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Latest FAW Report

Updated Mar 25, 2026

Fall armyworm update – late March

Fall armyworm (FAW), Spodoptera frugiperda, remains present across much of the country. Pressure is now shifting. Many early crops have been harvested, especially in the North Island. Activity is increasingly concentrated in later-planted maize and sweetcorn. These crops have carried the highest infestations this season.

Moth flights continue to be detected, though numbers are more variable between regions. Egg laying is still occurring where green host material is available. Generations remain overlapping. Larvae of mixed sizes are still being found, but populations are becoming more localised.

Crop stage and risk

Most early-planted maize has now passed the risk. Attention should shift to late and replanted crops. These remain vulnerable, especially where plants are still green and actively growing.

It is the seedling and vegetative stages that suffer the greatest yield loss. This has been clear across the season. Late planting increases exposure to peak FAW pressure.

In grain crops, cobs continue to host high numbers of caterpillars. This includes FAW, but also other species. Damage is often hidden until harvest. There is only a short window for control before larvae enter the cob. Once inside, control is poor.

Do not assume late crops are safe. Green leaf area and fresh silks will still attract egg laying.

Seasonal observations

Late-planted crops have consistently carried the highest FAW pressure this season. This is a key pattern.

In some paddocks, early instar FAW populations have declined rapidly. This is unlikely to be random. Sudden drops often indicate predation. Natural enemies are playing a strong role in population control.

Beneficial insects have again been widely observed. Parasitism and predation have reduced many infestations before they reached damaging levels.

Beneficial insects

Parasitic wasps and predators remain important:

  • Cotesia ruficrus has been present, but numbers appear lower in some regions such as Westland compared with last season.
  • Meteorus spp. is abundant, with many cocoons observed in infested areas.
  • Generalist predators, including spiders, could be responsible for rapid reductions in some FAW populations.

Broad insecticide use can disrupt these beneficial species. This may allow pest populations to rebound. Consider this risk before spraying.

Other pests present

Two other caterpillar pests remain active and are often found alongside FAW:

  • Helicoverpa armigera is common in cobs. Damage is often hidden and may only be seen at harvest.
  • Mythimna separata continues to feed on leaves and can cause rapid defoliation.

Correct identification remains important for management decisions.

Post-harvest management

This is now a critical step.

FAW pupae may remain in the soil after harvest. These can emerge and infest nearby crops.

“Pupa busting” reduces this risk:

  • Grazing residues helps remove food sources and disturb soil
  • Trampling by livestock can damage pupae
  • Shallow cultivation (to around 10 cm) breaks pupal cells and exposes them to birds and drying

This is one of the few effective non-chemical controls between seasons. It is often missed but can reduce local populations.

Volunteer maize plants after harvest are also a risk. These are preferred host plants and can carry FAW into cooler months. Remove or graze these early.

Planning for next season

Weather often drives planting delays. But delayed planting has increased FAW risk this season.

Where possible:

  • Prepare early to take advantage of planting windows
  • Aim to avoid peak FAW pressure during early crop growth
  • Consider how planting timing fits within local pest pressure patterns

This is one of the most effective long-term strategies available.

Scouting remains essential

Trap data shows moth activity. It does not indicate crop damage.

Direct crop inspection is still required:

  • Walk paddocks regularly
  • Check both leaves and cobs
  • Monitor silks for early infestations
  • Focus on late and green crops

Timing is critical. There is only a short window to control larvae before they become protected.

Key actions for this week

  • Continue scouting late maize and sweetcorn
  • Check cobs and silks carefully
  • Avoid spraying large or protected larvae
  • Carry out post-harvest residue management and cultivation
  • Remove volunteer maize plants early
  • Consider planting timing for next season

Local information improves timing and outcomes. Your observations are important. Please report FAW activity and outcomes to ashley.mills@FAR.org.nz.

Regional Updates

Northland

Updated Mar 25, 2026
  • Most maize crops will have passed the high-risk stage as they are mature or have been harvested. Later-planted crops can become "green Islands" for adult FAW seeking to lay eggs.  These crops should still be scouted regularly as large moth flights are being observed, especially in the Far North.

Auckland and Waikato

Updated Mar 25, 2026
  • FAW is widespread in small populations, and small moth flights have been recorded.  Most maize crops are past the risk period, although late-planted crops and sweetcorn are still threatened by the autumn FAW populations.

Bay of Plenty

Updated Mar 25, 2026
  • FAW is widespread in small populations, recent moth flights have been recorded.  Most maize crops are past the risk period, although late-planted crops and sweetcorn are still threatened by the autumn FAW populations.

Gisborne

Updated Mar 25, 2026
  • An increase in FAW moth numbers has been observed along with reports of low-level infestations. Walk your sweetcorn crops and later planted maize crops and consult your advisor if you have concerns.

