Fall Armyworm in Australia

The fall armyworm is a recent invasive pest in Australia. Here is the essential information – identification, basic information and control options…

The fall armyworm, Spodoptera frugiperda, continues to spread across Australia. Since first being detected in mainland Australia, in far North Queensland in early 2020, it has now spread across most of the eastern seaboard and across into Western Australia. Its rapid spread in Australia has mirrored its spread across the rest of the world – native to the Americas, since 2016 it has spread across 65 countries in Africa and Asia. None of these countries has attempted eradication, largely due to the futility of the exercise; adult moths are capable of flying 100-200 km making containment impossible. So, although the armyworm remains a reportable pest in Australia, it is here to stay. What does it look like, what damage does it cause and how can it be controlled? (Or rather managed?)

 

Fall armyworm identification

The fall armyworm is quite similar to the native armyworm and some other caterpillar pests, such as the cluster caterpillar. Although the caterpillar can vary in colour from light green to brown, it has a distinctive dark head capsule with an upside down ‘Y’ between the eyes. It has four dark spots arranged in a square, with single pairs of paler spots on the other body segments. On older larvae, three pale stripes run the length of the body. They lay their eggs (0.5 mm) in masses on leaves covered in a furry mass, much like the cluster caterpillar. The nocturnal adult moths are mottled grey/brown in colour, with a body length of 15-20 mm and a wingspan of up to 40mm.

 

Fall armyworm caterpillar
The fall armyworm caterpillar has a characteristic dark head with an inverted ‘Y’ pattern, along with four dots arranged in a square on its last body segment

 

Fall armyworm moth
The adult Spodoptera frugiperda is a very plain brown moth

 

Fall Armyworm Life cycle

Being a tropical pest, the warm temperatures deliver a rapid life cycle. Females can lay up to 1000 eggs, which hatch in 3-5 days. The caterpillars progress through six instars over 2-3 weeks before pupation. The adults are short lived, living for around 10 days.

 

Distribution

The fall armyworm is a pest of tropical and sub-tropical areas, thriving in warm, moist areas. In Australia this means it will become a year-round pest in much of the coastal regions in the top half of the country, from northern New South Wales around into Western Australia. However, with the ability of the moths to fly long distances, it will also become a pest in the warmer months around much of coastal Australia and inland into cropping areas, which is why this is a pest of significant concern.

 

Pest status

The fall armyworm will attack a wide range of plants – they are known to feed on more than 350 plant species, including a wide range of cereal, fruit crops and grasses. In residential areas, they can be a problem in lawns. The young larvae attack the leaves, causing a ‘windowing’ effect. The older larvae will often hide and feed down in the leaf whorls. Older larvae will also feed on roots and developing seed heads/fruits.

 

Fall Armyworm Control Options

As significant damage can occur in a few days, treatment at the first sign of damage is essential. Use an insecticide spray labelled for caterpillar pests and for the use situation at hand, be it a lawn situation or on food plants. Where the fall armyworm is attacking cereal crops, check down in the leaf whorls for the presence of larvae, as it can be difficult to get insecticide into these protected areas. In such situations it is important to choose a product that has systemic effects (movement within plant) and/or translaminar effects (movement into leaves), to target the hard to reach pests.

There is a high level of resistance to pyrethroids, so it is generally recommended to use a different class of insecticide. State governments recommend using selective insecticides such as spinosyns, emamectin benzoate and chlorantraniliprole. Although chemicals such as chlorantraniliprole also provide some residual protection, in areas where fall armyworm is present, there is always the potential for reinvasion.

More information on caterpillars in lawns and general lawn care information.

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