Fall Armyworm Management in Maize and Sweetcorn

Plant & Food Research kindly hosted this year’s Fall Armyworm (FAW) Research Workshop at their Mt Albert site in Auckland. The day opened with a whakatau led by Hone Ropata of Plant & Food Research, setting a welcoming tone for a day of knowledge sharing and collaboration.

Researchers from across New Zealand—including Plant & Food Research, AgResearch, the Foundation for Arable Research (FAR), Scion, Manaaki Whenua – Landcare Research, Lincoln University, the University of Waikato, and independent entomologist Dr Jenny Dymock—shared updates on their current FAW-related work.

We were also fortunate to receive international contributions from Dr Melina Miles (Queensland Department of Primary Industries) and Dr Luciana Elizalde (National University of Comahue, Argentina), offering valuable global perspectives.

The 49 attendees engaged in in-depth discussions on a wide range of topics, including field observations, laboratory findings, predictive modelling, cropping strategies, and integrated pest management (IPM). The workshop also explored future research priorities for New Zealand, with a strong emphasis on collaboration and aligning scientific outputs with the needs of growers and industry stakeholders.

• Activity: Adult Fall Armyworm (FAW) moths are nocturnal and are most active during the evening and early night. They rest on plants or in shaded areas during the day.
• Feeding: Adults need to feed on nectar and are attracted to flowering plants, but they do not cause crop damage themselves.
• Dispersal: FAW moths are strong fliers, capable of travelling long distances (up to 100 km per night) during migration or when searching for suitable host plants.

• Site Selection: Female moths normally lay their eggs on the underside of leaves, particularly on young, actively growing plants, but they may also lay eggs on stems, weeds, or structures near crops if host plants are unavailable.
• Egg Mass Characteristics: Egg masses normally contain 100–200 eggs, with a single female capable of laying up to 1,000 eggs over her lifetime.  Eggs are typically covered with a fuzzy, whitish to light-brownish, silk-like layer, which are scales from the female.  This helps to protect them from predators and environmental conditions.
• What to Look For: Small, dome-shaped eggs arranged in clusters, often with the fuzzy covering visible. Focus inspections on young plants and the undersides of leaves near the crop canopy.

Damage Description

• The newly hatched larvae feed normally on the underside surface of leaves, creating tiny "windowpane" scars or translucent patches where the upper epidermis has been removed.
• Small larvae are gregarious and group together as protection from predators. Therefore, you see a shot-hole appearance to the leaves, where many small caterpillars are feeding together in a small group
• Damage is minimal at this stage and can be detected by observing this damage as multiple plants express the same damage in a very close proximity.  Larvae produce a silk thread and “balloon” to nearby plants as they progress through these early growth stages.

Appearance

• Larvae are very small (1-3 mm), pale green with a black head capsule.
• Feeding is typically concentrated near egg-laying sites, often the upper leaves.
• During the day, multiple larvae can be found in the center folds of a plant, showing window-like damage.

Damage Description

• As the larvae grow, they begin chewing small holes in the leaves, creating a "shot-hole" appearance. Feeding starts to become more noticeable, but the overall damage is still relatively limited.  At this stage larvae have normally spread to plants in a radius of a few meters from the original egg mass.

 Appearance

• Larvae grow to about 6-9 mm and begin to show dark stripes along their bodies.
• The three key identification characteristics are expressed but may be hard to see without a magnifying glass.
• Feeding is more spread out on the plant.

Damage Description

• The larvae feed more voraciously, creating larger holes and tears in the leaves. They begin to burrow into the whorl (young, folded leaves in the centre of the plant), leaving behind frass (sawdust-like excrement). The damage in the whorl can result in "tattered" leaves when they unfurl.

Appearance

• Larvae reach 15-25 mm and show distinct brown, green, or yellowish colouring with visible stripes.
• Larvae express all of the key identifiable characteristics and can be identified easily with the naked eye

Damage Description

• At this stage, FAW causes the most severe damage. The larvae feed deep in the whorl and can tunnel into the growing point, killing the plant if the growing point is damaged. In maize and sweetcorn, the larvae often burrow into the ear, silks, or cob, leading to direct yield loss and contamination. Large amounts of frass may be visible at the whorl or feeding sites.

