Ravinder Singh Chandi and Vijay Kumar
Cotton is an important Kharif crop of Punjab. Apart from its value as a fiber, it has great potential to use as edible oil. Many factors are responsible for low productivity and production but the magnitude of insect pests that damage cotton crop from sowing to maturity is most important. Cotton ecosystem harbors a wide variety of arthropods and consequently requires a constant protection from insect pests. The introduction of Bt cotton helped in the management of bollworms and tobacco caterpillar but do not provide effective control of sucking pests. Last year whitefly played havoc with the cotton crop. It damages the plants directly by depriving the host plants of their nourishment, because both nymphs and adults suck the plant sap by feeding on the under surface of leaves and excrete honey dew which provides substrate for development of sooty mould which blackens the leaf and lint. It also causes stunting of plants, bad boll opening and poor quality of lint. The attack of whitefly gives the plant a sickly appearance. Besides cotton it also attacks several crops like brinjal, tomato, chillies, potato, cucurbits (cucumber, long melon, summer squash etc.), moong, mash, soybean and several other weed hosts like peeli buti, kanghi buti, puthkanda, button weed, bhang, makoh etc. Female lays eggs on the lower surface of leaf. Nymphs are oval, light yellow and in fourth instar, the red eyes become conspicuous. Except the first instar all other instars are immobile and remain attached to the under surface of leaves. The body of adult is covered with white waxy powder. It completes 8-10 generations in a year. Whitefly also transmits deadly cotton leaf curl virus.
Monitoring and surveillance: Regular monitoring is effective strategy for the management of whitefly on cotton as it helps in forecasting the outbreak of a pest. Surveillance is mandatory for application of control measures against whitefly. Field should be examined at least twice a week to collect information pertaining to its incidence. For whitefly, count of adults should be made from 3 fully formed leaves in the upper canopy before 10 a.m. Damage symptoms should be recorded as appearance of honey dew on 100 plants. For whitefly economic threshold level is 6 adults per leaf or appearance of honey dew on 50 per cent plants.
Management: For effective management of whitefly, follow the integrated pest management strategies as given below:
Grow only recommended cotton cultivars and complete the sowing up to 15th May
Timely sowing, judicious use of fertilizers, irrigation, proper spacing and clean cultivation will prevent the early build up of whitefly and helps in conserving the natural enemies
Prefer to grow desi cotton in areas of high infestation of whitefly
Do not grow alternate crops like okra, moong and arhar in cotton crop and as border rows in order to reduce the incidence of whitefly
Eradication of weeds like kanghi buti, peeli buti, puth kanda, dhatura, congress grass, wild sunflower etc on field bunds, wastelands, roadsides and irrigation channels/canals as these are suitable hosts for whitefly
Whitefly also attacks other alternate host plants like brinjal, cucumber, summer squash, long melon, squash melon, potato, tomato, chilli, okra, moon, mash. Regular surveillance should be done for timely management on these crops
Regular monitoring is effective strategy for the management of whitefly in cotton
First one or two sprays with neem based insecticides like Nimbecidine/Achook @ 1 litre/acre in 125-150 litres of water should be done to manage initial infestation of whitefly and to conserve natural enemies
Decision regarding spray of insecticides should be taken based on economic threshold level. If population of whitefly reached 6 adults per leaf or more before 10 a.m. spray the crop
When adult population is more spray the crop with 80 g Ulala 50WP (flonicamid) or 200 g Polo/Craze/Ruby/Ludo/Shoku 50WP (diafenthiuron) or 800 ml Fosmite/E-mite/Volthion/Gold mit 50EC (ethion) or 600 ml Marktriazo/Sutathion 40EC (triazophos) per acre
When nymph population on the under surface of leaves is high spray with 500 ml Lano 10EC (pyriproxyfen) or 200 ml Oberon 240SC (spiromesifen) in 125-150 litres of water/acre
Do not mix recommended insecticides with other insecticides, use only proper dose of recommended insecticide and do not repeat insecticide of same group in subsequent sprays
Avoid using synthetic pyrethroids (cypermethrin, fenvalerate, deltamethrin), acephate and Pride (acetamiprid) to minimize resurgence of whitefly
Spray technology: For proper management of whitefly method of application plays a significant role. Effective use of insecticides also depends upon the spray pattern of the insecticides. The insecticides should be sprayed using 125-150 litres of spray material per acre with manually operated knapsack sprayer or 75 litres with shoulder mounted power sprayer and tractor mounted sprayer or 12-15 litres of spray material per acre by using backpack type air-assisted electrostatic sprayer or 300-400 litres of spray material per acre by using auto rotate gun type sprayer or 250-400 litres of spray material per acre by using PAU multipurpose high clearance sprayer. For effective spraying on cotton make pathways at 2 meters distance for manually operated knapsack sprayer and at 4 meters for shoulder mounted power sprayer. While using tractor mounted boom sprayer, farmers should keep the gap according to wheels of tractor and use the same tyre tracks and run the tractor in the same direction for all sprays. It should have 13 hollow cone nozzles fixed on a boom, at a distance of 75 cm from each other. For spraying against whitefly the speed of tractor should be 4 km per hour. Keep the spray booms about 50 cm above crop canopy.