Caterpillars pose threat to WA cropping regions

Grain Central, April 23, 2020

SIGNIFICANT caterpillar activity has been reported on volunteer crop regrowth, clover and weeds in all cropping regions of Western Australia, but especially in the northern and central grainbelt.

WA Department of Primary Industries and Regional Development (DPIRD) entomologist Dustin Severtson, who works on projects with Grains Research and Development Corporation (GRDC) investment, said potentially damaging species had recently been found in unusually large numbers.

Dustin Severtson

These species included native budworm (Helicoverpa punctigera), webworm (Hyphantria cunea), weed web moth (Achyra affinitalis) and pasture day moth (Apina callisto).

“Caterpillars and other pests such as aphids may transfer from the ‘green bridge’ into vulnerable emerging crops if the green bridge is not destroyed at least two weeks before crop emergence,” Dr Severtson said.

He said the influx of caterpillars was the result of considerable summer rainfall from cyclonic activity in the grainbelt and in Western Australia’s north-eastern pastoral areas.

“This resulted in unusual moth flights to the state’s northern and central agricultural regions,” Dr Severtson said.

“Native budworm caterpillars have been found at Mingenew, Ballidu, Narrogin and Calingiri, and there have been reports of webworm moths and pasture day moths across the central agricultural region.”

Dr Severtson said caterpillar species could be difficult to identify and recommended growers use the free PestFax reporter app ( to request a diagnosis.

“To use the app, growers simply need to take clear, close-up photos of the caterpillar and plant damage, and attach these along with any helpful background information,” he said.

Diamondback moth

Dr Severtson said diamondback moth (DBM) larvae had also been identified in the ‘green bridge’ in Brassica species such as wild radish and volunteer canola plants, with hotspots at Geraldton and Esperance.

He said DBM were generally of greatest risk to crops in early spring when temperatures began to rise, but in previous years the species had caused damage to the leaves of young plants.

“It is rarely worthwhile spraying for DBM at this time of the year, but growers should be vigilant and monitor crops if we have warm days during early crop growth stages,” he said.

Dr Severtson said the DBM larvae had been identified as part of a GRDC-invested project aimed at providing WA canola growers with earlier warning about potential DBM outbreaks, so they could pro-actively manage the pest.

“The project, conducted by DPIRD and the South Australian Research and Development Institute, involves surveillance to determine the Brassica hosts for DBM that may be present in summer and autumn, and assessing whether these hosts provide a ‘reservoir bridge’ for the pest between growing seasons,” he said.

Fall armyworm

Dr Severtson also encouraged growers who suspected that the invasive pest fall armyworm (Spodoptera frugiperda) might be present in their paddocks to submit a report using the PestFax app.

The highly mobile insect was first detected in Australia in a maize crop in northern Queensland in February and has since spread to the Northern Territory, and recently to Kununurra and Broome in WA.

“Although this pest seems to favour maize and sorghum, the list of host plants for fall armyworm includes cereals, canola and pulses, so growers should be vigilant,” Dr Severtson said.

“Fall armyworm larvae change significantly in appearance as they grow, but the mature fall armyworm caterpillar has a distinctive inverted ‘Y’ marking on its head area and four large spots – in a square arrangement – on the dorsal surface of its second last segment.”

Source: DPIRD

More information about fall armyworm, including how to identify it, is available on the GRDC website and on the DPIRD website by searching ‘fall armyworm’. A GRDC podcast about fall armyworm is available at

Information about management of and economic thresholds for budworm can be found on the DPIRD website and pesticide options for budworm control are also available on the DPIRD website. A GRDC video about budworm is available at

Current information to help growers manage DBM can be found in the GRDC Diamondback Moth Fact Sheet or on the DPIRD website. Information is also available in the GRDC Resistance management strategy for diamondback moth in Australian canola and the SARDI PestFacts article Keep An Eye On Diamondback Moth. A GRDC video about DBM is available at

To stay updated with the latest pest and disease information, sign up for the DPIRD PestFax newsletter and PestFax Map by visiting the DPIRD website or emailing [email protected].





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