The Fall Armyworm

The attached document transcribed in the following blog post outlines the ever-growing threat of the Fall Armyworm that has invaded the African continent on the economic livelihood of her farmers. By providing thorough descriptions and identification tactics of its varying stages as well as steps towards local and national control, the author’s efforts are a direct function of the issue’s pertinence to Iringa and her surrounding regions.

The most accurately formatted version of the document is provided by clicking the hyperlinked title of the document directly underneath this paragraph: the full text is additionally embedded in this blog post for those unable to download PDF documents.

Fall Armyworm: A Major Threat to Maize Production in African Countries

What is Fall armyworm?

Fall armyworm (FAW), Spodopter frugiperda is an insect of order Lepidoptera. It is one of the most destructive crop pest; and it is the larva stage that damages and destroys different crops; consequently, causing significant economic loss.1,3 This insect is native to the Americas – widely distributed in Eastern and Central North America as well as South America. However, in 2016 it was first reported in Africa that FAW was causing significant damage to maize crop in more than 38 African countries.2,3 Although FAW feeds on over 80 plant species including maize, rice and pastures by feeding on leaves, fruits and grains, it prefers maize. Niassy and Subramanian reported that damage to maize alone in Africa is estimated to be between USD$ 2.5 – 6.2 billion per year.3  It is believed that in Africa, FAW arrived as an invasive species from the Americas as armyworm eggs in imported produce. 2

Description

Fall armyworm undergoes a complete metamorphosis life cycle. Its lifespan, from egg to larva to pupa to moth/adult, lasts between one to three months. I will describe the egg and larva stages in more detail because it is the larva stage that FAW does the most crop damage.3

Egg: eggs are spherical, green in color at the time of oviposition and become light brown prior to eclosion. They are usually laid in masses of approximately 150-200 eggs which are laid in two to four layers deep on the surface of the leaf. The egg mass is usually covered with a protective, felt-like layer of grey-pink scales from the female abdomen. Each female may lay up to 2000 eggs in lifetime. The eggs mature to larvae in 2-3 days at 20-30°C. Larva: Larvae are light green to dark brown with longitudinal stripes. They have eight prolegs and a pair of prolegs on the last abdominal segment. Upon hatching, they are green with black lines and spots, and when they grow, they either remain green or become buff-brown and have black dorsal and spiracular lines. If crowded by a high population density and food shortage the final instar can be almost black in its armyworm phase. Mature larvae are characterized by an inverted Y-shape in yellow on the head, black dorsa pinaculae with long primary setae.3, 4

Identification                                      

Timely recognition and accurate identification of fall armyworm in the field will minimize crop loss. This information will help farmers to recognize the presence of FAW in their field and initiate appropriate control measures.  Half-grown or fully grown caterpillars are the easiest to identify. They have a characteristic pattern of dark pimples (spots) on their backs; each spot has a short bristle (hair). Although the skin looks rough; it is smooth to the touch. On the second to last segment they have four dark spots forming a square. Each of the other body segments also has four spots, but they do not form a square pattern. The head is dark and displays a characteristic upside down Y-shaped pale marking on the front.4

Management and Control of fall armyworm

FAW is one of the most difficult insect pests to control. Therefore, a good understanding of the pest’s behavior is crucial to effective management practice. Control of the FAW have proven quite challenging because they reproduce rapidly and in large numbers, have ability to fly long distance, hide within growing leaves and has been reported to resist several pesticides.2,3 For example, it has been reported that female FAW produce a huge number of eggs – 1500 to 2000 in lifetime. Also, the moths are carried by the wind across long distance – up to 1,000 km. In addition, large FAW larvae consume large amount of leaves tissue but usually active in the morning or late afternoon and in corn, they usually hide deep in the whorl often below a “plug” of yellowish brown frass. This plug protects the larvae from insecticide application, making it difficult to control.2 Because of the ability to hide deep, some recommend that control measures should begin before larvae burrow deep into the whorl or enter ears for more mature plants.1

 Emergency responses by affected African countries have relied on the use of pesticides, but in most cases these measures have proven costly and ineffective.3 Niassy and Subramanian indicated that although the natural approach has been often overlooked, they prove to be effective. Some tactics that are being tested to try and control the fall armyworm in Africa include the use of inter-cropping technology, natural enemies, early warning systems and use of biopesticides.3 More details will be discussed in the following sections.

Prevent, Monitor and Act (PMA) 2, 3,5

I like the use of Acronym (PMA) to summarize the management practises of FAW. In brief, the measures taken involves prevention of FAW outbreak, monitoring presence of FAW in the field, and acting – taking measures to eliminate when present in the field

P – PREVENT

  • Sow at the onset of rains to avoid peak immigration of adults
  • Plant your crops at the same time – avoid having plots of different ages
  • Conserve beneficial insects which kill the armyworms by preserving weeds and flowering plants on the edges of your plot.
  • Intercropping: In this approach crops are grown alongside one another, e.g., intercrop maize with crops such as cassava or yam, which are not attacked by the fall armyworm. Some of these plants act as deterrent to insect pests and weeds. The system has reduced pest infestation drastically. In addition, it may provide high quality fodder for livestock and improve yields and soil fertility.3 Data indicated that when intercropping was adopted in drier areas of Kenya, Tanzania, and Uganda, it reduced the average number of larvae per plant by 82.7% and reduce plant damage per plot by 86.7%3

M – MONITOR

Monitoring and early warnings are crucial to managing FAW outbreak. It will ensure that identification happens very early, before a full outbreak, and will allow for proper response management. Early detection of the infestation is deemed necessary for more effective control, so that if FAW are present in damaging numbers in the field, control measures must be initiated in timely manner while the larvae are still small.

