Fall Armyworm (FAW), Spodoptera frugiperda is one of the majorly invasive pests that are found in maize and cause severe damage to the crop at all stages of its growth. The pest is native to Tropical and Subtropical regions of America. It is a polyphagous pest with a number of hosts exceeding 80 species. It was reported in India, in July 2018. Due to the open border between India and Nepal and the rapid migrating tendency of the pest, its arrival was soon reported in Nepal as well in August 2019. It brought about a great deal of damage to the places of its arrival. Even though the level of incidence and damage varies from place to place, farmers have reported up to 80% crop loss in extreme cases. According to CIMMYT, in Nepal, the fall armyworm has the potential to cause maize yield losses of 20-25%, which translates to the loss of more than half a million tons of the annual maize production — estimated at around $200 million. If the pest is left unrestrained, its impact will be huge for farmers and the economy. In addition to that, Nepal’s climatic conditions are believed to be suitable for its population establishment which could possibly lead to 100% crop loss in maize if not managed properly.
The female moths lay egg masses on the upper or underside of the leaf and are covered with tan-colored scales. Each egg mass contains 50-150 eggs. The incubation period varies from 4-5 days. The larvae are smooth-skinned and vary in color from light tan or green to dull grey body with three creamy yellow dorsal and lateral lines. The larva contains a reddish brown head with a predominantly white, inverted Y-shaped suture between the eyes. The larva contains 6 instars in which the larval period varies from 15-18 days. On the 8th and 9th abdominal segments, four large spots are arranged in a square shape on segment 8 and in a trapezoid pattern on segment 9. The pupa is reddish-brown in color. After 7-9 days, adults emerge from pupae. The forewing of adult male moths consists of a fawn-colored spot and a white patch at the apical margin of the wing while female moths are less distinctly marked ranging from uniform grayish brown to a fine mottling of grey and brown. The total lifecycle completes in about 30-35 days which vary according to climatic conditions. Adult longevity varies from 4-7 days. The adult moth can fly up to 500 km before oviposition. Being a lepidopteran pest, HOW’s life cycle completes in four phases: Egg, Larva, Pupa, and Adult.
NATURE OF DAMAGE:
FAW is a voracious feeder and attacks all stages of maize crop from seedling emergence to ear development. The young larvae of FAW feed in and around the whorl leave by scraping and skeletonizing the upper epidermis leaving a silvery transparent membrane resulting in papery spots. The damage also results in pinhole symptoms on the leaves. Older larvae remain and feed inside the whorl. The damages by late instars (4th instar onwards) result in extensive defoliation of leaves and the presence of large amounts of faecal pellets in whorls. Damage during vegetative stage leads to leaf damage but if damage happens during the reproductive stage it may damage tassels or may bore inside the corn ear and eat away the kernels. The whorl damage by FAW results in significant yield losses while ear feeding results in both quality and yield reduction.
Integrated Pest Management:
Integrated Pest Management (IPM) is the most effective and preferred method of FAW management (Day et al., 2017). IPM strategies have been formulated and have been upgraded from time to time. In Nepal, the pest is in the phase of incidence, thus the IPM method of pest control will be the best method for management. IPM method of pest management includes various practices of pest control like cultural, physical, and biological methods.
IPM schedule, Infestation threshold for crop growth, and spray schedule against FAW are given below:
- Deep plough the fields to expose pupae to sunlight and predatory birds (not recommended under conservation agriculture)
- Add neem cake @ 200kg/acre to the fields when maize is grown with zero tillage or wherever possible
- Maintain field bunds clean and plant flowering plants such as marigold, sesame, Niger, sunflower, coriander, fennel, etc. to attract natural enemies.
