GROWERS in the Esperance region fear a large infestation of mice this season.
Mice are nearly always present in paddocks but largely go unnoticed when numbers are low - but they breed quickly under favourable conditions.
While the Agriculture Department says it has not been receiving reports of increased mice numbers, east Esperance grower Simon Schlink estimated he had about 800 mice per hectare in some of his paddocks.
"We have done baiting and it has worked okay but in a few months numbers have built up again," he said.
Mr Schlink, who farms in the Mt Howick area, said the mice would be waiting to feed on emerging crops after breaking rains.
"They can take out huge areas and if bad enough they will take out an entire crop," he said.
He said canola and lupins were less likely to bounce back if damaged; last year mice ate lupins as they came out of the ground and also dug up seed before the crop emerged.
Mr Schlink said if he didn't spend money on bait, he would lose more money in crop damage.
He said it was recommended that bait be laid when mice populations reached 250 mice/ha.
However, mice numbers as low as 200 mice/ha could cause significant economic damage, while 1000 mice/ha densities have the potential to destroy 5pc of a freshly sown crop per night.
There were several methods of assessing mice numbers, either through using bait cards soaked in canola oil or by counting the number of active mouse holes.
Active holes can be assessed by lightly covering them with soil and counting the number of active holes the next morning.
If for example a strip of paddock 100m X 2m wide is assessed and found to have five active holes, the estimated population would be 500 mice/ha.
Growers can report results to their local department biosecurity officer to determine if control methods are warranted.
Esperance Rural Services agronomist Les Spencer said hopes that summer rain would drown the mice faded when the rain did not arrive.
He expected baiting would begin in the next few weeks to prevent damage to this season's crops.
Mr Spencer said Mr Schlink had ordered four tonnes of Mouseoff zinc phosphide bait to cover 1000ha.
He said it was no secret mice could multiply quickly and that two mice could exponentially produce 28,000 mice over six months.
He said that last year mice were taking second nodes off near-mature crops in the region and some aerial bating was required.
Agriculture Department biosecurity officer Errol Kruger, based in Moora, said that when mice build up to large numbers, mice could be a serious pest problem to grain producers and cause damage of $100m a year nationally.
He said prevention was always the best option by minimising spilt and waste grain, cleaning up rubbish dumps and hay and grain stores, and burning all edible waste.
The Department has said baiting is a measure of last resort, which some people have blamed for the build-up of numbers.
"I think the major issue is monitoring to see what sort of numbers are around," Mr Kruger said.
He said control work was carried out against mice in August and September east of Esperance, and since then he had not heard anything more about mice problems in the area.
Landmark Esperance agronomist Troy Bungey said he had only received some isolated reports from growers with mice problems, but expected the number could increase if the area received rain in the next few weeks.
Mr Bungey said clients from Munglinup, west of Esperance, reported mice damage to canola and wheat last year. Farmers who did not bait last year would have the highest mice numbers this year.
He said because there had not been any summer rain, farmers in the area would probably need a good inch of rainfall before they seeded their canola, which usually begins in mid-April.
"It is one of the driest seasons we have had," he said.
Meanwhile Elders Esperance has not heard of increased mice numbers in the area, but Elders Albany agronomist Mark Lawrance said there had been an isolated report at Gairdner.
He said mice had caused some slight damage to canola on the same farm last year, which was not baited, and he would soon be making estimates on the mice to decide if baiting was required before seeding.
"It looks like the numbers have carried over the summer," he said.