Westland

Updated Mar 25, 2026
  • Populations are widespread across Westland. A large moth flight has been recorded this week in the Hokitika region; however, with the harvest of most maize crops only a few weeks away, it is unlikely that the resulting larvae will cause much concern. A large percentage of cobs already have Corn earworm (Helicoverpa armigera) or FAW present.  A small number of Cosmopolitan armyworm (Mythimna separata) have also been observed.

Tasman

Updated Mar 25, 2026
  • Populations of FAW have been observed in multiple maize paddocks.  Maize is now well advanced and should have outcompeted any FAW pressure, although grain crops and sweetcorn crops should still be scouted regularly.  Parasitism by Cotesia ruficrus has been observed in sweetcorn and maize crops. Walk your crops and identify damage and larvae. Consult with your advisor if you have any concerns.

Taranaki and Manawatu-Whanganui

Updated Mar 25, 2026
  • Male FAW moths have been caught in pheromone traps in the region.  Reports have confirmed FAW larvae in crops; however, damage appears to be localised in paddocks. Scouting crops should be factored in as often as possible to identify any larvae in paddocks that may still be at risk.

Canterbury

Updated Feb 25, 2026
  • There have been FAW observations in a small number of Canterbury maize crops.  These are likely moths that have been blown in recently from neighbouring regions that saw moth flights in late January or early February.  Maize crops are well advanced, and the small FAW populations reported should not pose a threat to crops.  Scouting is still important to track the pest, especially in any sweetcorn or later planted maize crops.

Hawke's Bay

Updated Feb 25, 2026
  • FAW reports have been received this month however, only small populations have been observed and do not appear to be a threat to advanced maize.  We urge sweetcorn growers to continue to stay vigilant.

Is it Fall armyworm?

There are three key characteristics used in combination that will help identify FAW.

  • First, a distinct ‘Y’ on the head leading into the dorsal line.
  • Second, four trapezoid patterned dots on the body segments.
  • Finally, four pronounced dots in a square pattern at the rear.   

Other pests may share a similar identification but not all three key markings together.

 

How to identify FAW

Photo courtesy Bioeconomy Science Institute (PFR) 

Fall armyworm lifecycle and damage

Should I be monitoring my crop?

Crop monitoring is vital for managing pests in maize and sweetcorn effectively. Regular monitoring starts as soon as crops are planted.  The most effective crop monitoring tool is crop scouting, which is defined as 'careful continuous observation', where a crop scout walks the whole crop to assess infestations and fresh damage. Crop scouting helps detect pest presence early, preventing significant damage during the vulnerable establishment stage of crops. It enables growers to assess pest populations, identify affected areas, and determine the most effective and timely control measures. Monitoring also supports integrated pest management (IPM) by providing insights into the activity of natural enemies, like Cotesia ruficrus. This ensures that interventions, such as selective insecticides, are used only when necessary, reducing costs and minimising environmental impact.  It is also a great opportunity to assess crop status, nutrient requirements, other pests present, and disease and virus pressure, like Northern leaf blight.

How do I monitor my crop?

1. Identify the crop stage and plan the scouting choose a pattern (zig-zag or "W" shape) to cover all parts of the field.

2. Walk the field properly follow the planned path, and stop at regular points across the field.

3. Inspect the plants check several plants at each site for FAW signs:

  • Damage on leaves
  • Frass (insect droppings)
  • Larvae feeding in the whorl or on leaves
  • Identify and record the presence of other pest species.
  • Observe and record any beneficial species, especially Cotesia ruficrus.

4. Count and record

  • Record the total number of plants checked.
  • Record the number of plants with FAW damage or larvae.
  • Record the size of FAW larvae.
  • Record sightings of other pests or beneficial insects.

5. Calculate the percentage use the formula:

  • (Number of damaged plants ÷ Total plants checked) × 100
  • Example: (24÷150) ×100=16%

6. Compare to the threshold use the threshold table to decide if action is needed

7. Repeat scout crops as often as possible, ideally once a week at a minimum, following a different path each time.

Note: Checking more sites within a crop gives a far better picture of Fall Armyworm infestation than checking more plants per site. The key is spatial coverage—aim for around 50 sites (more for large paddocks, fewer for small ones)— or enough until you are confident you understand the infestation’s spread and severity

 

When plants are small and it is easy to move through the crop, we recommend a "W" shape scouting pattern.

 

 

When plants reach the later whorl stage, it can become harder to move through the crop.  We recommend a zig-zag-shaped scouting pattern, allowing quicker and more effective coverage of the field.

Monitoring for adult FAW moths

Why does the size of the caterpillar matter?

Identifying the size of Fall armyworm (FAW) larvae is important for effective targeted chemical intervention because smaller larvae are more vulnerable to insecticides. Early detection of young larvae, typically less than 10 mm in length, allows for more effective control before they burrow into the whorl or cob. As larvae grow larger, they become harder to kill, cause more damage, and may require higher chemical inputs, which increases cost and environmental impact. Accurate assessment of larval size ensures the timely and efficient application of control measures.

