You go out in the morning to the field where you planted tomato or pepper seedlings a few days ago, and you find some of them lying on the ground as if someone had snipped them with scissors right at soil level. The leaves are intact, the stem is cleanly cut, and there is no sign of any insect nearby.
This puzzling scene is the well-known signature of the cutworm, the larvae of night-flying moths of the genus Agrotis. The best known are the black cutworm (Agrotis ipsilon), found in most regions of the world, and the common cutworm or turnip moth (Agrotis segetum), found in Europe, Asia, and Africa.
Pest: Gray or brown night-active larvae that curl into a C shape under the soil and come out at night to cut seedlings.
Damage: Seedlings cut at soil level and left lying, with no wilting or rot.
Detection: Dig in the soil near the cut seedlings to find the larva, and scout the field after sunset.
Common mistake: Treating the plant with a fungicide on the assumption that the problem is a disease, when the culprit is a larva feeding at night.
Rule: Protective collars around the stem, a clean field, and a suitable bait in the evening protect seedlings from nighttime cutting.
Cutworm Overview
The cutworm does not need large numbers to hurt you. A single larva can cut several seedlings over successive nights. The danger is usually concentrated in a short period after planting or emergence, but it is a decisive one: every seedling lost means a gap in the row, or replanting and a delay in the season.
The black moth in particular is a strong migrant, and its numbers may arrive on air currents at the start of the season. Among the main crops it attacks:
- Transplanted vegetables: Tomato, pepper, eggplant, cabbage, cauliflower, lettuce, and onion.
- Field crops: Corn, cotton, tobacco, beets, and sunflower.
- Tubers and roots: Potato, carrot, and turnip.
- Lawns and nurseries: In addition to dozens of broadleaf weeds on which the larvae begin their lives.
Signs of Damage: What to Look For
Cutworm damage differs between small and large larvae, and takes a different form in each crop. The golden rule: do not just look above the soil, look beneath it.
By Larval Age
- Small larvae (early instars): They stay above the soil surface and feed on lower leaves and weeds, making small holes or scraping that may go unnoticed.
- Large larvae (fourth instar and up): They hide in the soil during the day and come out at night, cutting seedlings at or just below soil level and moving from plant to plant over successive nights. Sometimes they drag part of the cut plant into their burrow.
By Crop
- Transplanted seedlings: A clean cut at the base of the stem, especially in the first weeks after transplanting.
- Corn: The whole seedling cut, or a hole bored into the stem below the soil surface so the top wilts and dies. A plant whose stem has thickened is less likely to be cut through completely.
- Potato and root crops: Holes and cavities in tubers and roots near the surface, lowering their market value and opening the door to rots.
- Lawns: Small patches of grass chewed near the soil, with small holes that are the tunnel entrances.
- Nurseries: They can wipe out entire seedling trays in one night.
Check for Yourself: Dig in the Soil
Choose a freshly cut seedling and dig around its base in a circle with a radius of about 10 cm and a depth of about 5 cm. You will usually find a larva curled in a ring or C shape, gray or glossy dark. Finding it next to the seedling settles the diagnosis.
If instead you find a fat, creamy-white C-shaped larva with a brown head and clear legs that eats roots so the plant wilts gradually, that is a white grub, the larva of scarab beetles, and it has a different program that you can find in the Pest Library.
Life Cycle and Appearance
The cycle is completed in warm weather in about 5 to 8 weeks, and there are multiple generations a year (up to three or four or more in hot regions).
Egg
- Shape: Small and round, about 0.5 mm across, with fine ribs, white when laid and darkening to brown just before hatching.
- Where laid: Singly or in small groups on low weeds and plant debris, and sometimes on moist soil.
- Number: A female may lay a thousand eggs or more during her life.
- Hatching: Hatch in about 3 to 6 days depending on temperature.
Larva
- Duration: Usually passes through six to seven larval instars over about 3 to 5 weeks.
- Size: Fully grown, about 4 to 5 cm long.
- Color: Gray to dark brown or almost black. The skin is smooth and glossy, looking greasy in the black cutworm, with clear black breathing spiracles on the sides.
- Distinguishing sign: It curls into a ring or C shape as soon as it is touched, and lives during the day in the soil at depths of up to about 10 cm.
Pupa
- Where it pupates: In the soil, inside an earthen cell a few centimeters deep.
- Shape: A glossy reddish-brown pupa about 1.7 to 2.5 cm long.
- Duration: About two weeks in warm weather.
Adult Moth
- Size: A wingspan of about 4 to 5.5 cm in the black cutworm.
- Wings: The forewing is dark brown, and in A. ipsilon a small black dagger-shaped mark appears near the kidney-shaped spot, which gave it its scientific name. The hind wing is pale grayish white.
- /strong> Active at night and attracted to light, laying eggs on ground covered with weeds.
Here is the most important practical piece of information: land left full of weeds before planting becomes a nursery. The larvae hatch and feed on the weeds, then you plow the weeds under or spray them with a herbicide, and nothing is left for the hungry larvae except your new seedlings.
