Grain growers considering treating crops for native budworm have been reminded to be aware of chemical withholding periods and to weigh up whether it is worth the cost.
Native budworms are still being found in pulse and canola crops, with recent surveys detecting the pest from Boyanup to Kojonup and Esperance.
Department of Agriculture and Food entomologist Svetlana Micic said with harvest imminent it was important to ensure there was no risk of chemical residues to crops.
“Harvest is just weeks away for many growers so they should be aware of insecticide withholding periods,” she said.
“Many traditional pyrethroids have a 21 day withholding period in canola but there are newer generation chemicals that have a shorter period of seven days or less.
“Growers should also remember that windrowing (swathing) is classified as harvest and take that into account when determining their withholding period.”
Ms Micic warned that swathed canola crops could still be at risk of damage from native budworm.
“This will occur if the crop is swathed when many pods are still green with soft seed or if swath drying is prolonged due to cool damp conditions,” she said.
Ms Micic advised growers to assess whether it was worth treating for native budworm before spending money on spraying.
The department has undertaken extensive research to assist growers to calculate the economic threshold for treating for native budworm.
“The calculation can be tailored to growers’ individual situations, taking into account grain prices and control costs,” Ms Micic said.
“The economic threshold is determined by the control cost per hectare divided by the combined value of the kilograms of crop eaten by every caterpillar netted in ten sweeps and the price of grain per hectare.”
Growers can get more information about the native budworm and the threshold calculator via the department’s website at agric.wa.gov.au and searching for ‘native budworm’.
To stay updated with the latest pest and disease information sign up for the department’s PestFax newsletter and PestFax Map service by searching for ‘pestfax’ on its website.
Details of insecticide withholding periods is available from the Australian Pesticides and Veterinary Medicines Authority by searching for ‘pubcris’.