Eighth week- Use low cost yellow sticky traps @ 40 per acre during initial phase of cotton crop to check early infestation of whitefly, irrigation should be given to the crop at this stage to promote good establishment of crop.
Whiteflies
Description of Insect Stages
Eggs are yellowish white laid singly on the under surface of leaves. They are stalked and sub elliptical in shape. Nymphs are yellowish and brownish, sub elliptical and scale like. They are found in large numbers on underside of leaves. Pupae also resemble nymphs in shape and have brownish opercula. Adults are tiny and white in color. They have a yellow body dusted lightly with a white waxy powder. Females are 1.1 –1.2 mm long; males are slightly smaller. Antennae of females are longer than males. Hind legs are larger than anterior pair of legs. Large numbers of adults are found in middle region of the plant.
Nature of Damage and Symptoms
Whiteflies cause damage to cotton plants in two ways firstly by sucking the sap and secondly by excreting honey dew on which sooty mould grows. Damage from direct feeding reduces the photosynthetic activities of the plant and hence the yield. Indirect damage results from lint contamination with honeydew and associated fungi and through transmission of leaf curl virus disease. Late season severity affects the seed development and the lint quality. Leaves curl upwards and the plant vigour reduces. Leaves become shiny with honeydew or darkened by sooty mould growing on honeydew. Lint contamination with honeydew and associated fungi occur during heavy infestations after boll opening.
Life History
The female whitefly lays the eggs singly on the under surface of leaves and mostly on the top and middle crop canopy. Each female is capable of laying about 120 eggs. The incubation period varies from 3-5 days during spring and summer, 5-17 during autumn and >30 days during winter. The nymphs after hatching fix themselves to the underside of the leaves and they moult thrice before pupation. The nymphal period varies from 9-14 days during summer, and 17-19 days during winter. The pupal period is 2-8 days. The total life-cycle ranges from 14 to 107 days depending upon the weather conditions. There are about 12 overlapping generations in a year and the pest also reproduces parthenogenetically at times. Whiteflies have extremely wide host range.
Management of whiteflies
- Avoid late sowing and excessive use of “N” fertilizers.
- Destroy infected shoots during early stages.
- Release predators like Coccinellids or Chrysoperla carnea.
- Any of the following insecticide can be used: 0.05% oxyedemeton methyl 25 EC, 0.02% dimethoate 30 EC, 0.02% acephate, 75 SP or 0.005% 1 of imidachlorpid 17.8 SL.
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