Cutworms
Fat, greyish caterpillars that hide in the soil by day and chew through young seedlings at ground level at night.
Also known as: Cut worms, Agrotis caterpillars
Symptoms and identification
Seedlings and young transplants are found lying on the ground in the morning, cleanly cut through at or just below soil level. Digging lightly around the stem often reveals a plump grey or brown caterpillar curled into a C shape.
Causes
The larvae of several night-flying moths live in the top few centimetres of soil, especially in beds that were weedy or grassy before planting. They are most damaging in the first weeks after sowing or transplanting.
Organic treatment
Search the soil around damaged plants with a torch at night or by scratching at dawn and remove the caterpillars. Water the soil with Bacillus thuringiensis (Bt) or mix neem cake into the bed.
Prevention
Clear weeds and turn the soil a week or two before planting so birds can find the larvae. Protect young transplants with a collar made from a paper cup or plastic bottle pushed 3 cm into the soil.
Chemical treatment (use with care)
In heavy infestations, use a soil insecticide labelled for cutworms on that crop, following the label.