Digging in and looking for fall armyworm (FAW) pupae could be one of the best ways to assess a paddock’s risk this coming winter and spring.

FAW expert Dr Melina Miles, principal entomologist at the Queensland Department of Agriculture and Fisheries (DAF), recently spoke at GRDC Updates, both online and in person, about continuing risks this year.

It follows what has been one of the most destructive and distressing seasons for maize and sorghum growers since FAW was found in Australia in 2020.

Dr Miles works on GRDC and DAF projects aimed at developing FAW economic thresholds and management guidelines for sorghum and maize.

At the GRDC Goondiwindi Update, she spoke about paddock assessments. “There is really no other way to assess the risk than to get down on your hands and knees with a trowel and have a look at whether you are retaining pupae.

“There are probably many young growers and agronomists out there who have never had the pleasure of pupae sampling, but I think that this is the best option available. Certainly, it is until we have a better understanding of FAW population dynamics.”

Pupae sampling can be done immediately before or after a crop is harvested.

“Sampling early tells you if you have pupae in the ground at the end of the season. It is likely that a proportion of that population will become moths and emerge between now and spring.

“Sampling in August to September will give you an idea of the carryover population, and how that increases the risk to early sown maize and sorghum.”

Pupae sampling also helps determine the regional risk of locally generated FAW populations.

“White French millet and forage sorghum crops are also worth investigating. We do not know what proportion of the FAW population in any region is locally generated, or results from immigration.”

The research team is not recommending action based on the results; rather, the sampling helps better understand population dynamics and on-farm risk.

Crop stage no longer a barrier

Dr Miles has been at the research helm since FAW was identified in Australia. She says this year has been unlike the previous three. “This season we have seen FAW persistently laying on plants through the reproductive stages, causing grain damage.”

Up to now, the focus has been on losses caused by vegetative stage damage. Research into crop damage at the reproductive stage was not considered a priority until this year.

“We have spent the last few years – 2021, 2022 and 2023 – trying to get FAW to infest crops post-flowering so we could have a look at grain damage.

“And we have been spectacularly unsuccessful at that. Based on what we’ve seen this year, I now think the opportunity for larvae to go between heads and late tillers to sustain themselves was missing from the sorghum trials.

“So, I think we’ve learned something quite significant there,” she said.

In many regions, FAW has previously been present, but not at damaging levels. “It came as quite a surprise to people to find that so quickly after emergence, particularly on the January and February plantings, that crops were just disappearing, almost before our eyes.”

Sustained infestations of two large larvae per plant have been enough to severely restrict plant growth.

With just four seasons to reflect on, and no direct investment in research into the potential population drivers, Dr Miles says the team can only speculate on why this year has seen such high FAW activity, using experiences with other Lepidoptera pests, such as Helicoverpa, to draw conclusions.

“Typically, mild winters and abundant hosts through winter and spring provide opportunities for caterpillar pest populations to build up early and continue to build through spring and summer,” she says.

“It is also possible that meteorological systems associated with the Queensland cyclones in December and January facilitated the movement of FAW moths from north to south (or west to east).”

For information about identification and registered chemical control options, growers should contact their local advisers and visit the APVMA PubCris website or the GRDC Fall armyworm portal.

More information can also be found on The Beatsheet.