50 EC or quinalphos (Ekalux) 25 EC or lindane (Kanodane) 20 EC or profenophos (Curacron) 50 EC in150-175 litre of water