Cutworms (soil-dwelling noctuid caterpillars)
Agrotis segetum, Agrotis ipsilon
Role in the garden
Grey, smooth caterpillars of noctuid moths, which live curled up in the soil by day and cut young plants at the collar by night: freshly transplanted lettuces, cabbages and leeks fall as if scythed.
Activity period
May to September, with a peak in early summer
How to attract / manage it
Searching for the caterpillars at the foot of cut plants, protective sleeves, ground beetles, birds, beneficial nematodes.
Practical guide
Where to find them
In the top 5 centimetres of soil, at the foot of attacked plants, especially on loose soils and freshly transplanted beds; the caterpillars curl into a spiral when disturbed.
Prevention
Hoe regularly to expose the caterpillars to birds and ground beetles, keep the soil covered and alive (ground beetles hunt at night), surround young plants with a sleeve (cardboard roll, cut bottle) pushed 2 cm into the ground, water in the evening to make the soil less inviting for egg-laying.
Early signs
A plant cut clean at ground level, sometimes half dragged underground; holes in the lower leaves; a curled grey caterpillar found by scratching at the base.
Action / control
In the evening or early morning, scratch around the cut plants and remove the caterpillar (it stays nearby); water in beneficial nematodes (Steinernema) when the soil is warm and moist; replace lost plants. Bacillus thuringiensis only acts on young exposed caterpillars, of little use here.
Sources
- INRAE, Ephytia : Biocontrol, Agrotis ipsilon et Agrotis segetum (noctuelles terricoles)
- RHS : Cutworms (rhs.org.uk)
- INRAE, Ephytia : Salades, Noctuelles
Favourite plants / resources
Related plant entries
Tomato
Central plant of the tomato guild. The neighbouring basil is reputed to hinder aphids through its volatile compounds.
Carrot
In the vegetable garden, the carrot is planned first and foremost around its pest, the carrot fly, hence the value of interplanting it with onions. Its taproot needs loose, deep, stone-free soil (RHS), without a heavy application of manure just before (GAB/FRAB Bretagne). And when left to flower, this umbellifer opens up umbels that feed hoverflies and other small beneficials, like the other Apiaceae so valued for drawing in pollinators and aphid predators.
Leek
A traditional ally of the carrot: its sulphur compounds are reputed to confuse the carrot fly (Psila rosae), on the model of the onion, whose effect has been measured (Uvah and Coaker, 1984). Earth up during growing to blanch the stem.
Potato
A nightshade with traditional planting (April) or grown under mulch (Charles Dowding) requiring zero earthing-up. Demanding in manure, it readily heads the rotation on an enriched bed (GAB/FRAB Bretagne). Not to follow or precede a tomato on the same bed (shared blight, Phytophthora infestans).