Cotton
Spiny Bollworm
Earias insulana
Insect
In a Nutshell
- Wilting of terminal shoots before flowering.
- Shedding of squares and bolls.
- Holes in bolls and rotten inside.
- Cotton bolls may gradually become empty.
Cotton
Symptoms
Larvae mainly attack cotton bolls, but might also feed on squares, shoots and flowers. If infested during the vegetative state, they bore through the terminal buds of the shoots and move downward. This causes drying and shedding of terminal shoots before flowering. If the main stem is affected, the whole plant might collapse. When attacked in a later stage, the larvae will bore holes at the base of buds and bolls to feed inside. The tunnel entrance is often blocked by excrement. Damaged flower buds sometimes spread prematurely and so-called flared squares can be observed. Damage to the plant tissue can lead to fungal or bacterial infections. The younger the plant, the more damage the spotted bollworm can cause.
Recommendations
Organic Control
Scouting for eggs or small larvae is essential in the management of this pest. Some parasitoid insects of the family Braconidae, Scelionidae and Trichogrammatidae can be used as a biological control method. Also try predatory insects from the following orders: Coleoptera, Hymenoptera, Hemiptera, and Neuroptera. Make sure to promote these species (or even introduce them to the field), and avoid the use of broad-scale pesticides. You can apply bioinsecticide sprays containing Bacillus thuringiensis to control population peaks. Spray Neem seed kernel extracts (NSKE) 5% or Neem oil (1500ppm) @ 5ml/l.
Chemical Control
Always consider an integrated approach with preventive measures together with biological treatments if available. Treatment is recommended when 10 eggs or five small worms per 100 plants are present during early bloom. As larvae become increasingly resilient to insecticidal treatment while growing, scouting for eggs and young larvae is crucial. Treatment is recommended to be applied during the egg stage. Insecticides containing chlorantraniliprole, emamectin benzoate, flubendiamide, or esfenvalerate can be applied. Chemical treatment may be inviable in low-value crops.
What caused it?
The damage is caused by the larvae of the spiny bollworm, Earias insulana, a common pest in the northern regions of India. Alternative host plants for this pest are, among others, hibiscus and okra. The moths are silver-green to yellow in color, approximately 2 cm long and can be seen on flowers or close to light sources. Three darker streaks can be seen on the wings. Green forms are common during summer while yellow and brownish colors appear in fall. Eggs are of blue in color, singly laid on young shoots, leaves, and squares. The young larvae are light brown with grey to yellow and orange features. They can be best distinguished from most other caterpillars by the tiny spines, visible under a hand lens, that cover most of the body surface. As they reach maturity, they pupate in a silken cocoon attached to leaves or fallen plant parts. Under tropic conditions, a generation is complete within 20-25 days. Low temperatures can delay the process to a length of up to two months.
Preventive Measures
- Plant resilient varieties, if available in your area.
- Avoid monocultures and implement intercropping with beneficial plants.
- Ensure early planting to avoid peak populations.
- Provide uncultivated marginal areas to break life cycle or plant trap crops like hibiscus and okra.
- Leave sufficient distance between plants.
- Monitor the cotton field regularly for larvae and eggs of the spiny bollworm.
- Keep up a sufficient fertilization.
- Promote an early harvest.
- Clear all harvest residues after each cropping cycle.
- Plow deeply to expose pupae to predators and elements.
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