Western Australian grain growers are advised to keep a close eye on emerging crops following recent reports of significant caterpillar activity on volunteer crop regrowth, clover and weeds in all port zones - 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 GRDC investment - says potentially damaging species have recently been found in unusually large numbers.

These species include:

• native budworm (Helicoverpa punctigera);
• webworm (Hyphantria cunea);
• weed web moth (Achyra affinitalis); and
• pasture day moth (Apina callisto).

Regional activity

Dr Severtson says 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.

He says the influx of caterpillars is the result of considerable summer rainfall from cyclonic activity in the grainbelt and in WA's north-eastern pastoral areas.

"This resulted in unusual moth flights to the State's northern and central agricultural regions," he says.

"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."

Monitor and report

Dr Severtson says caterpillar species can be difficult to identify and he recommends 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 says.

Dr Severtson says diamondback moth (DBM) larvae have 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 says DBM are 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," Dr Severtson says.

He says the DBM larvae had been identified as part of a GRDC-invested project aimed at providing WA canola growers with earlier warnings 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 (SARDI), 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," Dr Severtson says.

Be alert to new invasive species

Correct identification of fall armyworm is a critical part of its management. The larvae of this pest change significantly in appearance as they grow (this picture is indicative only). Photo: University of Florida

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

This 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 says.

"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."

Other caterpillars to watch out for

DPIRD's website has information about management of and economic thresholds for budworm and pesticide options. GRDC also has a video about budworm control.

GRDC has latest information to help growers manage DBM and how to manage resistance. SARDI also has a DBM PestFacts article.

To stay updated with the latest pest and disease information, sign up for the DPIRD PestFax newsletter and PestFax Map, or email PestFax@dpird.wa.gov.au.

GRDC Research Code: DAW1905-010RTX

More Information: Dr Dustin Severtson, DPIRD, 0422 157 769, dustin.severtson@dpird.wa.gov.au