Fall armyworm in a maize whorl. (Photo by FAO)

Farmer education and community action are critical elements in the strategy to sustainably manage fall armyworm (FAW) populations. This is especially true for smallholder farmers in Africa. The United Nations’ Food and Agriculture Organization (FAO) has taken the lead in the provision of education to manage FAW.

The FAO is making use of Farmer Field Schools (FFS) to implement an integrated ecological and sustainable FAW management strategy for smallholders in Africa. FFS is an intensive farmer education approach promoted by FAO and many organisations worldwide, establishing platforms for farmers to learn, experiment and exchange information.

It is in this context that the FAO recently published an educational guide to provide smallholder farmers in Africa with the necessary information to implement an integrated pest management system.

Armyworm identification

The first step in FAW management is the identification of the worm. The pest is new to Africa and farmers need to be able to distinguish it from other pests. It is important to identify it in its various life cycle stages – from egg to larvae and pupae to adult.

Half-grown or fully-grown caterpillars are the easiest to identify. The larvae are generally characterised by three yellow stripes on the back, followed by a black, then a yellow stripe on the side. Look out for four dark spots forming a square on the second to last segment. Each spot has a short bristle (hair). The head is dark and shows a typical upside-down Y-shaped pale marking on the front.

The larvae are generally characterised by three yellow stripes on the back, followed by a black, then a yellow stripe on the side. (Photo by FAO)

Many other maize pests resembling the FAW are present in Africa. They are most easily differentiated when one can identify the worms in their various life stages and the type of damage they cause. The maize stalk borer closely resembles the FAW, for example. The most important stem borer pests on maize are Busseola fusca, Chilo partellus and Sesamia calamistis. The difference in behaviour among stem borers and FAW can help farmers to distinguish between them.

The extensive damage caused by FAW in maize can be seen in this photo. (Photo by FAO)

The type of damage inflicted will look different with each type of infestation. The main differences between stem borer and FAW infestations are:

  • The FAW causes big holes in maize leaves. Generally, the ‘big holes’ associated with the FAW are not present in stem borer attacks (for both young and old larvae).
  • Stem borer damage is characterised by a typical dead heart (a deformed, stunted plant), which is easily seen in young maize plants.
  • As stem borer larvae mature, they are found less frequently in the whorl (the leaves around the node of a stem), contrary to the FAW. They can, however, be found in the maize stem, where they leave holes with visible frass (excrement of insect larvae).

FAW app helps smallholder farmers

The Food and Agricultural Organization recently launched the Fall Armyworm Monitoring and Early Warning System (FAMEWS) mobile app, which enables farmers to identify, report and map the spread of the worm.

The app is useful on two fronts: for farmers and agricultural workers in the direct management of their crops to prevent further infestations and to reduce damage; and for all role-players involved in managing fall armyworm in Africa, by providing vital analysis on risks, spread and management.

Management options

The most promising options available to African smallholders to manage FAW are presented here. These options build on experiences from the Americas and the latest available research in Africa, reflecting integrated pest management (IPM) strategies. There are several management options for FAW that work well in combination.

Crop management: Good crop management techniques can help prevent FAW infestation. Follow the right planting dates and avoid late plantings, i.e. staggered plantings (the planting of fields at different dates in the same area), as this will continue to provide the FAW with food. It is one of the most important recommendations for smallholders.

Good soil health and adequate moisture are critical – they are essential to grow healthy plants, which can better withstand pest infestation and damage. Unbalanced inorganic fertilisation of maize (especially excessive nitrogen use) can increase oviposition by female FAW.

Maize varieties: Certain maize cultivars are more resistant to the FAW, such as Bt maize, which is grown to control the maize stem borer. Bt maize has been genetically engineered by incorporating genes from the bacterium Bacillus thuringiensis (Bt) that produce insecticidal proteins that can kill crop pests. It is important, though, to note that insect populations are able to adapt to Bt proteins through the evolution of resistance.

