Wheat Armyworm Management in Wheat: Symptoms, Treatment, Chemical, Biological, Natural, and Organic Control

Wheat Armyworms, and Mythimna separata are also known as climbing cutworms belonging to the Family Noctuidae of the Order Lepidoptera. They are a type of moth larvae and are considered one of the most destructive pests of wheat since they can cause significant damage during the early stages of crop growth. They feed on foliage, stems, and ears of wheat, resulting in extensive damage to the crop. They feed on both young and mature plants but are more likely to damage young plants due to their smaller size.

In some cases, the damage can be so severe that it renders the crop unmarketable. The most common signs of infestation include large numbers of armyworms on the plants, feeding damage in the form of holes in the leaves and stems, and girdling of the stems. To effectively manage this pest, it is important to understand its life cycle, its preferred habitats, and the best methods for controlling it. This article will provide an overview of armyworms in wheat crops, including their symptoms, identification techniques, and control.

Wheat Armyworm Management in Wheat

Life Cycle of Armyworms in Wheat Crop

The life cycle of armyworms in wheat crops can be broken down into four stages: egg, larva, pupa, and adult. The egg stage of the armyworm is laid in masses on the upper surface of the wheat leaves and can take up to three weeks to hatch. After hatching, the larvae move quickly through the wheat crop, consuming leaves, stems, and heads of the wheat.

The larval stage of the armyworm is also known as a caterpillar, which is the most damaging phase. In this stage, the larvae feed on the wheat crop and can cause significant damage. As the larvae feed, they grow in size and can reach up to 1 – 2 inches in length. After about one month, the larvae will pupate in the soil. The pupal stage of the armyworm is the most vulnerable.

During this stage, the pupae are immobile and can be easily killed by predators or pesticides. The pupae will remain in the soil for about two weeks before emerging as adult moths. The armyworm’s adult moth stage is the life cycle’s final stage. The moths can live up to one month, and they will lay eggs on the upper surface of the wheat leaves, thus repeating the life cycle.

Occurrence of Armyworms in Wheat Field

Location of Wheat Armyworm: Wheat armyworm pest has been reported in wheat crops in many countries, including Somalia, Egypt, Ethiopia, Bangladesh, India, Myanmar, Nepal, Sri Lanka, Brazil, Italy, Australia, the United States, and Mexico.
Host range: Armyworms feed on various crops, including wheat, oats, barley, sugarcane, rice, jowar, bajra, and sorghum.

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Factors Favoring Population Increase of Armyworms in Wheat Fields

Weather – Warmer weather can provide ideal conditions for larvae to thrive and reproduce. In addition, moist conditions can provide the larvae with the moisture needed to survive.
Abundance of food – The presence of weeds and other grasses in the field can supplement as food sources for the larvae.
Field – The insects, like aphids and grasshoppers, may act as hosts for the armyworm larvae, providing them with additional food sources.
Overuse of pesticides – If pesticides are overused, they can kill off natural predators of the armyworm larvae, resulting in a population increase.

Identification of Armyworms in Wheat Field

Egg: The eggs are small, spherical, are laid in clusters of up to 300, and are yellowish-white in color.
Larva: They are greenish-brown and have stripes along their body and a distinctive dark head capsule.
Pupa: The pupae are dark brown and are about the size of a small bean.
Adult: The moths are light greyish-brown in color, with a wingspan of up to two inches.

Damage Symptoms of Armyworms in Wheat Field

The characteristic sign of this pest is the defoliation of the leaves, which occurs because these pests feed on the foliage and stems of wheat plants, causing the plant to wilt, yellow, and eventually die.
They initially consume young foliage and mature foliage, completely skeletonizing the plants.
The fecal particles that the adult larvae expel are rather noticeable.
When a serious attack occurs, complete foliage, including the midrib, is eaten, and the area appears to have been fed on by bovine. The caterpillars move from one area to another while feeding ferociously.
The pest might even consume the awns and young seeds from the ears.

Percentage of Yield Lose in Wheat due to Armyworms

In India, according to the Food and Agriculture Organization of the United Nations (FAO), the armyworm is one of the most destructive pests of wheat in India. It causes losses of up to 70% of the crop in some areas. This can significantly impact people’s food security, reducing the amount of food harvested from the crop.

Cultural Control of Armyworms in Wheat Field

Resistant varieties – The resistant varieties are typically resistant to the toxins the worms produce, making them less attractive to the pests.
Crop rotation – Ideally, a wheat field should be rotated with a non-host crop, such as corn or soybeans, for at least one season. This reduces the concentration of armyworms in the field and helps reduce the severity of any infestation.
Trap crops – Planting trap crops like alyssum or alfalfa, which attract the moths diverting them away from the wheat field, thus, reducing damage.
Fertilizers – Apply appropriate fertilizers at the proper time and in the correct amounts to increase the health of the wheat crop, making it less attractive to pests.
Hand-picking – The pest population can be controlled by hand collecting and destroying the caterpillar larvae.

Biological Control of Armyworms in Wheat Field

Natural enemies of the armyworm include parasitic wasps, lacewings, ladybugs, and predatory beetles. These insects feed on the eggs and larvae of the armyworm, reducing the population and preventing further damage.
Fungi can be sprayed on the crop and the soil, and they will colonize the eggs and larvae of the armyworm, preventing the larvae from developing.

Chemical Control of Armyworms in Wheat Field

Mix 0.5 L of Dichlorvos 85 SL or 3kg of Carbaryl 50 WP or 1 L of Quinalphos 25 EC in 500 Litres of water for one hectare and apply using a knapsack sprayer. These insecticides are typically applied as foliar sprays or as soil treatments.
Bacillus thuringiensis (Bt) is a soil-inhabiting bacterium that occurs in nature, produces a toxin lethal to armyworms, and is most effective when applied before the armyworms have established.
Some insect growth regulators like diflubenzuron and novaluron can be applied as a spray application or soil drench to control the pest.

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Preventive Measures for Control of Armyworms in Wheat Field

Monitoring wheat fields for early signs of armyworm infestations should begin when the crop is at the tillering stage. Look for small, irregular holes on the leaves and the presence of larvae and their excrement on the leaves.
Planting early maturing wheat varieties can help avoid the peak armyworm activity period. Additionally, maintaining the field in a weed-free state can help to reduce the number of available food sources for armyworms.
Plowing the fields in the fall season helps to break up the soil and expose the larvae of the armyworms. This helps to kill the larvae and eggs and reduces the population of armyworms in the fields.

Conclusion

In conclusion, the armyworm pest is a significant threat to wheat crops in many parts of the world. Effective pest management is essential to reduce crop losses and maintain healthy yields. When necessary, integrated pest management should be used to effectively manage the pest, including crop rotation, cultural and physical control measures, and chemical control measures.

Wheat Armyworm Management in Wheat: Symptoms, Treatment, Chemical, Biological, Natural, and Organic Control

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