Maize for Silage
Insight 317


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Greasy cutworm (Agrotis ipsilon) occurs throughout New Zealand. Numbers vary greatly from year to year, in some seasons cutworm can reach epidemic proportions, whereas in others they are rarely seen. This bulletin gives descriptions of the various cutworm stages. It outlines the life cycle of the greasy cutworm and methods for its control.


Adult cutworms are brown to greyish mottled moths. They have darker patches on the front wings and have a wingspan of about 50 mm (Fig 1). The female moth is darker than the male. The moths are nocturnal remaining in the vegetation during the day.

Figure 1: Greasy cutworm adult

Eggs are found singly or in clusters. They are about 0.5 mm in diameter. They are pearly white when laid but change to light brown within a day.

Caterpillars are greasy in appearance. They range in colour from light grey to dark brown-black and have two yellow dotted strips running down the back. Fully grown caterpillars are up to 50 mm long (Fig 2). During the day they may be found curled up in burrows 25 - 50 mm below the soil surface.

Figure 2: Greasy cutworm larva

Pupae are reddish brown and are found in the soil. 


Most greasy cutworm overwinter in the soil as pupae, however some moths are present throughout the year and larvae are found in warmer regions. Growth and development occur once the temperatures exceed 10.4° Celsius. Female moths mate and begin egg laying within a few days of emergence. Each one deposits between 20 and 2,000 (generally 600 to 800) eggs on vegetation, open ground or in cracks in the ground. Eggs hatch after 3 - 7 days.

The caterpillars feed on a wide range of plants. Small caterpillars live and forage amongst the leaves while larger caterpillars live in burrows in the soil emerging at night to feed. Large caterpillars feed at the base of plants usually severing the stem.

The larvae live in the field for 2 - 20 weeks depending on the amount of available feed. They pupate and the moths emerge after 2 - 4 weeks. There are three generations of cutworm per year in warmer areas but only two generations in cooler regions. Summer generations take 9 - 10 weeks to grow from egg to mature cutworm.


Maize seedlings are most vulnerable up to the four leaf stage. Damage often begins before seedling emergence. Larvae which are present before the maize plants emerge are the main problem as plants are normally too large to be killed by the later hatching eggs. The severity of crop damage depends on the number and size of the caterpillars present.  Worst damage occurs when high numbers of large caterpillars are present at seedling emergence. A single caterpillar can destroy up to four plants. Plant damage and decreases in plant populations can be high in severe infestations.

In emerged seedlings greasy cutworm damage is characterised by plants that have been "cut" off.  The plants are severed around ground level. Frequently parts of these plants are dragged underground and eaten over a period of several days. Plants that are cut off below the growing point are killed, while plants cut above the growing point may recover but often have reduced yields. To locate the caterpillar, an area about 75 mm around a damaged plant should be excavated to a depth of 60 mm. Caterpillars can also tunnel into the stems. A smooth edged hole some 5 - 10 mm in diameter will be clearly visible near the base of the stem.

Infestations can occur once the crop has reached row cover stage, but usually only in crops where the control of weeds has been poor. The brace roots or parts of the stem base may be eaten and while this may not affect the plant immediately, it can result in plant lodging (falling over) at a later date.


The amount of weeds in a paddock before planting has a major effect on the number of eggs that are laid. Weedy patches also allow caterpillars to survive and carryover until the maize crop emerges. Ideally a 5 - 6 week weed-free fallow period should be achieved before planting however this is seldom practical.

The best control option is to plant Poncho® insecticide treated seed Poncho® also controls Argentine stem weevil and black beetle. It has a withholding period of 42 days. A small amount of plant damage may be seen in Poncho® treated crops since large cutworms may ingest the odd plant before they consume a lethal dose of insecticide.

Pioneer Premium Seed Treatment® offers a number of industry-leading insecticide options to protect your crop from insect damage. To carry the Pioneer Premium Seed Treatment stamp of approval. Every bag of Pioneer® brand maize seed must meet stringent quality control standards which ensure the precise dose of seed treatment is applied to each and every seed. For your protection every bag of Pioneer® brand seed is mechanically stitched closed with green and white bi-colour tamper proof string. This locks- in the Pioneer warranty and Seed Replant Risk Cover and guarantees there are a minimum of 80,000 kernels in each and every bag.

Check your crop regularly. Cutworm damage is most likely to occur prior to the 4-leaf stage. Remember that weed control is often less effective in wet areas of the paddock and cutworm infestations are most likely to start there. If Poncho® is not used and cutworm damage is visible, an insecticide spray is highly recommended. Sprays should ideally be banded onto the rows. Use of high water rates improves penetration particularly if the chemical can run off the plant and concentrate around the base. Since caterpillars feed at night, sprays are best applied in the evening. Avoid spraying in hot, dry and sunny conditions as there is little chemical penetration. There are a number of insecticide sprays that can be used to control cutworm. Consult your merchant or Pioneer representative for crop specific advice.

Insecticides that are used for greasy cutworm control are toxic. Care should be taken in handling and applying them. Remember that most insecticides have withholding periods and these should be adhered to.


Greasy Cutworm in Maize and Sweetcorn Biology, Damage and Control (1981) Aglink FPP 514, MAF

New Zealand Pests and Beneficial Insects (1984) Scott, R.R (Ed) Lincoln University

The advice of Paul Addison (AgResearch Ruakura) in the preparation of this bulletin is gratefully acknowledged.

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The information in this publication is general in nature only. Although the information in this publication is believed to be accurate, no liability (whether as a result of negligence or otherwise) is accepted for any loss of any kind that may arise from actions based on the contents of this publication.

© 2021, Genetic Technologies Limited. No part of this publication can be reproduced without prior written consent from Genetic Technologies Limited.

Revised: June 2015
Expires: June 2018