Caterpillars can very quickly cause considerable damage to crops, particularly brassicas. They are the larval stage of butterflies and moths - on brassicas, normally the large white (Pieris brassicae) , the the small white (Pieris rapae) or the cabbage moth (Mamestra brassicae).
SymptomsAside from the caterpillars themselves which reach 3-4cm in length and can be very numerous:
- Yellow eggs on the undersides of leaves
- Holes in leaves
- Dark droppings at the base of leaves where they collect
Prevention & control
- Netting will physically prevent attacks but make sure it's held well away from leaves to prevent laying eggs through the netting
- Encourage natural predators such as wasps
- Look for and crush any eggs on the underside of leaves
- Once holes appear, pick off the caterpillars - those of the small white butterfly are green and can be difficult to spot as they lie along the leaf veins.
- In serious cases:
- Spray with Bacillus thuringiensis
- Spray with pyrethrum
- Apply a nematode treatment