Insect contamination in grain from swathed crops is more common than in direct harvested grain, according to GRDC-supported DAFWA entomologist Svetlana Micic.
"Careful management such as harvesting swaths as soon as the grain is ready and avoiding night harvesting when insects move from under swaths and into them, will reduce contamination," Ms Micic said.
No insecticides are registered for under swaths, hence should not be used.
Ms Micic advised swathing crops at the right height.
If swaths are near the ground, more insects are likely to be harvested with the grain.
"For cereal crops that's 125 millimetres. Swath canola above the first fork, but only if yield is likely to exceed one tonne per hectare. The swath is then supported by stubble," she said.