Sowing to six-leaf stage
- Timely and uniform sowing over a larger area
- Follow ridge and furrow planting method instead of flatbed sewing
- Apply only the recommended dosage of NPK as basal dose
- Seed treatment: Cyantraniliprole 19.8% + Thiamethoxam 19.8% FS @ 6 ml/kg of seed offers protection for 15-20 days of crop growth
- Plant 3-4 rows of Napier grass/hybrid Napier as trap crop around maize fields
- Intercrop maize with legumes, , pigeon pea, cowpea, black gram, kidney bean etc. in 2:1 to 4:1 ratio
- Erect bird perches @10/acre to encourage natural FAW predation by birds
- Install pheromone traps @ 4/acre soon after sowing and monitor moth catches
- Adopt clean cultivation to eliminate possible alternate hosts
- Destruction of egg masses and larvae by crushing
- Application of sand or soil mixed with lime in 9:1 ratio into the whorl of maize plants
- First spray should be with 5% neem seed kernel extract (NSKE) or azadirachtin, 1500 ppm (1 litre/acre) @ 5ml /litre after observation of one moth/trap/day or 5% FAW infestation on trap crop or main crop
- If monitoring indicates more than one month/trap/day install pheromone traps @ 15/acre for mass trapping [Note: For the success of mass trapping go for community action] OR release egg parasitoids , Telenomus Remus@ 4000/ acre or Trichogramma pretiosum @16,000/acre. Two releases of parasitoids at weekly intervals should be done. [Note: Release of parasitoids should not be done if mass trapping is followed]
- At 5-10% infestation whorl application of Bacillus thuringiensisKurstaki formulations (400g/acre) @ 2g/litre or Metarhizium anisopliae or Beauveria bassiana with spore count of 1×108cfu/g (1 kg/acre) @ 5g/litre or SfNPV (600 ml/acre)@3ml/litre or entomopathogenic nematode (EPN) (4kg/acre) @20g/litre of water is recommended
- If infestation is more than 10%, whorl application of any one of the recommended insecticides for FAW, ,Chlorantraniliprole 18.5 SC (80 ml/acre) @ 0.4 ml/litre; Thiamethoxam 12.6 % + Lambda cyhalothrin 9.5% ZC (50ml/acre) @ 0.25 ml/litre; Spinetoram 11.7 % SC (100ml/acre) @ 0.5 ml/litre; Emamectin benzoate5% SG (80g/acre) @ 0.4g/litre is recommended
Seven leaf stage to flowering
- Monitoring of FAW using pheromone traps @ 4/acres should be continued
- Spray 5% NSKE or azadirachtin, 1500 ppm (one litre/acre) @5 ml /l after observation of one moth/trap/day or 5% of fresh FAW infestation
- If infestation is more than 10%, whorl application ofBacillus thuringiensis Kurstaki formulations (400g/acre) @ 2g/litre or Metarhizium anisopliae or Beauveria bassiana with spore count of 1×108cfu/g (1 kg/acre) @ 5g/litre or SfNPV (600ml/acre)@3ml/ litre or entomopathogenic nematode (EPN) (4kg/acre) @20g/litre of water is recommended
- If infestation is more than 20%, whorl application of any one of the recommended insecticides for FAW,,Chlorantraniliprole 18.5 SC (80 ml/acre) @ 0.4 ml/litre; Thiamethoxam 12.6 % + Lambda cyhalothrin 9.5% ZC (50ml/acre) @ 0.25 ml/litre; Spinetoram 11.7 % SC (100ml/acre) @ 0.5 ml/litre; Emamectin benzoate5% SG (80g/acre) @ 0.4g/litre is recommended.
Poison baiting is effective for late instar larvae and is optional. Mix 10 kg rice bran + 2 kg jaggery with 3 litres of water. Keep the mixture for 24 hours to ferment. Add any one of the recommended insecticides mentioned above at their recommended dosages and 1 kg of sand just half an hour before application. Make into small pellets and apply into whorls of infested plants only. [Use hand gloves during mixing and application]
Flowering to harvest
- Hand picking and destruction of larvae boring into ears
- At 10% ear damage, application of Bacillus thuringiensiskurstaki formulations (400g/acre) @ 2g/litre or Metarhizium anisopliae or Beauveria bassiana with spore count of 1×108cfu/g (1 kg/acre) @ 5g/litre or SfNPV (600ml/acre)@3ml/ litre of entomopathogenic nematode (EPN) (4kg/acre) @20g/litre of water is recommended.
Pheromone traps– Funnel trap with FAW lure should be installed at a height-adjusted each week matching with crop canopy. Traps should be separated by a minimum distance of 75 feet. Observe traps for the number of moths caught twice or once in a week and work out the catch/day. FAW lures should be changed once in 30 days in case of monitoring.
Preparation of Neem Seed Kernel Extract (NSKE) for one acre:
10 kg of neem seed kernel is required for one acre. Grind 10 kg of neem seed kernels to make powder. Soak the powder in 50 liters of water overnight. Stir and filter the contents using a cotton cloth. Add 200 g detergent powder or 200 ml of soap solution to the filtered solution. Make up the volume to 200 liters by adding water.
Caution upon release of egg parasitoids:
Minimum one week interval should be there between parasitoid release and application of neem or chemical insecticides
Precautions for pesticide use:
Not more than two chemical sprays are to be used in the entire crop duration. Same chemical should not be chosen for the second spray. Sprays should always be directed towards whorl and applied either in the early hours of the day or in the evening time. Use protective clothing, facemask, and gloves during the preparation and application of pesticides. Enter the field only 48 hours after spraying the pesticide. The interval between the application of chemical insecticide and the harvest of corn should be a minimum of 30 days.
NATURAL ENEMIES OF FAW:
Source: (CABI, 2019)
Fall armyworm is a damaging pest for maize. In countries like Nepal where most people are unaware of modern agriculture practices, it can cause damage to an even greater degree. So, before it’s too late, our farmers should be made aware of this damaging pest and different management practices such as biological, cultural, and chemical. Biological practices, cultural practices, and integrated pest management (IPM) should be encouraged.