Check your crops in the field weekly once they have emerged for signs of crop damage. Therefore:

  • Eggs: Look for egg masses on the undersides of the leaves.
  • Caterpillars: Look for caterpillars on the undersides of leaves and the whorl. Small larvae cause “window pane or funnelled” leaves. They are light green to dark brown with stripes down their bodies. Large caterpillars have an upside down pale Y-shaped marking on the front and their second-to-last body segment has four dark spots in a square shape.
  • Damage: Look for small light coloured patches and large ragged, elongated holes on the leaves, emerging from the whorl; record how many plants out of 100 are damaged. Consider taking control measures if more than 20 whorls are damaged and caterpillars can be found on plants. Others recommends that control measures should be initiated when egg masses are present on 5% of the plants or when 25% of the plants show damage symptoms and live larvae are still present.2

A – ACT

These are control measures that need to take place when infestation is present is confirmed present in the field as indicated in the above section. These measures are described below.

  • Mechanical control: Farmers need to visit their fields regularly twice a week during the vegetative stage and once a week during later stages. They must handpick and crush or destroy egg masses and young larvae/caterpillars.4
  • Biocontrol: This involves use of biological measures to control FAW population in the field. For example, release of natural enemies such as parasitic wasps which can provide up to 70% control from fall armyworm by laying their eggs on or inside the fall armyworm eggs or larvae. If these natural enemies are reared in bulk, they can be released in huge numbers in affected fields and conserved. As they multiply in the fields, they can control the pest as they feed on the pest’s larvae.3
  • Biopesticides: These are fungal, viral or bacterial based products which kill the fall armyworm. Examples include fungi-like Mearhizium anisopliae or bacterial-base Bacillus thuringiensis that have proven effective against fall armyworm in the US and Brazil.3,4
  • Organic Control: This involves use organic product such as neem-based extract (Azadirachta indica). Farmers in western Kenya reported these organic extract were much more effective in controlling FAW in their field.
  • Local remedies: It has been reported that some farmers in Africa have tried application of ash, lime, sand and soil directly into infested whorls with some success. However, these measures are not as well researched.
  • NB: If you use chemical pesticides, seek advice on which to use from your Agricultural Extension Officer. Spray into the whorl. Ensure you wear long sleeves and trousers along with a mask, goggles, gloves and boots while spraying because chemical pesticides can be toxic. Avoid spraying pesticides early in the crop cycle as this will kill natural enemies that control the pest, and may not be economical.

 

Take Away Facts about fall armyworms

  1. Fall armyworm is a very invasive, destructive pest native to the Americas, but in 2016 it was reported in Africa, and since then, it has spread to more than 38 countries.
  2. It is during the larva (caterpillar) stage that FAW does the most crop damage, as it causes severe damage to over 80 plant species including maize, rice, sorghum and pastures by feeding on leaves, fruits and grains – but mostly prefers maize.
  3. The management of FAW is a complicated due to its ability to reproduce rapidly, fly long distances, resist and hide from insecticide.
  4. Timely and accurate identification of FAW by farmers is important, for the larvae have characteristic features that can easily be identified by farmers. Thus, educating farmers on how to identify a FAW infestation is necessary.
  5. Farmers should employ management measures (PMA) by preventing the spread, monitoring presence in the field, and taking action measures to eliminate FAW.

ABOUT THE AUTHOR:

Ester S.H.M. Mgata has wide range of work experience in Agriculture and Health care. She holds a Bachelor of Science in Agriculture and Master Science in Soil Science and Land Management from Sokoine University of Agriculture, Tanzania. She also holds a Diploma in Medical Office Assistant, Canada and Bachelor of Science in Nursing from the University of Alberta, Canada. In Tanzania, she worked as research officer under the Ministry of Agriculture. She also worked as a Teaching Assistant at Sokoine University of Agriculture. In Canada, Ester has been actively involved in both acute and non-acute settings under the Alberta Health Service. Based on her education and work experience, Ester has a wide range of interests.

 

REFERENCES:

  1. Ric Bessin. Fall armyworm in Corn. Retrieved on July 17, 2018 from:

https://entomology.ca.uky.edu/ef110

  1. Food and Agriculture Organization of United Nations. Fall armyworms. Retrieved July 17, 2018 from: http://www.fao.org/fall-armyworm/en/
  2. Saliou Niassy & Sevgan Subramanian. Exploring the best tactics to combat fall armyworm outbreaks in Africa. Retrieve on July 17, 2018 from: http://theconversation.com/exploring-the-best-tactics-to-combat-fall-armyworm-outbreaks-in-africa-95451
  3. Identification of Fall armyworm. Retrieved from: https://www.cabi.org/search/?q=Fall%20armyworm
  4. Identification of Fall armyworm. Retried July 18, 2018 from: https://www.plantwise.org

 

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