FAW attacking early sown winter cereals: QDAF

Liz Wells, May 1, 2024

FALL ARMYWORM is attacking some early sown winter cereals after building up populations to unprecedented levels in summer crops and other feed sources.

Speaking in an online session today with 150 attendees, Queensland Department of Agriculture and Fisheries principal entomologist Melina Miles said this move into winter cereals was the latest development in FAW’s most damaging season yet.

The pest arrived in Australia four years ago, and has previously confined its attacks to row crops, namely corn and sorghum.

However, a hot, humid and wet summer has seen FAW numbers boom and populations spread.

“I find it hard to think of anywhere, except for maybe Tasmania, where you won’t see fall armyworm if you put in a susceptible crop,” Dr Miles said.

“Right now, having had summer crops or forages on your properties…increases the likelihood of seeing fall armyworm in winter cereals, but if you haven’t…the moths are highly mobile.”

Dr Miles said excessive FAW pressure on winter cereals in autumn should not be expected annually.

“I’m firmly of the opinion that what we’re seeing this year is an outbreak…and in subsequent years, you go back to conditions where (fall armyworm) go back to preferred crops.”

Some resowing already

FAW’s impact on summer crops has already been well documented this season.

Following infestations in grain and fodder corn, grain and forage sorghum, and White French millet, FAW damage is being documented in early sown oats, wheat and barley, as well as sugarcane and Rhodes grass at establishment.

“To our surprise, we find ourselves in the situation where winter cereals that were planted early have been quite heavily impacted.

“It’s not an experience we’ve had previously.

“We’ve had reports from Central Qld to the Mid North Coast of New South Wales.”

Dr Miles said growers and agronomists have assisted the knowledge-gathering process, and some oat crops particularly have had to be resown following patches being eaten out by FAW.

Her message to growers in areas where FAW has been around this season, and even where they haven’t, was clear: “It is absolutely critical that you’re checking all winter cereals within 5-7 days of emergence”.

“One of the things that’s really surprised me is how vulnerable winter cereals are to stem damage.”

Dr Miles said Rhodes grass as far into the tropics as North Queensland was vulnerable too, but oats appeared to be the crop of choice, and has provided the opportunity for FAW to develop to a damaging stage and move into “whatever else is green”.

“I would say that if you’re in any area where there’s been fall armyworm over summer, and you’re planting winter cereals, this applies to you.”

Dr Miles said the big summer crop, and the early start to winter-cereal  sowing, has probably contributed to the build-up in FAW pressure.

“Putting winter cereals in in mid-February when fall armyworm was peaking has really put those crops in the firing line.”

Larvae does not equal disaster

Dr Miles said agronomy was playing a big part in ensuring crops got off to a flying start, and this was the best protection against FAW.

“Seed quality and uniformity, and the ability to establish rapidly, and recover quickly, can be compromised if agronomy is not right; that seems to be a pretty common theme.”

She has asked growers to consider FAW as a reason for patchiness in crops.

“I want to hammer home that fall armyworm could be a factor for poor establishment.”

Growers and agronomists have advised that rows of dead seedlings have been seen in oat crops.

“They are dying at a much higher rate than we had seen in summer crops.”

If small holes in leaves are visible, Dr Miles suggests checking crops after dark, as larvae can sometimes be hidden during the day.

Dr Miles also said the size of the larvae and the health of the crop needed to be weighed up in light of each other, with a small crop with big larvae more likely to require action than a crop with big biomass and small larvae.

The need to resow has brought with it the need for careful checking of neighbouring growth, as evidenced by a recently inspected Downs crop.

“By the time you have patches you want to resow, you also have large larvae.

“These larvae were stopping in headlands and feeding on grasses, so keep an eye on neighbouring crops.

“Those larvae do have the capacity to walk quite a large distance to find things to eat.”

Help from nature

Dr Miles said natural mortality among FAW was high, and that 90 percent of first instar larvae do not make it to the sixth and final stage.

“The likelihood of them dying from wind, rain, predator et cetera is very high.”

Delaying of planting winter cereals could also be an effective way to minimise exposure to FAW damage.

Dr Miles said natural predators including spiders, ladybeetles, and pirate bugs can make a difference to FAW populations.

Warlock, with its active ingredient benzoate, can be considered for use in wheat, with permits available on the APVMA website, but an effective option is yet to be registered for oats, barley, or pasture.

Based primarily on research done in the US, FAW cannot be expected to fade with the first frosts of the season.

“With a reasonable frost at minus 5, we’re still getting good levels of survival of all stages.”

Dr Miles said the longer FAW larvae live, the more likely they are to not make it to the most damaging size of 12mm.

FAW arrived in Australia with some resistance to insecticide, and Dr Miles said this did not appear to have increased.

Dr Miles said synthetic pyrethroids were likely to be the least effective applied treatment for larvae.

“At best, you might see 10pc control.”

Indications are better results on small larvae of 60-70pc control can be expected from carbamates.

“I think that biological control options are highly desirable for grazing…but these are things for industry to consider as we go forward.

In the absence of specific FAW advice, Dr Miles said helicoverpa threshold calculations as found on The Beatsheet can be used for summer crops.


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