Monitoring and Non-Chemical Solutions First
Start scouting from the first day after emergence or transplanting, preferably in the morning when the night damage is fresh. Walk through several locations in the field and count plants that are cut or wilted at the base.
In corn, some guidelines use a threshold of a certain percentage of cut plants together with active small larvae as the signal to intervene. In high-value transplanted vegetables the threshold is much lower, because each seedling is costly.
Monitoring tools include wooden boards or damp burlap sacks placed on the soil in the evening and lifted in the morning to find the larvae under them, and pheromone and light traps for the moths that warn you of a new wave arriving. These are the most important non-chemical solutions that protect seedlings:
- Protective collars around the stem: A ring of cardboard, plastic, or a can with both ends cut off, pushed around the seedling after transplanting so that part of it is below the soil. Very effective in gardens and small areas.
- Hand picking: Dig in the morning around cut seedlings and destroy the larvae.
- Natural enemies: Ground beetles, birds, parasitic wasps, and parasitic flies.
- Entomopathogenic nematodes: Of the genera Steinernema and Heterorhabditis, used commercially against soil larvae, and they need moist soil.
- Bt bacteria: In baits or sprayed on small larvae.
Chemical Control: In the Evening and at the Base
The cutworm is not on the leaves during the day, so ordinary spraying on the foliage is mostly wasted. Successful spraying against it has three features:
- In the evening or before sunset: So the pesticide is fresh when the larva comes out.
- Directed at the base of the plant and the soil around it: There is no point in covering the upper leaves well and leaving the cutting zone untreated.
- With suitable soil moisture: Larvae come near the surface in moist soil, and a light irrigation before treatment may help.
One traditional method that works well is the poison bait: bran with an attractant such as molasses and a pesticide registered for this purpose, scattered in the evening around the plants. The larva prefers the bait, eats it, and dies.
On rotation: unlike cotton leafworm and bollworms, resistance in the cutworm is much less common, so pyrethroids (Group 3A) usually remain effective on it if applied in the right place and at the right time.
Even so, rotation remains good practice, especially if the field has other caterpillars treated with the same products. Groups in use include 3A (such as lambda-cyhalothrin and bifenthrin) and 28 (such as chlorantraniliprole).
Suitable Products From Our Store
At Orkida Agricultural, for the cutworm we choose pesticides that stay put on the soil surface where the larva feeds, with an alternative from a different group and a sprayer that helps you direct the spray to the base:
- Brigadier 200 SC: bifenthrin with imidacloprid. Bifenthrin is a pyrethroid that stays on the soil surface and kills the cutworm on contact when it comes out to feed at night. We spray it in the evening, directed at the base of the plants and the soil around them.
- Warrior 10 CS: lambda-cyhalothrin (Group 3A) in a slow-release capsule formulation that extends its effect on the leaves and soil surface, so it reaches caterpillars as they feed on corn, wheat, and vegetables. Suitable for field crops and open-field vegetables.
- Coragen 20 SC: chlorantraniliprole (Group 28) for lepidopteran larvae in general. It gives you an alternative from a different group than the pyrethroids, and helps if there are other leaf-feeding caterpillars in the field.
- Eco Spray 20-Liter Backpack Sprayer, Ultra Model: with its multiple nozzles, it lets you narrow the spray and direct it to the base of the seedlings instead of the leaves.
Doses and pre-harvest intervals follow the label of each product and the treated crop.
Prevention and Farming Practices
Most cutworm infestations are made before planting, in the way the land is prepared. These practices cut the pest off early:
- Clear the land of weeds at least two weeks before planting: Not on the day of planting itself, so the small larvae starve before your seedlings arrive.
- Plow and turn the soil: Before planting, it exposes larvae and pupae to the sun and birds.
- Watch high-risk land: Former pastures, land that was alfalfa or neglected, and low-lying wet land.
- Strong seedlings: A seedling with a thicker stem tolerates more and gets past the danger stage faster.
- Remove the previous crop's residues: They attract moths to lay eggs.
- Regular morning scouting: In the first three weeks after transplanting or emergence.
Frequently Asked Questions
Why do I find seedlings cut but see no insect?
Because the cutworm feeds at night and hides during the day in the soil near the cut plant. Dig around the base of the seedling to a depth of a few centimeters and you will usually find it curled up.
When is the best time to spray for cutworm?
In the evening or before sunset, directing the spray at the base of the plant and the soil surface around it.
Do weeds increase cutworm infestation?
Yes. Moths lay eggs on weeds and weedy ground, and the larvae begin on them and then move to your seedlings. Clear the land at least two weeks before planting.
What is the difference between a cutworm and a white grub?
The cutworm is a larva of a moth, gray or dark and glossy, which cuts the stem at soil level. The white grub is creamy white, C-shaped, with a brown head and clear legs, and it eats roots underground.
Are poison baits effective?
Yes, baits made of bran, an attractant, and a pesticide are a traditional and effective method, especially if scattered in the evening on moist soil around the plants.
How long do seedlings stay at risk?
The greatest danger is in the first weeks after transplanting or emergence. Once the stem thickens, the risk of complete cutting falls, although larvae may continue feeding on lower leaves or tubers.