 

Source: Corteva Agriscience

Economic Thresholds

Economic thresholds are very important in an Integrated Pest Management (IPM) strategy because they help make smart decisions about pest control. An economic threshold is the level of pest numbers or damage at which action must be taken to prevent the pest from causing too much damage and reducing the crop yield in a way that would cost more money than the cost of controlling the pest.

This is the current New Zealand economic thresholds guide developed by Bioeconomy Science Institute (AgR)

What are other similar pests in maize?

What are beneficials?

Let the good guys do the work!

A wide range of beneficial predators and parasitoids contributes to the natural control of Fall Armyworm (FAW) in arable cropping systems, including maize and sweetcorn. These natural enemies can be categorised into resident and transient species. Resident species live within the crop environment year-round, playing a crucial role in controlling pests during crop establishment when the plants are most vulnerable. Transient species, on the other hand, move into the crop only when a pest population is present and serve as an important part of pest suppression.

Predators

Predators, such as spiders, are among the most effective natural enemies of FAW. Spiders can be abundant in maize and sweetcorn systems, preying on a variety of FAW life stages, including eggs and larvae. These predators are relatively easy to spot due to their larger size and active hunting behaviour. Their impact is immediate as they capture and consume their prey directly and may contribute to a significant reduction in FAW populations.

Parasitoids

Parasitoids, such as the wasp Cotesia ruficrus, are less visible but very important in controlling FAW. Cotesia ruficrus lays its eggs inside FAW larvae, and the developing wasp larvae consume the host from within, eventually killing it. This activity often goes unnoticed until the later larvae or pupal stage when the parasitoid creates a bunch of cocoons within or near the remains of the host. These parasitoids can also be monitored by examining host larvae for signs of parasitism or identifying cocoons in the crop.

Integration with Integrated Pest Management (IPM)

IPM strategies aim to maximise the populations of resident beneficial species, such as spiders, while encouraging the activity of transient species like Cotesia ruficrus. With the reduction or withdrawal of broad-spectrum insecticides, it may take time for resident populations to recover and establish, but transient species can readily colonise a crop when FAW is present. Encouraging biodiversity, maintaining habitats, and using selective insecticides can help optimise the roles of these natural enemies in FAW management.

Plant & Food Research has identified Cotesia ruficrus and spiders as key natural enemies of FAW in New Zealand maize and sweetcorn crops. However, many other predators and parasitoids also contribute to the natural suppression of FAW populations, forming a diverse and dynamic system of biological control. This natural management method is a critical component of sustainable FAW control and reduces reliance on chemical insecticides.

Natural predators of FAW

Fall armyworm resistance management

Insecticide options

Products Last Reviewed Jan 30, 2026
120 g/L Jemvelva® active (Spinetoram)
Sparta™

Mode of Action: Jemvelva® active is active on all larval life stages and enters the insect primarily through the digestive system (ingestion activity) and secondarily through the insect exoskeleton (contact activity).

IRAC Group: 5

Beneficial Impact: Anecdotal evidence suggests this active ingredient is suspected to be harmful to small parasitic wasps

Spray Information
Bacillus thuringiensis var. kurstaki
DiPel DF

Mode of Action: Microbial disruptors of insect midgut membranes

IRAC Group: 11

Beneficial Impact: Low Lepidopteran-specific microbial toxin that must be ingested.

Spray Information
Chlorpyriphos
Multiple generics

Mode of Action: Organophosphate. Has contact and vapour action and also acts as a stomach poison when ingested. Acts directly on the nervous system of susceptible pests.

IRAC Group: 1B

Beneficial Impact: High impact on all insects, very harmful to beneficials.

Spray Information
lambda-cyhalothrin
KARATE ZEON, CYHELLA, HALEX CS, LAVRON, TAEKWANDO 250 CS

Mode of Action: Synthetic pyrethroid. Primarily a contact and stomach poison with direct effects on the nervous system of susceptible insect pests.

IRAC Group: 3A

Beneficial Impact: Highly toxic to ALL beneficial insects

Spray Information
Tetraniliprole 480 g/L
Vayego Forte

Mode of Action: Group 28 compounds modulate insect ryanodine receptors (RyRs), which are calcium channels critical for muscle function. By binding to these receptors, they cause muscle paralysis and cessation of feeding, leading to insect death.

IRAC Group: 28

Beneficial Impact: Low impact on most beneficials, although effects on Cotesia ruficrus are currently unknown.

Spray Information
Chlorantraniliprole 200 g/L
Coragen®

Mode of Action: Group 28 compounds modulate insect ryanodine receptors (RyRs), which are calcium channels critical for muscle function. By binding to these receptors, they cause muscle paralysis and cessation of feeding, leading to insect death.

IRAC Group: 28

Beneficial Impact: Harmful to some beneficial insects – particularly some foliage-dwelling predators which may be used in Integrated Pest Management.

Spray Information