Cutworms
Noctuidae larvae
Soil-dwelling caterpillars that sever seedlings at the base overnight. Fit cardboard collars around transplants and cultivate before planting to expose larvae.
How to know it
Fat, greasy-looking gray-brown caterpillars 3–4 cm long that curl into a tight C when disturbed. They feed at night and spend the day an inch or two below the soil surface, usually within a hand’s width of the plant they have just felled.
What you'll see
- Seedlings and transplants toppled overnight, cut cleanly through at soil level.
- The severed top left lying beside the stump, uneaten.
- A curled gray caterpillar found by scraping the soil around the base of the casualty.
- A run of losses down a row on successive nights.
- Older plants ring-barked at the base, or lettuce and celery hearts hollowed from below.
Where it comes from
Night-flying moths lay eggs on low plants and weeds in early summer; the caterpillars feed at night for several weeks, growing large enough to sever a stem in one bite, then pupate in the soil. One or two generations a year, overwintering as larvae or pupae in the ground.
Warm dry summers and weedy, uncultivated ground. Newly planted beds and freshly transplanted seedlings take the losses; damage is far heavier on dry soil than wet.
Dealing with it
- Scrape the soil around a felled seedling and you will usually find the culprit within a few centimeters — squash it.
- Fit collars of cardboard tube or plastic bottle around transplants, pushed 2 cm into the soil.
- Water the bed thoroughly: cutworms dislike wet soil and damage drops sharply.
- Hoe and cultivate between rows to expose larvae to birds.
- Water in Steinernema nematodes onto warm moist soil where losses are heavy.
Keeping it out
- Keep beds weed-free through early summer so the moths have nowhere to lay.
- Cultivate ground in autumn and again before planting to expose overwintering larvae.
- Plant sturdy module-raised plants rather than tiny seedlings.
- Encourage ground beetles, frogs, toads and birds — all take cutworms at night.
- Avoid leaving heavy mulch against the stems of new transplants.
What it goes for
Lettuce, brassica transplants, beetroot, sweetcorn, tomatoes, beans and almost any young plant.
Who hunts it for you
- BatsChiroptera A single bat takes hundreds of moths and mosquitoes in a night, and the moths are the parents of your cutworms, corn earworms and hornworms. Put up a bat box on a warm south wall, leave a night-scented corner unlit, and never spray after dark. Grow to recruit it: Evening Primrose,Honeysuckle,Nicotiana,Summer Jasmine
- Beneficial nematodesSteinernema & Heterorhabditis spp. Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
- CentipedesChilopoda Flat, fast, one pair of legs to a segment — and a predator, unlike the slow round millipede it is constantly confused with. It hunts slugs, cutworms, springtails and woodlice by night under mulch and stones. Learn the difference and leave this one alone.
- Frogs & toadsAnura A resident toad works the beds every night for slugs, cutworms, and weevils. Recruit them with water — even a sunken basin pond — plus damp shade and an upturned-pot toad house; skip the slug pellets that poison their prey.
- Ground beetleCarabidae Fast, glossy night hunters that patrol the soil surface for slugs, cutworms, and root-fly larvae. Give them daytime cover — thick perennial edges, stepping stones, a log — and skip the tillage that wrecks their burrows. Grow to recruit it: Lavender,Mint,Thyme
- HedgehogErinaceus europaeus A European animal, and worth saying so plainly: there are no hedgehogs in North America, and the ally that does the same night shift here is the toad, the opossum or the ground beetle. Where they do occur, cut a gap in the fence and skip the pellets.
- Salamanders & newtsCaudata Damp-loving hunters of slugs, worms, woodlice and beetle larvae that spend the day under a log or a stone and work the beds at night. Companions to the toads: they want the same damp shade, the same log pile, and the same absence of slug pellets.
- Snakes & lizardsColubridae & Phrynosomatidae A garter snake works the beds for slugs and voles and a fence lizard clears grasshoppers off a sunny wall. Almost every snake a gardener meets is harmless and useful; give them a log pile, a warm flat stone and a bit of cover and they stay.
- Tachinid flyTachinidae Bristly, house-fly-lookalike parasitoids that lay eggs on caterpillars, beetle grubs, and earwigs — the maggot consumes the host from within. Adults sip nectar from shallow umbels and daisies. Grow to recruit it: Cilantro,Dill,Feverfew,Parsley,Sweet alyssum
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com