Cutworms are fat brown or grey caterpillars 1-2in long. They are usually found just below the soil surface. Cutworm is a general name for several different kinds of caterpillar, all of which have similar habits. The main pest species in gardens are the larvae of the large, yellow underwing moth, the turnip moth and the heart and dart moth.
Adults emerge from the soil in June or July and almost at once the females begin to lay eggs – on living plants and dead leaves. The eggs hatch within two weeks and the resulting caterpillars feed for a month or two before spinning themselves into cocoons. From these, a second generation of adults emerges in August or September. The autumn cutworm hatching spends the winter in the soil, feeding whenever weather permits, and metamorphoses into adult forms in the following spring.
The different species of cutworms feed between them on a wide range of vegetables and ornamental plants – lettuces, the cabbage family, carrots, celery, beetroot, potatoes, chrysanthemums, dahlias, marigolds – and even on very young trees. The only fruit plants likely to suffer are strawberries. Damage is likely at almost any time of year, but is worst on light soils during dry summers.
Cure is difficult, but prevention relatively easy. Clear away dead plant debris, keep the weeds down, and hoe regularly through the year to expose the creatures to frost and birds. Watch the soil round the plants when you’re out hoeing and you are likely to spot a few of the pests, which can be dealt with there and then. Protect seedlings with insecticidal seed dressings.