Fall army worm is back: season two

Fall Army Worm arrives at Croppa Creek ahead of second summer invasion

Feed Management
Corn leaves mown down by what looks like machine gun fire. A heavy approach with knockdown chemical at first sighting of fall armyworm can have disastrous effects.

Corn leaves mown down by what looks like machine gun fire. A heavy approach with knockdown chemical at first sighting of fall armyworm can have disastrous effects.

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After over-wintering in Queensland's sweet corn growing districts the recent pest Fall Army Worm is set to wreak havoc on NSW cropping with the first confirmed sighting west of the range at Croppa Creek this week.

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Season two of the fall army worm invasion has descended on NSW maize growers with the confirmation at Croppa Creek, NSW, of moths found in pheromone traps installed by Local Land Services officers.

This is the season's first sighting west of the dividing range and marks an early start to the pest's incursion after over-wintering in the sweet corn districts of Queensland's Lockyer Valley.

The moths were first detected in Australia's far north in February 2020 and were trapped north of Moree, NSW, in late September.

The pest previously travelled the world and built up tremendous resistance to conventional chemistry.

NSW coastal producers learned a lot from last year. By the end of harvest, Spodoptera frugiperda had affected corn as far south as Shoalhaven.

This season, for the first time in Australia, growers have an alternative control in the form of a naturally occurring virus, manufactured into a convenient spray by the Toowoomba company, AgBiTech, and imported under APVMA permit from their US facility.

It has already made a difference to corn grown in North Queensland and the Ord Valley, WA, but has greatest efficacy when caterpillars are small and so growers must monitor their paddocks for emerging grubs and target these - at first and second instar - for best effect.

Phil Armytage from AgBiTech says a single female moth lays 1000 eggs, of which only 16 per cent survive.

Half of those will be female and in just four generations numbers can swell to 41 million larvae burrowing into the twisted growing centre of corn plants where they and are well shielded from conventional chemicals.

Fawligen works just like Vivus Max, another baculovirus-based biological control made by the home-grown company that began life in an old farm shed in Dalby, Qld.

Their US facility grows out a million larvae a day specifically to make the baculovirus to specifically target emerging grubs without harming vital natural predators like highly sensitive parasitic wasps.

It can be sprayed from a boom unit attached to a tractor, or from the air or even through irrigation lines in a process known as "chemigation" with each millilitre of product containing 7.5 billion occlusion bodies; each one harbouring infectious particles of the host-specific virus.

However this organic spray - a combination of pulverised dead infected caterpillar larvae and water - must be used in conjunction with other management practices to keep the corn loving larvae under control.

Last year's learnings were basic in their premise: plant corn early when pest pressure is at its lowest and avoid broad-spectrum insecticides.

Paddocks that weren't managed well last year were overrun by grubs, eating their way out of the centre whorl where sprays never penetrated and into an environment where natural predators had been culled.

Boambee, NSW, dairy farmer and corn-silage grower Jason Bake will repeat his efforts of last season, which involved extensive moth trapping and grid-pattern monitoring of the crop for early signs of grub followed by a soft spray to keep beneficial insect populations high.

Last year he used Vivus Max to lower the number of common Helicoverpa grubs so that predatory insects could concentrate on FAW.

He observed that a high number of little grubs were quickly culled by the cannibalistic tendencies of larvae to eat each other.

Richmond Valley corn grower Paul Fleming said last year he experimented with an early spray of DuPont Steward followed by FMC's Altacor, but will try the latter chemistry first this year.

"I wouldn't like to say that I know what to do," he admitted.

"But Altacor works with a trans-laminar effect, moving through the leaf, whereas with Steward the grubs have got to eat where the chemical lands and if they are in the centre of the growing stalk you won't get it to them.

"My tactic this year will be to not grow as much corn, plant it early in the season, and to spray early with Altacor."

Meanwhile, Mr Armytage of AgBiTech predicted wide-spread resistance to Altacor in four years' time.

"Biological controls are not as effective as conventional chemistry so for that reason those tools should only be used later in the season," he said.

"Plant early, control with ultra-soft prevention measures to get a lid on the population and save the hard hitting chemistry closer to tassling."

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