GROWERS harvesting swathed crops in Western Australia’s south coastal regions are advised to be aware of potential grain contamination by ‘vagrant’ insects, including ladybirds which are believed to be in high numbers this year.
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Vagrant insects are insects incidentally harvested with grain, but do not damage it.
Grains Research and Development Corporation (GRDC) funded research previously conducted in the region investigated insects which can contaminate grain from swathed and standing crops, and provided management advice.
Department of Agriculture and Food (DAFWA) entomologist Svetlana Micic, who helped conduct the research, said growers could reduce insect contamination by swathing crops at the correct swathing height; harvesting swaths as soon as they were ready; and harvesting during the day.
Some common vagrant insects include bronzed field beetles, European earwigs, Rutherglen bugs and sometimes ladybirds.
Ms Micic said these insects, except ladybirds, sheltered on the ground under the swath.
“The longer the swath remains on the ground, the more insects accumulate under it,” she said.
Ms Micic said the department’s research found that bronzed field beetles, rutherglen bugs and European earwigs were more likely to be harvested with grain if the swathing height was too low or the swath had fallen on to the ground.
“If the swath is on or close to the ground, harvesters fitted with crop lifters, which are better able to pick up low swaths, will pick up more insects sheltering on the ground, than harvesters fitted with belt pick-up fronts,” she said.
“But crop lifters are also able to collect more grain.”
Ms Micic said ladybirds were commonly found sheltering in the swath rather than on the ground under it.
“This has been observed mainly in canola swaths from crops that had aphids,” she said.
“By the time the canola has been swathed the aphids are no longer present.
“This year there have been many crops with high aphid numbers in the South Coast region.
“It is these crops that may have high ladybird numbers and some paddocks may require seed cleaning to get the grain to acceptable levels.”
Ms Micic said a lot fewer insect contaminants were found in grain harvested from standing crops.
“While farming areas experiencing dry conditions are doing more direct heading of crops such as canola, the South Coast has had wetter conditions, causing more canola crops to be swathed,” she said.
Ms Micic said that, with the exception of ladybirds, the GRDC funded research found more insect contaminants in grain harvested at night than in grain harvested during the day.
“This is because at night insects move from under the swath, in to it, whereas during the day most of the insects are under the swath.
“Growers harvesting swaths at night need to be aware that there are likely to be more insects in the swaths, and may wish to mix this grain with grain harvested during the day,” she said.
