Published on 03/10/2023
‘Scaremongering’ is a negative term. It means to spread frightening or ominous reports or rumours, often exaggerated for the purpose of manipulation.
‘Forewarning’ is different. It is defined as informing someone of a possible future danger or problem. It might sound similar to scaremongering, but it has an entirely different quality. The information presented is mostly credible, and rather than being manipulative, it is presented to give people the best chance of preventing something bad.
When it comes to armyworms in New Zealand, which is it –scaremongering or forewarning? The distinction is important because the pest has now landed on our shores, and eradication is not an option.
What are armyworms? Fall armyworm (FAW) caterpillars have destructive feeding habits and tend to march together in mass migration. In large-scale movements, they devour crops, grass, and vegetation until the food supply in an area is exhausted. Once the food runs out, they move on en masse to find new crops.
New crops include almost anything. More than 350 plant species are vulnerable to this pest, although worldwide data shows the fall armyworm is primarily fond of barley and maize.
That is a problem. For many countries, these crops are significant sources of food and are pillars of their farming industries. New Zealand is one of them.
At the turn of the millennium, fall armyworm barely registered as a problem around the world. By 2016, Central and South American countries were overrun. In 2017, it crossed the South Atlantic Ocean and crops were being devoured in Sub-Saharan nations such as Kenya, Uganda, and Tanzania.
How was this migration possible? Wind currents. Adult fall armyworm moths are strong flyers and on the right air current can travel 500 kilometres at a time.
One year later, FAW had traversed the Indian Ocean, landing in India, Myanmar, Thailand and Cambodia. By 2019, much of China was affected.
This disturbing eastward migration continued throughout 2020-21, until in February 2022, fall armyworms were finally detected in New Zealand.
Should we worry? Even though it’s impossible to keep wind-borne fall armyworm out, countries that aggressively monitored for the presence of these pests have successfully preserved their crops through proactive vigilance.
In stark contrast, nations that were slow to engage in systematic monitoring and capture have been devastated by armyworms. Most notable among them were the Sub-Saharan Africa countries of Kenya, Uganda, and Tanzania. India has also suffered significant crop loss, as has China and large parts of the US.
The element that catches farmers off guard is the speed of the destruction, which is due mostly to the armyworm’s near-invisibility in its early stages.
Immature larvae require very little food, which means their presence produces undetectable damage. In the later stages of life, however, this rapidly changes.
Larvae eat 50 times as much, and at this stage, entire crops can disappear overnight.
Should New Zealand’s agricultural industries be worried? It depends. If the speed of our response is appropriate and our actions are ongoing and consistent, we have every chance of avoiding the Sub-Saharan fate.
Initially, insecticide programmes were the strategy of choice for many infected countries, but results have been disappointing for several reasons.
One reason is the FAW’s behaviour. Almost immediately after larval hatching, neonates move into the whorl region of corn plants where they are protected from foliar insecticide sprays. Aside from this physical defence, some species of armyworm have developed resistance to traditional chemistry which makes them difficult to eliminate.
In response, scientists in Switzerland are developing baculoviruses to combat the fall armyworm. Baculoviruses are a family of viruses that are species-specific, meaning they only infect certain insects.
This narrow targeting is crucial because it poses minimal risk to non-target organisms, including humans and beneficial insects. The environment is also immune.
Trials are still ongoing, but several baculoviruses have shown promise in infecting and eliminating fall armyworm larvae. These baculoviruses also amplify transmission by releasing large amounts of the virus into the environment to infect other armyworms.
If these bioinsecticides become certified and registered for use in New Zealand, they could prove decisive in protecting our country. Key Industries is one company seeking to bring an approved baculovirus into New Zealand.
Act this spring. Before an effective biopesticide becomes available, there are proactive measures that farmers and growers can take. The first step is comprehensive monitoring. This may sound passive, but it is not.
Monitoring allows for early detection of caterpillars before they get into the plants, which is an absolute key to beating this horde.
Several monitoring-trap options are available. One is the pheromone monitoring lure, a trap specifically designed to capture the fall armyworm.
These imported traps serve two purposes. First, they attract, capture and kill adult moths. They also allow farmers and growers to gauge the level of armyworm influx.
The time to lay pheromone monitoring lures is in late spring, when crops are susceptible to damage. The recommended placement pattern is on the edges of fields, or 16 to 24 rows from the edge of a field. Windward side is recommended so that pheromone will be blown into the field.
Trap maintenance is also a key. Check the lure twice a week and change them out each month.
As with all potential threats, people must make up their own minds as to the validity of the danger. For those who consider the risk of fall armyworm to be low, this article may amount to scaremongering. For those who perceive the threat to be real and significant, to be forewarned is to be forearmed.
Rural contractor article supplied by Key Industries.