Appearance

• Larvae are at their largest (25-40 mm), with a robust, striped body.
• They exhibit a distinct pattern on their body and head and can be identified easily with the naked eye

Pupation Process

After completing the larval stage, FAW larvae normally move to the soil to pupate, although some can be found still in the whorl or cobs. Mature larvae burrow around 5 cm into the soil, creating a small chamber in which they pupate. If the soil is compacted or unfavourable, larvae may pupate on the soil surface under leaf litter or debris.

• Duration: Pupation typically lasts 7–14 days under warm conditions, but it may take longer in cooler temperatures.
• What to look for in Soil: Pupation sites may be identified by disturbed soil or shallow holes. Scratching the surface away with a trowel can help identify a pupa, especially when plants have fresh signs but no residing larvae.
• Pupal Characteristics: Pupae are smooth, and change through greens to reddish-brown colouration, and range from 15–20 mm in length. They are similar to other noctuid pupae, and identification is difficult.  Found underneath plants expressing typical FAW damage but with no larvae present, can be a good indication that the pupa are FAW.

Helicoverpa armigera is a significant maize and sweetcorn pest in New Zealand, The female moth can lay several hundred eggs, laid singly and at their most damaging at the silking stage where larvae can enter cobs with the potential to cause significant economic damage. 

Helicoverpa armigera factsheet

Mythimna seperata is a maize and sweetcorn pest in New Zealand due to its voracious feeding, causing extensive leaf damage and reducing crop productivity.  This pest also feeds on grasses so nearby pastures can act as a population reservoir

Mythimna separata factsheet

Spodoptera litura is not a direct pest of maize and sweetcorn but can appear in paddocks feeding on weeds in the undergrowth.  When there are large numbers, it may feed on the leaves of maize and sweetcorn and is a major pest of leafy vegetable crops. Tropical armyworm is often confused with Fall Armyworm.

Spodoptera litura factsheet

The greasy cutworm, is a pest of maize, sweetcorn and many other agriculture crops in New Zealand, cutting seedlings at the base and causing significant crop loss, particularly during early growth stages in the spring.  Populations overwinter in crop residue and weeds.  winter and spring paddock management is key to minimising the damage from this pest.

Cotesia ruficrus is a parasitoid wasp present in New Zealand that targets caterpillars, including Spodoptera species. It was released in the 1970s as a biological control agent for the noctuid pest species, Agrotis ipsilon (greasy cutworm) and Mythimna separata (Cosmopolitan armyworm). Cotesia ruficrus has been very successful in reducing the pest status of M. separata in maize and sweetcorn crops. 

C. ruficrus parasitises larvae by laying eggs inside them, with emerging larvae consuming the host. Its potential impact on Spodoptera frugiperda (Fall Armyworm) in New Zealand remains uncertain however widespread parasitism of FAW has been observed. Understanding its role in maize and sweetcorn crops could inform integrated pest management (IPM) strategies. Further research is needed to determine its effectiveness against FAW in New Zealand’s environment.

• Check the product label to ensure registration for FAW in maize and sweetcorn,and follow instructions.
• Target susceptible FAW stages, especially early instar caterpillars, while still exposed on the leaves.
• Use selective insecticides to minimise impact on beneficial insects.
• Assess recovery time for beneficials if broad-spectrum insecticides were recently used for a different pest.
• Determine the health of natural enemy populations before applying insecticides.
• Consider seed dressings for initial FAW protection and their residual efficacy.
• Evaluate how long the chosen insecticide will remain effective.
• Ensure compliance with MRLs for domestic and export markets.
• Plan for increased FAW and other caterpillar pest risk after insecticide efficacy declines.
• Assess FAW populations and other caterpillar pests after spraying to observe efficacy.
• Calibrate spray equipment for uniform application and proper droplet size.
• Follow safety guidelines and provide protective equipment for workers.
• Explore additional options like biological controls and cultural practices as part of IPM.

By integrating these considerations into your pest management plan, you can optimise FAW control in maize and sweetcorn while minimising risks to beneficials, the environment, and worker health.