Slugs march north and west into medium rainfall zones

Agronomists and growers across southern NSW, Victoria and eastern South Australia are noting high burdens of both grey field and black keeled slugs, the two major pest species in Australian grain systems.

The slugs are particularly damaging in broadleaf crops such as canola and pastures, but can also cause damage in cereal crops in high numbers, mainly in high rainfall zones.

Cesar entomologist and pest management specialist Paul Umina said traditionally severe slug damage was limited to high rainfall zones, but in recent years there has been a steady march north into drier regions.

"We're increasingly seeing slugs at economically damaging levels into the Wimmera and into those more medium rainfall zones rather than just areas like the Western District or south-east South Australia," Associate Professor Umina said.

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"The season has been a perfect storm, it was a mild summer and then it has been wet through the early autumn which has allowed them to breed up."

In the Wimmera in Victoria, slugs are becoming a problem in areas where farmers have not had to worry about the pests previously.

Jade Clark, Nutrien Ag Solutions Dimboola branch manager, said black keeled slugs were being noted at damaging numbers around Wail, between Dimboola and Horsham.

"We're seeing them move further north following the wet season," Mr Clark said.

"There was over 700mm in the area last year, far above the long term average and that residual moisture, combined with a good April break, has allowed them to make their way up here."

"We're really seeing them come out of the scrub and damaging the edges of paddocks, it is something we don't see often, snails are normally the main pest species here."

Mr Clark said clients in a wetter part of the Wimmera towards Goroke were facing an even heavier infestation.

"For most of our customers over there they are automatically baiting behind the seeder in canola, we're just trying to keep on top of them as they can get away quickly and cause so much damage."

James Heffernan, Nutrien Ag Solutions Naracoorte, said it was a similar story just across the border.

"We've seen them build in numbers in recent years and this year it's definitely allowed them to breed up and become a major problem," he said.

"We're seeing them everywhere whatever the farming system, the wet last year, the mild summer and the good autumn break have really seen numbers increase."

"The switch in farming systems to a focus on standing stubbles is also providing habitat for them and with the early break people did not get through the burning program they were hoping to which would have helped keep numbers down."

Mr Heffernan said farmers were closely monitoring a spread of the pests across paddocks.

"We normally see them confined to known problem areas within the paddock, now we're seeing them everywhere."

He said most farmers had put out one bait and added there could be a second for many particularly in vulnerable crops.

"It's been a real influence on planning for the season - people don't want to get it wrong as it can be so damaging."

One promising factor was that early observations suggested baiting had been effective.

Andrew Russell, GRDC southern panel chair and farmer in north-eastern Victoria said the region was also in the grips of one of the worst slug outbreaks on record.

"We're seeing them on both sides of the (Murray) river pushing up into traditionally drier areas," he said.

"It's been really wet for well over a year so they are getting some very favourable conditions."

He said the slug pressure, combined with heavy stubble load, meant people had looked to burn stubbles, many for the first time in years.

However, the early break meant not all stubbles were burnt, meaning more monitoring and potential need for baiting.

Mr Russell said farmers were closely monitoring numbers but were not automatically baiting.

"A lot of work is going into monitoring whether numbers are at economically damaging levels in individual paddocks."

"There's very heavy pressure and we're keeping an eye out on it as best as we can, the good news is that there is no squeeze on supply of bait so we can get out there and control them if need be."

Horsham farmer Tim Rethus said the heavy slug burden had been frustrating.

"We'd love to see some sort of precision agriculture solution, at present we're just putting out a set amount of bait across the paddock, we identified zones through yield maps where we thought we might be able to variable rate the bait out but because the slugs are moving it is not necessarily proving effective," he said.

"Burning may lower the amount of habitat but it doesn't kill the slugs so that's not something we're keen on doing."

Ass Prof Umina had a small sliver of good news for growers in medium rainfall zones experiencing issues.

"The high numbers are very much because of the wet and mild seasons we've been seeing."

"The switch to no-till may provide better habitat for slugs but they are very responsive to the season so you won't see this pressure in those areas if it is drier."