Why is it a problem?
The fall armyworm (FAW) is a polyphagous pest that damages more than 350 plant species belonging to 76 plant families (Montezano et al., 2018). The higher damage is found in maize and sorghum, which are their primary hosts (Casmuz & Juárez, 2010). The average fecundity of one FAW female is 1000 eggs (Mura et al., 2006) and can fly over 100 km per night (Song et al., 2020). Furthermore, FAW do not enter menopause, so they can migrate to new places with suitable environmental conditions (Du Plessis et al., 2020). The high fecundity, high migratory ability, and wide host range of the FAW pose high threats to the maize crop.
Where and when is it a problem?
In Bhutan, FAW was first observed damaging maize in Dabchagang and Pepchu in Guma Gewog and Mendugang in Dzomi Gewog, Punakha, in September 2019 (Mahat et al., 2021). Currently, FAW has been detected damaging maize in eight Dzongkhags (Chukha, Punakha, Paro, Thimphu, Mongar, Dagana, Wangdiphodrang, and Sarpang). Maize is damaged by FAW from the seedling to the ear development stage. FAW defoliate, damage whorls, and feed on ears, resulting in yield losses (Capinera, 1969).
IDENTIFICATION, BIOLOGY & SYMPTOMS
Refer the following guides
- A guide for FAW Identification and Management
2. Fall Armyworm photo guide: identification https://www.fao.org/3/ca4856en/ca4856en.pdf
Confusion with other pests:
FAW are often confused with beet armyworms, Spodoptera exigua (Hübner), and yellow-striped armyworms, Spodoptera ornithogalli (Guenée).
Track the presence of FAW moths by using pheromone traps. Contact NPPC for traps.
Surveillance and Scouting
Examine maize fields for damage (scars) on the leaves, which can indicate the presence of FAW larvae. Once the presence is confirmed, conduct simplified scouting as explained in “How to Identify and Scout for the Fall Armyworm” (https://sawbo-animations.org/708) by Scientific Animations Without Borders. Begin scouting from the seedling to the ear development stage. Control measures should target small larvae (L1-L3) feeding superficially on leaves. Refer to Fall armyworm in Asia: a guide for integrated pest management by CIMMYT (https://repository.cimmyt.org/handle/10883/21658) for detailed information on scouting during the vegetative and reproductive stages.
Effect of variety
The commonly grown maize varieties in Bhutan, Yangtsi, Bhur Ashom, Shafangma, and Wengkhar hybrid, are damaged by FAW.
Non- chemical management
- Handpicking of egg masses and larvae is widely used farmers in Africa (Yigezu & Wakgari, 2020).
- Application of sand into the whorls of maize plants cause larval desiccation (Hruska, 2019).
- Burning crop residues to destroy eggs, larvae, pupae, and adults(Assefa, 2018).
- Field ploughing to expose pupae to natural enemies (Abrahams et al., 2017).
Insecticides should be applied based on the Economic Threshold Level (ETL), which indicates the pest population, cost of pest control, and value of the crop (Prasanna et al., 2019). Refer to Fall armyworm in Asia: a guide for integrated pest management by CIMMYT (https://repository.cimmyt.org/handle/10883/21658) for detailed information on the economic threshold level for vegetative and reproductive stages.
These insecticides are recommended based on trial results in Africa and Asia.
- Foliar spray with low-toxicity Insecticides: Chlorantraniliprole 18.5 SC and Emamectin benzoate 5 SG against small larvae (L1-L3) feeding on maize leaves.
- Targeted spray at infested whorls with Chlorantraniliprole and Emamectin benzoate is recommended. However, it is difficult to control the larvae after they move into whorls and ears.
On- going research activities at Entomology unit, NPPC
- Host- Plant Resistance
- Evaluation of three Elite (African) and four traditional (Bhutanese) maize varieties against FAW (second year)
- Effect of trichome density on African and Bhutanese maize varieties against FAW damage (first year)
- Insecticide efficacy trial
- Evaluation of low toxicity insecticides (Chlorantraniliprole and Emamectin benzoate) against FAW (second year)
Check out the following link:
- First record of FAW in Bhutan https://www.sciencedirect.com/science/article/abs/pii/S1226861520307573#:~:text=We%20report%20the%20first%20detection,a%20serious%20pest%20of%20many.
- ASEAN FAW Action Plan : https://www.aseanfawaction.org/
Version: NPPC 2022. Fall armyworm V2.0. Bhutan Pest Factsheet. www.PestsofBhutan.nppc.gov.bt. Date produced: December 8, 2022. Contact: firstname.lastname@example.org