Plant diversity: Plant diversity on farms reduces FAW infestation and supports natural enemies of this pest. Although female FAW moths prefer laying their eggs on maize plants, they also lay eggs on other plants, which could help smallholder farmers to divert the pest even if it is present in the area. A farm with monocultures of maize makes it easier for the pest to procreate.

Intercropping maize with plants that the FAW dislikes, or planting it nearby, will most likely force moths to move on to other areas more conducive to laying eggs. For example, smallholder farmers in Central America have found that planting maize in their traditional milpa systems – combining it with beans and squash – lessens pest attacks.

Biological control: The fall armyworm has many naturally-occurring enemies that feed on it. These enemies have the potential to substantially reduce FAW populations, but it is a major challenge to create the right conditions to realise the full potential of these beneficial organisms. Broad spectrum pesticides kill many of the beneficial insects.

Biological control agents (BCAs) include predatory insects that eat their prey, parasitoids (insects that are parasitic on other insects) and entomopathogens (microbial pathogens), such as nematodes, fungi, bacteria, viruses and protozoa, that are lethal to FAW.

  • Predators of the FAW kill several individuals either as eggs, larvae, pupae or adults. The following insects are predators to the FAW in various life stages: earwigs, ladybird beetles, ground beetles, assassin and flower bugs, and predatory wasps. Spiders, birds and bats have also shown to be predators of the FAW.
  • Parasitoids are organisms whose adults lay eggs either inside or attached to a single host organism. To enable development, the resultant larvae feed on the tissues of the host until they are fully grown and pupate. Parasitoid larvae always kill their host as the outcome of their development. The majority of parasitoids known to be associated with the FAW are wasps, and less frequently flies.
  • Entomopathogens are pathogens such as fungi, bacteria, viruses and nematodes that affect insects and can control FAW. Viruses such as the nuclear polyhedrosis virus (NPVs) and Spodoptera frugiperda multicapsid nucleopolyhedrovirus (SfMNPV) are lethal to the FAW. So are the fungi Metarhizium anisopliae, Metarhizium rileyi and Beauveria bassiana. In the case of bacteria, Bacillus thuringiensis (Bt), found in Bt maize, also kills the FAW.

Synthetic pesticides: Several synthetic pesticides have been used in response to the invasion of fall armyworm, including methomyl, acephate, cyfluthrin, benfuracarb, methyl parathion, carbaryl, endosulfan, carbosulfan, lindane, chlorpyrifos, cyfluthrin, diazinon, methomyl, and methyl parathion. Farmers must only use approved insecticides and apply the application dosage rates recommended on the product label.

An important aspect the FAO report fails to mention is that the application must only be made against young instar (phase between two periods of development) larvae less than 10mm long. This is according to a recent report by the Department of Agriculture, Forestry and Fisheries (DAFF) on FAW control in South Africa. According to the DAFF report, application against older larvae is not successful since they feed deep inside whorls of plants and are therefore protected from contact with the insecticide.

FAW checklist

The FAO guide for FAW control provides the following checklist of facts that all smallholder farmers should know:

  • Farmers need to be able to identify and differentiate the FAW (Spodoptera frugiperda) from the African armyworm (Spodoptera exempta), cotton bollworm (Helicoverpa armigera), stem borers and other worms.
  • They must recognise the different stages of the FAW and understand its life cycle.
  • Farmers need to know where to find the FAW in its different life stages on the plant, how the worm feeds on the plant, and what the damage looks like.
  • They must know which plants can serve as an alternative host.
  • They must also know which plants repel or attract the FAW. The same can be true for natural enemies. Plant diversity is important as food sources for natural enemies.
  • Farmers need to know which natural enemies of the FAW are present, how they attack the different stages of the worm and how many pests they can eat, parasitise or infect.
  • They must understand how plants can compensate for leaf damage in different stages of crop development. – Ursula Human, Farmbiz

To read the full report on The Integrated Management of the Fall Armyworm on Maize visit www.fao.org. For more information or to report a fall armyworm sighting contact Jan Hendrik Venter (DAFF) on 012 319 6384 or janhendrikv@daff.gov.za.