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Fall armyworm

Crop

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How important is it?

On this page, our attention is focused on Fall armyworm in Africa which is an invasive species. Fall Armyworm is considered a major problem because of its cause a severe economic loss on major food crops worldwide. Although much more data is needed one estimate by CABI (CABI 2017) estimated losses lying between US$2,481m and US$6,187m per year. FAW is particularly problematic also because it can occur on many important crops besides maize, such as sorghum, rice, and sugarcane.

 

How is it identified?

The damage may vary depending on the stage of the crop, insect population, and stage of larvae, etc. Though the damage can be easily identified by characteristic scrapping (caused by first and second instar larvae-Fig 1) and holes on the leaves (caused by third to sixth instar larvae- Fig 2). Sometime may cut the leaf in half, resulting in a reduction of photosynthetic leaf area (Fig 3). The damage gives the ragged appearance to the plant. The larvae are nocturnal in habit. They are active and feed only during the night. They hide in leaf whorl during the daytime.

 

 

           Fig 1: Scraping damage caused by early instar larvae

                   Fig 1: Scraping damage       

 

 Fig 2: Elongated holes on corn leaves caused by late instar larvae

    Fig 2: Elongated holes     

         

     Fig 3: Ragged appearance of plants due to late instar larvae

        Fig 3: Ragged appearance          

        

            Fig 4: Late instar larvae feeding on cob

                Fig 4: Cob damage 

      Fig 5: Injury to corn plant at whorl stage

               Fig 5: Whorl injury  

What else it could be?

Plant parts

Fall armyworm (FAW)

African armyworm (AAW)

Corn earworm (CEW)

Western bean cutworm (WBC)

Common armyworm or true armyworm (AW)

African Maize Stalk Borer

Leaf whorl

Window pane symptom

Window pane symptom

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Window pane symptom

Leaf

Elongated holes

Starting at the margins and moving inwards, leaving the leaves with a ragged appearance

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Larvae initially skeletonize foliage, but by the third instar they eat holes in leaves and soon afterward consume entire leaves

Elongated holes

Stem

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Internal feeding

Tassel

Discoloration of panicle

Discoloration of panicle

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Feeds on anthers

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Discoloration of panicle

Cob

Boreholes on husk and feeds on developing grains

Boreholes on husk and feeds on

Boreholes on husk and feeds on silk and grain

Boreholes and feeds on silk and grain

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Tunnel into maize cobs

 

What is it?

The fall armyworm, Spodoptera frugiperda belong to order Lepidoptera and family Noctuidae. The life cycle of FAW involves an egg, larva, pupa and adult moth (Fig 12). The main destructive stage is a larva. Generally, female moth lays 100-200 eggs in a mass on the lower surface of the leaves, but sometimes can also found on the upper surface. Eggs will hatch in 1 to 3 days. The first and second instar larvae feed on corn leaves by scraping the leaf surface. Whereas, the third to sixth instar larvae feed on leaves by making elongated holes. The larval stage lasts for 9 to 20 days, after which the mature larvae fall off and burrow into the soil and pupate inside the cocoon. Within 8 to 10 days adult moth will emerge from the pupa.

What crop does it eat?

FAW has a wide host range but at present, it becomes a major problem in African continent mainly on corn, rice, sorghum, sugarcane, wheat, and millets. It also prefers to feed on cowpea, peanuts, potato, soybean, and cotton. It is considered a polyphgagous pest meaning it easts many different types of food plant. 

How do I recognize it?

Fras: The presence of moist sawdust-like frass near the funnel and upper leaves (Fig 6).

Larvae: Larvae undergoes six developmental stages (called instars). The first and second instar larvae are green in color with a black head (Fig 7). The third to sixth instars larvae are light tan to tan, green in color with white visible strips on the body (Fig 8). Also, these stages have distinct four dark spots arranged in a square on 8th and 9th abdominal segments (Fig 8).

Egg: Eggs are laid in masses. Each mass may contain 100 -200 eggs and covered with grayish cottony scales and tiny bristles (Fig 10).

Adult moth: Both male and female moths are 30 to 40 mm from wing tip to wing tip (Fig 11). The hind wings of both sexes are white/silver with a narrow dark brown border. The forewing of male moths is having more patterns and a distinct white spot on the outer tip.

             Fig 6: Appearance of moist sawdust-like frass near the funnel and upper leaves

           Fig 6: Saw-dust like frass  

        Fig 7: Early instar larvae of fall armyworm

           Fig 7: Early instar larvae  

   Fig 8: Late instar larvae of fall armyworm

Fig 8: Late instar larvae 

             Fig 9: Distinct four dark spots arranged in a square on 8th & 9th abdominal segments 

             Fig 9: Distinct four dark spots  

        Fig 10: Egg mass of FAW on the upper surface of corn leaf 

      Fig 10: Egg mass  

   Fig 11: Adult moth of fall armyworm

Fig 11: Adult moth  

            Fig 12: Life cycle of fall  armyworm

                       Fig 12: FAW Lifecycle ​​​​​​​    

        Fig 13: A. Corn earworm (Helicoverpa armigera) larvae, B. African armyworm (Spodoptera exempta) larvae, C. Common/true armyworm (Mythimna unipuncta), D. Beet armyworm (Spodoptera exigua) larvae.

              Fig 13: Other pests of maize​​​​​​​

Where does it occur?

FAW  originated from tropical and subtropical regions of the Americas (North and South America). It is now a serious pest in West, Central, and Southern Africa. On this page, we will attempt to provide an update on country records. 

South Africa       

         Malawi      Angola       Niger       Benin     Sao Tome and Principe

Tanzania 

        Ethiopia      Rwanda      Nigeria       Togo      Democratic Republic of the Congo        

Kenya

        Mozambique        Burundi            South Sudan       Namibia

     Republic of the Congo 

Uganda

        Zimbabwe      Cameroon      Guinea       Chad

      Ghana

Swaziland

        Botswana      Zambia      Burkina Faso             

Management

Field Scouting: Survey the field regularly and look for egg mass, leaf damage, and larvae.

Cultural Methods: a) Deep summer plough might expose the pupae to sunlight or predators

                            b) Keep the field and surrounding area free from weeds

                            c) Plant early in the growing season

                            d) Avoid planting new crops near infested field

                            e) Look for egg mass and crush them by hand

                            f) Provide proper nutrients to plant so that they can withstand infestation

Traps: Use pheromone traps to monitor and kill the adult insects.

Chemical Control: "In some areas resistance to insecticides may be widespread and control can be difficult. Recommended insecticides for Spodoptera spp. include esfenvalerate, carbaryl, chlorpyrifos, malathion, permethrin, and lamba-cyhalothrin." (CABI 2017)

Genetic Modification: One possibility is to modify maize to produce a toxin such as Bt toxin, which has proved succesful in some crops like cotton and maize in the US. Fred Gould of NC State made a video (below) of possible problems will considering genetic modficiation as the solution to the FAW problem in Africa 

 

References

CABI Crop Protection Compendium. (2017). Spodoptera frugiperda (fall armyworm) datasheet. Available at: https://www.cabi.org/isc/datasheet/29810. [Accessed 4 December 17]. Paid subscription required.

Zebdewos Salato, Jayne Crozier, Negussie Efa, Margaret Mulaa (2017). Fall armyworm (FAW) on maize. Pest Management Decision Guide: Green and Yellow List. https://www.plantwise.org/FullTextPDF/2017/20177800723.pdf

FAO Briefing Note on FAW (2017). http://www.fao.org/food-chain-crisis/how-we-work/plant-protection/fall-armyworm/en/