Fall armyworm monitoring

Local Land Services staff manage the surveillance of Fall Armyworm (Spodoptera frugiperda). This pest is a serious threat to industries such as grain, rice, cotton, vegetables, and sugarcane. Early detection is vital to minimise its spread and impact.

Pest control is crucial due to inconsistent seasons since Fall Armyworm established in NSW. Consultants and growers can use this information to make informed decisions.

We have surveillance traps in the following regions:

• North West
• North Coast
• Northern Tablelands
• Central West.

Identify and recognise

There are a number of species which are identified as armyworms, the most widely spread being the Common armyworm. This is the caterpillar of the native noctuid-moth (Leucania convecta, known previously as Mythimna convecta).

Distinguishing between the various armyworm species can be difficult but due to similar habits, damage and methods of control, identification of individual species is not always essential. Key characteristics for armyworms include:

Adults:

• Wingspan up to 40 mm.
• Wings fold in inverted ‘V’ over abdomen.

Larvae:

• Up to 40 mm in length.
• Smooth bodies with minimal fine hairs.
• Body colour can vary but three longitudinal white stripes extend from the ‘collar’ (behind the head).

Eggs:

• 0.5 mm in diameter.
• Light brown, turning darker as they develop further.
• Often laid in masses.

It should be noted that armyworms can sometimes be confused for Helicoverpa caterpillars and Cutworms (Agrotis spp.).

Damage

Armyworms feed on leaf tissue. They typically leave a scalloped/tattered appearance on leaf margins and in drastic cases, entire leaves may be severed from the stem. 

During crop vegetative stages, large populations can cause severe loss of leaves, with heavy feeding leaving only the main stem of the plant.

As the season progresses into spring, further yield potential can be lost as armyworms move onto the flag leaf.

Head-lopping, particularly of wheat and barley can be quite devastating to final yield. Head-lopping is caused when crops begin to senesce and leaves dry up.  Larvae will move up the plant to feed on the last green remnants which are the nodes that attach the heads to the main stem. Because of this, the connection will be cut, lopping the head.

Prevalence and severity

Fall Armyworm is an insect pest first detected in NSW in 2020. 

It has since spread to all key summer cropping regions of NSW which includes: 

• North Coast
• Northern Tablelands
• North West
• Hunter
• South East
• Central West
• Riverina
• Murray. 

Populations are also established in northern Western Australia, Northern Territory, and Queensland from early 2020.

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Manage, monitor and control

Late in the day is the best time to monitor for armyworm.

Ideally, monitor crops at least fortnightly during vegetative stages and then increase to weekly if larvae are found as the crops begin to senesce. Look for signs of caterpillar droppings (frass) on the ground, damage to leaves and plant heads.

Early identification of the population is vital to making an informed decision around whether control is required.

Beat sheets have been found to be the most effective in indicating the population of small and medium sized larvae as it does a better job dislodging them from the canopy.

Large larvae can often be found near the base of plants. It is highly recommended to further examine soil near the crop row and underneath litter.

Armyworms tend to be more active at night, so identifying the proportion of large larvae, which are responsible for the majority of larval damage, close to the ground during the day can improve accuracy of population surveys.

Consider the proportion of the population which are capable of causing damage (instar 4-6) and those that are smalls. 

Small larvae take 8-10 days to reach a size which is capable of head-lopping, so a large population of smalls in a near harvestable crop may mean control may not be required.