How Armyworm Causes Damage To Maize Plant And How To Control It

Farmers face a lot of challenges during cultivation processes. In crop production, there are two prominent challenges; they are pest and diseases. Pests are very disastrous; they are the carrier of plant diseases and also damage plant parts. Control of pest is very important and has to be treated as cogent as possible.

Armyworm, scientifically known as Spodoptera exempta, is a baleful pest that causes damage to crops in a subtle or unexpected way. This pest has ravaged many cereal farms across the globe, especially maize in the world. It is a global threat to maize production.

Several measures have been put in place to eradicate this pest but seem very difficult to eradicate because the mode at which they operate is very tactical. I implore you to read this article to the last word as it broadly discussed how this pest operates and how you can control them chemically, organically and biologically.

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Armyworm is a subtle and deleterious pest, highly baleful at its larval stage. They are called armyworms because of their ability to invade a farm in large numbers. Armyworm undergoes a complete metamorphosis, that is, it has four stages of growth; namely: embryo, larva, pupa, and imago or adult. The second stage of growth, the larval, often causes a lot of havoc in the farming community, especially cereal crops farms.

The armyworm moths lay their eggs in clusters of 25 or more under the lower leaves or at the base of the plants. The eggs are tiny, globular and greenish white in color. The larva or caterpillar, the most destructive, is a small worm of about 1.5 inches. It has a greenish-brown body with tiny orange colored strips arranges on both sides of its body; the head is usually brown with dark marks.

armyworm pupa

The pupa, practically harmless, is encapsulated in a brown earthen shell and stays below the soil surface. The imago or adult is approximately one (1) inch long with one and half (1.5) inches wingspan. It is usually tan to light brown in color with tiny white spots on each side of the wings.



armyworm damage

As earlier discussed, armyworm undergoes a complete metamorphosis; it has four developmental stages, namely: Embryo, larva, pupa and imago or adult, respectively. Armyworm moths (adult) are ubiquitous but innocuous; they are active during the evening, they hide in grassy vegetation during the day. All they do is to feed on nectars, mate and search for places to lay their eggs (oviposition), usually at the back of host leaves; they lay up to 1000eggs in their lifetime.

Armyworm moths lay their eggs in clusters at the back of their host plant usually grass weeds or cereal crops; after laying, the moth rolls the leaf blade of the plant around the laid eggs. The eggs hatch in about 5-10 days into larvae, the second stage of development.

This larval stage is the most destructive stage; this is where farmers have sleepless nights. The newly hatched larvae, also called caterpillars, are pale green in color and move in a looping motion. They are active at night and feed on the host plants; they feed voraciously on the plants. The armyworm larvae damage the plants by chewing the leaves; they prefer to feed on the succulent leaves in the whorl first, in case of a maize plant. They feed majorly on the leaf margin but in severe invasion, they can devour the whole plant.

armyworm larvae

Towards the end of the third week, the larvae burrow into the soil to pupate, that is, the end of the larval stage and the commencement of the pupa stage. The pupae remain inside the soil for about 7-10 days after which they develop into imago or adult.

The adult, therefore, migrates from their site of emergence to where they lay another set of eggs (oviposition). The adult feeds for about 10 days before the commencement of lay; about 3 generations can emerge in a year. The first generation occurs around March and May, the second generation emerges in July and third generation surfaces late August.



armyworms damage pictures

The second stage of growth is the main threat to farmers as the larvae formed are voracious herbivores. They feed subtly on the leaves; they are not easily noticed. The larvae are about 1 – 1.5 inches long and live for just 3 weeks; they feed on mostly grasses and cereal crops with maize being their favorite.

Their outbreak is more pronounced during the rainy season, especially after a long drought, usually March to April. Their deleterious nature usually makes their outbreak sudden; they show no prior signs, just the damage is seen.

These larvae hid under the plant debris, grass or clogs of soils during the day. You may be thinking of applying any of these maize herbicides to kill the grass weeds since these armyworms love grass plants; believe me, it is more hazardous, if you do. The armyworm larvae become more aggressive; they move directly to your plant, maybe maize or wheat, and damage them up. It is like rendering them homeless, hence, applying herbicides is not advisable.

Armyworm larvae consume leaf tissue and at times, they chew the leaves of small cereals or grains. In severe cases, they may strip the leaf margin and move up to feed on the panicles and floral parts. Armyworm larvae also feed on plants’ flag leaves (a leaf on a cereal plant next to the inflorescence, kernels and succulent stems. Most grains survive moderate armyworm damage if the growing point has not been damaged.

Armyworm larvae infestation on plants is more destructive during the first planting season, usually, March to May. The armyworm larvae live for just 2-3 weeks; their destructive activities take place during this period. They grow up to 1.5inches; during this period, spraying pesticides is not economical because the damage has been done.

However, when they are still below 1 inch, pesticides can be applied to get rid of them but they are not easily noticed at this length. Their activities are not noticed until when they are above 10 days old, over a week; they would have damaged a lot of plants during this period. During this period, their color changes to black. Armyworm has two morphological forms:

  • Gregarious
  • Solitary

The gregarious is characterized by black color with stripes while the solitary has a green color. These two forms are determined by density; at a higher density, they are always gregarious. Their damage occurs at the gregarious form.



Controlling armyworm is very technical because this pest doesn’t show prior signs to their infestation; most times, farmers are always agape at their damage. However, there are practices farmers can implement to reduce the menace of this pest. The following are the ways this pest can be controlled:

  • Planting during the offseason: Offseason is the period at which these pests are inactive and dormant. It is usually during the dry season around October and February. During this period, you can plant without any menace. But you need to supply water in form of irrigation for your plants only.


  • Adopting conventional tillage practice: Armyworm resides in grassy vegetation; they are more rampant when reduced tillage or zero tillage is adopted.  Conventional tillage practice eradicates all grasses and weeds on the field, leaving no room for armyworm moths to lay their eggs. Also, the soil is pulverized such that the moths are exposed to unfavorable condition, thus, expelling the moths and preventing them from laying eggs.


  • Scouting: This is applicable when you adopt a conventional tillage system. This is the close and selective observation done on few plants chosen at random on the field. Look at the ground for armyworm during the day; check the topsoil for armyworm or their black pepper-like droppings littering the ground.


  • Use of organic pesticides: Use neem oil, it is very effective on various stages of the armyworm growth. It repels pests greatly. You can as well use inorganic pesticides but you need to consider the size of the armyworm larvae before applying; apply inorganic pesticides only when the worms are 0.5 inch long, this can be achieved during scouting.


  • Use oil trap: This is done when you place organic oil like groundnut oil in a flat container in the furrow or at the base of your plants. The armyworm moth and larvae get trapped in it, thus, mitigating their destructive effects.


  • Use of beneficial insects to control armyworm: This is called biological pest control. Insects such as lacewing and ladybugs all feed on armyworm eggs as well as the newly hatched larvae. Trichogramma wasps also prey on armyworm; they parasitize any newly laid eggs by inserting their eggs inside the armyworm eggs, thus, killing the armyworm eggs before they hatch into larvae. These insects can be purchased online.


  • Use of beneficial nematodes: Beneficial nematodes like Steinernema feltiae, are soil creatures that disrupt the lifecycle of insects by feeding on each developmental stage, eggs, larvae, and pupae. They are harmless to humans and plants; they feed majorly on armyworm eggs, larvae and pupae found in the soil. They can also be purchased online.


Armyworm damage is a serious threat to cereal production in the world. Its outbreak is becoming more pronounced in the US and African countries. Drastic attention needs to be given to this pest because it can greatly reduce the world production of cereal crops, especially maize.



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