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Fall Armyworms in Corn | Biology, Symptoms and Control

Corn/Maize is the world’s highest grain-yielding crop that is affected by fall armyworms attacks. It is crucial for developing nations like Pakistan, where a rapidly growing population has already depleted the available food supplies. After rice and wheat, Corn is the third most significant cereal in Pakistan. It can be crushed to make flour and has a wide variety of uses in both fresh and dry forms. It serves as a source of raw materials for the production of maize starch, oil, syrup, corn flakes, cosmetics, and tanning agents for the leather industry. Present maize production is quite low than its potential but still higher than that of other cereals. The lack of new production technology, along with factors including inadequate cultural practices, low fertility, moisture stress, and insect management techniques are responsible for its low yield.

Insect pests are major issues in the production of maize. The maize crop is frequently attacked by a number of insect pests, including Corn aphids, cutworms, stem/shoot flies, rootworms, and stem borers. Among these factors fall armyworm is a serious constraint which contributes to the low productivity of maize. It is native to the American continent, but due to its strong flying abilities, it has spread to various African and Asian countries. Spodoptera frugiperda, also known as the autumn armyworm, is the main bug responsible for significant losses in maize yield. It belongs to the family Noctuid and orders Lepidoptera. It nourishes on leaves, stems and reproductive parts of the maize plant. It is a polyphagous pest that harms economically significant cereal crops like maize, rice, sorghum, cotton, and different vegetable crops, which has an effect on food security in the long run.

Biology of Fall Armyworms

The four stages of the fall armyworms’ life cycle are the egg, larva, pupa, and adult. The duration of a life cycle varies depending on the season: 30 days in the summer, 60 days in the spring and the fall, and 80 to 90 days in the winter. The autumn armyworm’s egg is dome-shaped, flattened at the base, and bends upward to an apex that is broadly rounded. The egg is roughly 0.3 mm long and 0.4 mm in diameter. Usually, on the underside of leaves, close to the base junction of stem and leaves, the female lays her eggs in clusters of 100 to 200. During the summer, the egg stage lasts just two to three days. Six larval instars are required for the fall armyworm to complete the larval stage. Larvae are initially greenish in colour and then change into orange by the second instar. The length of the larva changes from 1mm in the first instar to 45mm after six instars. The head is reddish-brown speckled with white lateral lines at the fourth and sixth instar. The larval stage typically lasts for 14 days during the summer and 30 days during the cooler months.

Fall Armyworms damage Symptoms

  1. In Corn, it causes most damage at the 3 to 6 leaves stage, when it reaches the protective regions of the whorls. 
  2. They eat the tissue of the leaves, leaving holes behind as a characteristic sign of this insect.
  3. Normally, one or two larvae feed in a whorl, as larger larvae can feed on younger larvae to reduce competition. 
  4. Due to the voracious feeding habits of the larval instars, considerable defoliation and an abundance of the faecal waste left on the plant can be seen at the severe stage.
  5. Crops eventually stop growing and developing, which prevents the formation of cobs and tassels.

How do you control fall armyworms in Corn?

Early detection of pests is necessary before they cause economic damage. Application of control measures is recommended to stop future loss, If 5% of seedlings are cut or 20% of the whorls of tiny plants are infested with fall armyworm in the first 30 days. Effective pest control greatly depends on the timing of the application of treatment.

1. Biological Control

In this method, living natural enemies are used to decrease the number of pests. These methods make use of a variety of biological agents, including pathogens, predictors, and parasites. Wasps from the genus Trichogramma or Telenomus are frequently utilised to decrease autumn armyworm egg populations. Bacillus thuringiensis (Bt), Baculovirus and Beauveria Bassiana are also used as biological control agents against this pest. Some botanical pesticides that are derived from plant or plant extract including neem, marigold flowers, long pepper, and castor have been found to be effective against this pest.

2. Cultural Control

This is a widely used and eco-friendly approach to controlling pests. By planting maize early, you can delay the onset of pests. Utilizing trap crops such as legumes is another method to protect crops from this pest. Prior to planting maize, deep ploughing can expose pupa and larvae to a predictor, which reduces insect infestation. Other cultural practices include weeding, clean cultivation, hand-picking of larvae, and sanitation. Farmers have reportedly utilized a number of natural compounds with success, applying them directly to the whorls of plants. These consist of salts, mud, ash, sand, and lime. Another natural way to control the pest population is by attracting predators and parasitoids. Ants play a significant role as fall armyworms caterpillars’ natural predators.

3. Chemical Control

Synthetic pesticides are used to achieve chemical control, but it includes high cost, contamination of the environment and increase resistance to chemicals. Chemical pesticides are created artificially in such a way that they affect several phases of the pest, hence diminishing its population. Some of the recommended insecticides for fall armyworms are emamectin benzoate (19EC, 200ml/acre), Spinetoram (120SC, 100ml/acre), Bifenthrin (56EC, 300ml/acre), Chlorantraniliprole (20%SC, 50ml/acre), esfenvalerate, chlorpyrifos, malathion, permethrin, etc. However, it is best to avoid using pesticides because they can reduce soil fertility.

Conclusion

The global spread of the fall armyworms is severely reducing agricultural yield. Early maize plantations can delay the onset of pests. In order to detect the existence of pests, proper monitoring should be carried out. If a pest is found, appropriate management techniques should be used. It is important to promote biological, cultural practices, and integrated pest control (IPM).

Shazia Rani

Department of Botany, University of Agriculture Faisalabad

Learn More

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  3. Agriculture Problems in Pakistan | Their Causes and Solutions 
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