Initial symptoms are characterized by a silken web that wraps around the leaves. Feeding damage can be seen on leaves, leaving them skeletonized. The inner leaves of cabbages are often damaged. They feed on flower buds and also leave boreholes in pods. Excreta of caterpillars will be left over the leaves and hearts of cabbages. The eggs can be found on the lower side of the leaves. The health of the affected plants gets deteriorated due to the leaf damage.
Damage is caused by the larvae of Crocidolomia binotalis. The larvae rarely attack seedlings but feed on all stages of the plants. Eggs are laid on the lower side of the outer leaves in clusters of 40 to 100. They appear pale green at first, and later become bright yellow and brown just before hatching. Newly hatched caterpillar larvae are about 2 mm long and they grow up to 20 mm with long hairs when mature. In the later stages, they make thick webs over the leaves and the caterpillars feed beneath them. Moths are usually active during the night, and can infest the crops from early stages up to harvest period. It also infests radish, mustard, turnip and other crucifers. The excreta make the vegetable inconsumable.
Use Bacillus thuringiensis as soon as the damage is seen (should be applied in the evening). Thoroughly cover the plants by careful spraying as the scope is to kill the caterpillars by making them consume the insecticide. The eggs are not susceptible to Bt, but small larvae are more susceptible than the fully grown ones. Use fresh neem, lemongrass, ginger or other botanical pesticides @ 1 lit / 15 lit of water.
Always consider an integrated approach with preventive measures together with biological treatments, if available. Avoid using broad spectrum insecticides (such as pyrethroids and organophosphates) as they will kill the natural predators. Spray insecticides, such as Phosalone, Fenvalerate, Cypermethrin or Deltamethrin. Do not repeat the insecticides with a similar mode of action.